Method for detecting influence of phosphorus chemical industry solid waste modified land reclamation soil on crops

Abstract

The invention discloses a method for detecting the influence of phosphorus chemical industry solid waste modified land reclamation soil on crops, and relates to the technical field of soil improvement, and the method comprises the following steps: 1, selecting test raw materials: the raw materials mainly comprise ardealite, phosphate tailings and plough layer soil of a local unutilized land, and firstly, leaching for 2-3 times by using water washing equipment in a factory so as to reduce the concentration of harmful elements. According to the method for detecting the influence of the phosphorus chemical industry solid waste modified land reclamation soil on the crops, the content of five heavy metals in the crops is combined, the heavy metals in corn planted in the land reclamation soil using phosphogypsum and phosphorus tailings reach the standard, and the method can be applied to agricultural production; paddy rice planted in the ardealite land-making paddy field and potatoes and buckwheat planted in the dry land firstly need to ensure that the heavy metal of the local alien soil reaches the standard, otherwise, the food chain safety is influenced, and meanwhile, the modified ardealite land-making utilization is feasible on the premise that the alien soil quality is ensured.

Description

Technical Field

[0001] The present invention relates to the technical field of soil improvement, and in particular to a method for detecting the influence of soil modified by phosphorus chemical solid waste on crops. Background Art

[0002] The phosphorus chemical industry is huge in scale and is a pillar industry for the development of my country's national economy. In the phosphorus chemical production process, tens of millions of tons of industrial solid wastes such as phosphorus tailings and phosphogypsum are generated every year. They are basically in a saturated or overloaded storage state, which not only occupies a large amount of land resources, but also invisibly increases the operating costs of enterprises and affects the economic benefits of enterprises. These solid wastes also contain a variety of harmful impurities, and the storage is very likely to cause pollution to the atmosphere, water systems and soil. Accelerating the research and development of core technologies for the utilization of phosphorus chemical solid wastes, making full use of elements such as P and Mg and their special physical and chemical properties, turning waste into treasure, and realizing resource recycling have gradually attracted widespread attention from the public. At present, the main ways to utilize phosphorus tailings and phosphogypsum are mainly to fill mine goafs, produce building materials and produce fertilizers for agricultural production. There are many reports showing that the components of these phosphorus chemical solid wastes contain many elements required for crop growth, which can promote crop quality and yield, but also contain some polluting elements, which can enter crops and human bodies through the food chain, and ultimately endanger human health. As a typical province with a large output of solid waste from the phosphorus chemical industry in my country, Yunnan Province has an urgent need to explore more ways to utilize solid waste. By selecting phosphogypsum and phosphate tailings, the main typical solid waste from the phosphorus chemical industry in Yunnan, for soil utilization, the effects of this solid waste soil on increasing crop yields and improving quality, as well as its safety, were studied, which will help promote the resource utilization of solid waste from the phosphorus chemical industry and safe production of crops.

[0003] Rice is the main food crop in my country and is of great significance to ensuring food security. Fresh corn has a high nutritional value and health value, and its economic benefits are becoming more and more significant. The total scale of fresh corn planting in Yunnan Province has reached 1.23 million mu per season, making it one of the main fresh corn producing areas in my country. Potato is the fourth most important food crop in the world. The potato planting area in Yunnan Province accounts for 10% of the total potato area in the country, ranking fifth for many years. Buckwheat is a coarse grain rich in nutrients. It is loved by people for its high nutritional value and certain medicinal value. These crops are widely planted in Yunnan, and the research on their planting has reference value. Therefore, this study is based on the agricultural utilization of solid waste from phosphorus chemical industry, combined with the characteristics of essential plant nutrients contained in solid waste from phosphorus chemical industry, and attempts to use phosphogypsum and phosphate tailings for modified land reclamation, study the effects of land reclamation soil on crop growth and quality, evaluate the safety of phosphogypsum land reclamation soil and agricultural products, and further explore the potential of solid waste from phosphorus chemical industry for artificial land reclamation, in order to provide a reference for the safe utilization of solid waste from phosphorus chemical industry in the agricultural field.

[0004] Phosphogypsum and phosphate tailings are industrial solid wastes generated in the production process of phosphorus chemical industry. With the rapid development of phosphate fertilizer industry, their emission and stockpiling volume have been increasing dramatically, which restricts the sustainable development of phosphorus chemical industry. How to realize the resource utilization of both is an urgent problem to be studied and solved. Phosphogypsum and phosphate tailings contain a large number of elements required for plant growth, and the large area of ​​rocky desertification in Yunnan that has not been effectively utilized provides rich raw materials and vast space for artificial land reclamation. Therefore, this study is based on the agricultural utilization of these two solid wastes, and attempts to modify and reclaim land in unused land. This will be a new way to improve the resource utilization rate of solid wastes in phosphorus chemical industry and increase arable land. In order to find out the application effect and verify the feasibility of using two solid waste resources as modified artificial land, this study conducted three positioning tests, set up two land-making processes, namely, layered process and integrated process, and set three ratios in the integrated process. Corn, rice, potato and buckwheat were planted on the modified substrate to investigate the effects of artificial soil under different processes and ratios on crop growth, yield, nutritional quality and the absorption and transport of heavy metal elements Pb, Cd, As, Hg and Hg. The main conclusions are as follows:

[0005] The soil created by phosphogypsum with different processes and proportions has a significant effect on promoting the growth and yield of corn, rice, potato and buckwheat, which increased by 12.71% to 19.34%, 9.75%, 107.23% to 110.84% ​​and 0.71% to 130.63% respectively compared with the control, indicating that phosphogypsum has improved the fertility of the local red soil as the guest soil. However, the soil created by phosphorus tailings affected the growth and yield of corn, and the corn yield decreased by 5.84% to 6.47% compared with the control guest soil.

[0006] Soil reclaimed from different solid wastes has the effect of improving the nutritional quality of crops. Compared with the control, the protein, vitamin C and soluble total sugar contents of corn grains grown by the two phosphogypsum processes and the integrated phosphate tailings process increased by 16.79%-29.74%, 19.15%-24.47% and 36.64%-52.19%, respectively; the protein content of the edible parts of potatoes, rice and buckwheat planted in the phosphogypsum-reclaimed soil increased significantly by 0.69%-10.66, 13.01% and 5.55%-6.15%, respectively, compared with the control.

[0007] The edible safety of crops in the three study areas was evaluated using the National Food Safety Standard Limits of Contaminants in Food (GB2762-2022). The corn kernels in the Anning study area met the edible standards; although the Pb and Cd contents in the edible parts of potatoes in the Dongchuan test area were reduced by 58.33% to 76.23% compared with the control, they still exceeded the national standard limits. The Pb and Cr contents in the edible parts of rice exceeded the limits by 2.6 and 3.4 times, respectively; the Pb content in the edible parts of buckwheat in the Xuanwei test area exceeded the limits by 1.5 to 7.25 times. The Feed Hygiene Standard (GB13078-2017) was used to evaluate the feeding safety of corn and rice, and it was found that the Cr content in the leaves of corn and the stems and leaves of the aboveground parts of rice was reduced by 2.70% to 44.12% and 4.05% compared with the control, exceeding the national standard limits.

[0008] The ability of the non-edible parts of the four crops (roots, stems and leaves) to enrich heavy metals was stronger than that of the edible parts (grains and tubers). The BCF and TF of the edible parts (core-grains, aboveground-grains, roots-tubers, and aboveground-grains) were all less than 1, indicating low ability to enrich and transport heavy metals. The heavy metal content in the edible parts of the four crops was correlated with the heavy metal content in the soil, and the correlation was different for different crops.

[0009] The soil artificially reclaimed from phosphorus chemical solid waste can generally meet the requirements for the normal growth and development of crops such as corn, potato, buckwheat, and rice. The soil reclaimed using phosphogypsum and phosphate tailings can meet the heavy metal standards for planting corn and can be applied to agricultural production. The rice planted in paddy fields reclaimed using phosphogypsum and the potatoes and buckwheat planted in dry land must first ensure that the heavy metal standards in the local soil meet the standards, otherwise it will affect the safety of the food chain. Summary of the invention

[0010] The present invention provides a method for detecting the impact of soil modified by phosphorus chemical solid waste on crops, so as to solve the problems raised in the above-mentioned background technology.

[0011] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0012] A method for detecting the impact of soil modified by phosphorus chemical solid waste on crops, comprising the following steps:

[0013] Step 1: Select the experimental raw materials: The raw materials mainly include phosphogypsum, phosphate tailings and arable soil from local unused land. The phosphogypsum raw materials used for land reclamation are washed 2 to 3 times by the factory's water washing equipment before leaving the factory to reduce the concentration of harmful elements. The washed phosphogypsum is then modified by adding about 0.4% to 0.6% of a modifying agent to adjust the pH value of the phosphogypsum and fix the fluoride content in the phosphogypsum. After fully mixing, the modified phosphogypsum is piled up for 3 to 5 days for full reaction to obtain the modified phosphogypsum. The experiment uses two land reclamation processes, namely the layered reconstruction process (A) and the integrated land reclamation process (B);

[0014] Step 2: Regional test design, including the following: test area S21, test area S22 and test area S23;

[0015] Step 3: Sample collection and analysis test, including the following: S31: Sample collection and preparation; S32: Crop yield statistical method; S33: Crop heavy metal content and quality determination method;

[0016] Step 4: Data processing and statistics: Excel 2021 and SPSS25 software were used to perform statistical analysis on the data, and Origin 2021 software was used to draw charts. The data obtained from the experiment were all averaged three times, and the comparison of the averages was performed using the least significant difference method (ANOVE). The data in the charts were expressed as mean ± standard deviation (M ± SD), and the significant difference level was P < 0.05;

[0017] Step 5: Results and analysis: The soil artificially reclaimed from phosphorus chemical solid waste can generally meet the requirements of normal growth and development of crops such as corn, potato, buckwheat, and rice. Comprehensively considering the impact of phosphogypsum artificial soil on crop growth, it is believed that the A (layered) process is better than the B (integrated) process between the two processes; combined with the content of five heavy metals in crops, it is found that the heavy metal content of corn planted using phosphogypsum and phosphate tailings reclaimed soil meets the standards and can be applied to agricultural production. Rice planted in paddy fields reclaimed from phosphogypsum and potatoes and buckwheat planted in dry land first need to ensure that the heavy metal content of the local imported soil meets the standards, otherwise it will affect the safety of the food chain. This also shows that the utilization of modified phosphogypsum for land reclamation is feasible under the premise of ensuring the quality of the imported soil.

[0018] Preferably, the test area S21 is divided into the following steps:

[0019] S211. Test site overview: The test site is located at (24°81′N, 102°37′E), 2215m above sea level, with an average annual temperature of 14.7℃ and an average annual precipitation of 876.48mm.

[0020] S212. Test materials: Two types of solid waste from the phosphorus chemical industry and soil were selected as raw materials. The solid waste raw materials were phosphogypsum and phosphorus tailings. The guest soil was the zonal arable layer soil (0-20 cm) distributed in the unused land near the test site. The test crop was fresh glutinous corn, and the corn variety was the main local variety.

[0021] S213, Experimental design: The experimental area is about 1000m 2 Two land reclamation processes, A and B, were used. The pollutant content of each land reclamation process was in compliance with (GB 15618-2018), and the background value of heavy metal elements in the control soil was normal; there were five treatments in total, each with 160m 2 , 1.5m interval zones were set between different treatments;

[0022] For corn planting, double-row planting is adopted according to local planting habits, with a row spacing of 45cm×55cm. Before corn sowing, 800kg / mu of ecological organic fertilizer is spread to fertilize the soil (SOM≥30%, N+P2O5+K2O≥4%). During the crop growth period, irrigation, weeding and pest control are carried out according to normal field operation methods. During the corn tasseling period, 50kg / mu of urea is applied.

[0023] Preferably, the test area S22 is divided into the following steps:

[0024] S221. Overview of the test site: The test site is located at (26°13′N, 103°8′E), with an altitude of 1583.8m, an average annual temperature of 20.5℃, and an annual precipitation of 650mm, which is suitable for growing crops such as corn and rice;

[0025] S222. Test materials: Phosphogypsum and soil were used as raw materials. The guest soil was the zonal arable soil (0-20 cm) distributed in the unused land near the test site. The test crops were rice and potatoes, both of which were the main varieties grown locally.

[0026] S223. Experimental design: The experimental dry land used two land reclamation processes, A and B, and the paddy field used process B. There were three treatments in the dry land, and potatoes were planted in double rows according to local planting habits, with a row spacing of 35cm×60cm. There were two treatments in the paddy field, and rice was planted with a row spacing of 25cm×25cm. The pollutant content of each land reclamation treatment was in compliance with (GB15618-2018), and the background value of heavy metal elements in the control soil was normal.

[0027] Before sowing rice, spread 300kg / mu and 50kg / mu of bio-organic fertilizer (SOM ≥ 70%) and ternary compound fertilizer (N: P2O5: K2O = 15:15:15) to fertilize the soil. Before sowing potatoes, spread 80kg / mu of ternary compound fertilizer (N: P2O5: K2O = 16:7:12) to fertilize the soil. During the growth period of crops, irrigation, weeding and pest control are carried out according to routine field operations.

[0028] Preferably, the test area S23 is divided into the following steps:

[0029] S231. Test site overview: The test site is located at (26°7′N, 104°7′E), with an altitude of 1989.9m, an average annual temperature of 13.4℃, and an annual precipitation of 935mm;

[0030] S232. Test materials: Phosphogypsum and soil were used as raw materials. The guest soil was the zonal arable soil (0-20 cm) distributed locally near the test site. The test crop was buckwheat, which is the main local variety.

[0031] S233, Experimental design: The experimental area is about 800m 2 , using two land reclamation processes, A and B, with a total of five treatments, each with 120m 2 A 1.5m interval zone was set between different treatments. The pollutant content of each land treatment was in compliance with (GB15618-2018), and the background value of heavy metal elements in the control soil was normal.

[0032] Before sowing buckwheat, spread 300 kg of biological organic fertilizer (organic matter content ≥ 70%) and 50 kg of triple compound fertilizer (N: P2O5: K2O = 15:15:15) per mu to fertilize the soil. During the growth period of the crop, irrigation, weeding and pest control should be carried out according to routine field operations.

[0033] Preferably, the S31: Sample collection and preparation: Plant samples are collected by five-point sampling method, and representative plants are selected. Five whole plants of corn, rice and potato plants are collected from each plot, and buckwheat plants are collected at 1m 2 Five points were collected in each plot of the sample area, and the growth indicators such as plant height of the selected plants were measured respectively, and the number of plants was counted. After being brought back to the laboratory, the plant samples were divided into multiple parts according to their nutritional organs. Metal utensils were avoided in the preparation process. They were first rinsed with pure water and then washed with deionized water. After air-drying, they were weighed and the fresh weight was recorded. Then, large pieces of plant samples were cut into small pieces with a quartz knife and put into a mesh bag. A part of the fresh samples was kept for determining quality indicators, and the remaining samples were fixed in an oven at 105°C for 30 minutes, then adjusted to 65°C for drying until the mass was constant. After determining the dry mass, they were crushed with a grinder and passed through a 100-mesh nylon mesh sieve and bagged for testing.

[0034] Preferably, the S32: crop yield statistical method: before collecting plant samples, measure various growth indicators (plant height, stem thickness, etc.) of various crops, the plant height, leaf length, leaf width, etc. of the plant are measured with a tape measure, the stem thickness is measured with a vernier caliper, and the fresh weight is measured with an electronic balance. Then, after the whole plant sample is collected, it is put into a net bag and immediately brought back to the laboratory. The potato tuber fresh weight is weighed to calculate the theoretical per-acre yield of each plot. Corn, rice and buckwheat are threshed, dried, and weighed for dry weight. Finally, the theoretical per-acre yield of each plot is calculated for analyzing the crop yield-increasing effect.

[0035] Preferably, the step 4 comprises:

[0036] BCF:

[0037] The bioaccumulation factor (BCF) is an important indicator of heavy metal accumulation in crops. It is used to evaluate the accumulation capacity of various parts of crops for heavy metals. The larger the BCF, the stronger its ability to accumulate heavy metals. When the BCF is greater than 1, it indicates that the crops have a strong accumulation capacity for heavy metals. The calculation formula is:

[0038]

[0039] In the formula, BCFi is the enrichment coefficient of each heavy metal element in the i part of the test crop, Ci is the heavy metal content in the i part of the test crop, and Cs is the heavy metal content in the corresponding rhizosphere soil;

[0040] Transfer Factor (TF):

[0041] The transport coefficient indicates the ability of heavy metal transport and distribution between various parts of crops. The larger the TF, the stronger its ability to transport heavy metals. The calculation formula is:

[0042]

[0043] Where TF 下部位-上部位 TF and C are the heavy metal contents in each nutritional part of the test crops from the lower part to the upper part, respectively.

[0044] Due to the adoption of the above technical solution, the present invention has the following technical advances compared with the prior art:

[0045] 1. The present invention provides a method for detecting the influence of soil modified by phosphorus chemical solid waste on crops. The soil modified by phosphogypsum with different processes and proportions has obvious effects on promoting the growth and yield of corn, rice, potato and buckwheat. Compared with the control, the yields are increased by 12.71% to 19.34%, 9.75%, 107.23% to 110.84% ​​and 0.71% to 130.63%, respectively, indicating that phosphogypsum improves the fertility of the local red soil as the guest soil; while the soil modified by phosphorus tailings affects the growth and yield of corn. Compared with the control guest soil, the corn yield is reduced by 5.84% to 6.47%.

[0046] 2. The present invention provides a method for detecting the impact of soil modified by phosphorus chemical solid waste on crops. The soil modified by solid waste has the effect of improving the nutritional quality of crops. Compared with the control, the protein, vitamin C and soluble total sugar contents of corn grains planted by the two phosphogypsum processes and the integrated phosphate tailings process are increased by 16.79% to 29.74%, 19.15% to 24.47% and 36.64% to 52.19%, respectively; the protein contents of the edible parts of potatoes, rice and buckwheat planted in the phosphogypsum soil are significantly increased by 0.69% to 10.66%, 13.01% and 5.55% to 6.15%, respectively, compared with the control.

[0047] 3. The present invention provides a method for detecting the impact of soil modified by phosphorus chemical solid waste on crops. The edible safety of crops in the three study areas was evaluated using (GB2762-2022). The corn kernels met the edible standards. Although the Pb and Cd contents in the edible parts of potatoes were reduced by 58.33% to 76.23% compared with the control, they still exceeded the national standard limits. The Pb and Cr contents in the edible parts of rice exceeded the limits by 2.6 and 3.4 times, respectively. The Pb content in the edible parts of buckwheat exceeded the limits by 1.5 to 7.25 times. The feeding safety of corn and rice was evaluated using (GB13078-2017). It was found that the Cr contents in the leaves of corn and the stems and leaves of the aboveground parts of rice were reduced by 2.70% to 44.12% and 4.05% compared with the control, exceeding the national standard limits.

[0048] 4. The present invention provides a method for detecting the impact of soil modified by phosphorus chemical solid waste on crops. The ability of the non-edible parts of four crops (roots, stems and leaves) to enrich heavy metals is stronger than that of the edible parts (grains and tubers). The BCF and TF of the edible parts (core-grains, aboveground parts-grains, roots-tubers, and aboveground parts-grains) are all less than 1, and the ability to enrich and transport heavy metals is relatively low. The heavy metal content in the edible parts of the four crops has a certain correlation with the heavy metal content in the soil, and the correlation is different for different crops.

[0049] 5. The present invention provides a method for detecting the impact of soil modified by phosphorus chemical solid waste on crops. The soil artificially reclaimed by phosphorus chemical solid waste can generally meet the requirements of normal growth and development of crops such as corn, potato, buckwheat, and rice. Taking into account the impact of artificial soil made of phosphogypsum on crop growth, it is believed that process A (layered) is better than process B (integrated) between the two processes. Combined with the content of five heavy metals in crops, it is found that the heavy metal content of corn planted using phosphogypsum and soil reclaimed by phosphate tailings meets the standards and can be applied to agricultural production. Rice planted in paddy fields reclaimed by phosphogypsum and potatoes and buckwheat planted in dry land first need to ensure that the heavy metal content of the local imported soil meets the standards, otherwise it will affect the safety of the food chain. This also shows that the utilization of modified phosphogypsum for land reclamation is feasible under the premise of ensuring the quality of the imported soil. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 This is a schematic diagram of a comprehensive utilization approach for phosphogypsum of the present invention;

[0051] Figure 2 It is the technical roadmap of the present invention;

[0052] Figure 3 Schematic diagram of different land-making processes of the present invention;

[0053] Figure 4 Schematic diagram of the contents of Pb, Cd, Cr, As and Hg in various parts of corn according to the present invention;

[0054] Figure 5 It is a schematic diagram of the correlation between corn kernels and soil heavy metal content of the present invention;

[0055] Figure 6 It is a schematic diagram of the enrichment coefficients of Pb, Cd, Cr, As and Hg in various parts of corn according to the present invention;

[0056] Figure 7 It is a schematic diagram of the transport coefficients of Pb, Cd, Cr, As and Hg between various parts of corn according to the present invention;

[0057] Figure 8 It is a schematic diagram of the contents of Pb, As, Cd, Cr and Hg in various parts of potatoes of the present invention;

[0058] Fig. 9 is a schematic diagram of the correlation between potato tubers and heavy metal content in soil according to the present invention;

[0059] Fig.10 It is a schematic diagram of the enrichment coefficients of Pb, As, Cd, Cr and Hg in various parts of potatoes according to the present invention;

[0060] Fig.11 Schematic diagram of the transport coefficients of Pb, As, Cd, Cr and Hg between various parts of potatoes of the present invention;

[0061] Fig.12 Schematic diagram of the contents of Pb, As, Cd, Cr and Hg in various parts of rice according to the present invention;

[0062] Fig.13 It is a schematic diagram of the correlation between rice grains and heavy metal content in soil according to the present invention;

[0063] Fig.14 It is a schematic diagram of the enrichment coefficients of Pb, As, Cd, Cr and Hg in various parts of rice according to the present invention;

[0064] Fig.15 It is a schematic diagram of the transport coefficients of Pb, As, Cd, Cr and Hg between various parts of rice according to the present invention;

[0065] Fig.16 Schematic diagram of the contents of Pb, As, Cd, Cr and Hg in various parts of buckwheat according to the present invention;

[0066] Fig.17 It is a schematic diagram of the correlation between buckwheat seeds and the heavy metal content in soil according to the present invention;

[0067] Fig.18 It is a schematic diagram of the enrichment coefficients of Pb, As, Cd, Cr and Hg in various parts of buckwheat according to the present invention;

[0068] Fig.19 It is a schematic diagram of the transport coefficients of Pb, As, Cd, Cr and Hg between various parts of buckwheat according to the present invention. DETAILED DESCRIPTION

[0069] In order to make the technical means, creative features, objectives and effects achieved by the present invention easy to understand, the present invention is further explained below in conjunction with specific implementation methods.

[0070] like Figure 1-Figure 19 As shown, a method for detecting the impact of soil modified by phosphorus chemical solid waste on crops includes the following steps:

[0071] Step 1: Select the experimental raw materials: The raw materials mainly include phosphogypsum, phosphate tailings and arable soil from local unused land. The phosphogypsum raw materials used for land reclamation are washed 2 to 3 times by the factory's water washing equipment before leaving the factory to reduce the concentration of harmful elements. The washed phosphogypsum is then modified by adding about 0.4% to 0.6% of a modifying agent to adjust the pH value of the phosphogypsum and fix the fluoride content in the phosphogypsum. After fully mixing, the modified phosphogypsum is obtained by stacking for 3 to 5 days for full reaction. The experiment uses two land reclamation processes, namely the layered reconstruction process (A) and the integrated land reclamation process (B). Figure 3 As shown;

[0072] Step 2: Regional test design, including the following: test area S21, test area S22 and test area S23;

[0073] Step 3: Sample collection and analysis test, including the following: S31: Sample collection and preparation; S32: Crop yield statistical method; S33: Crop heavy metal content and quality determination method;

[0074] Step 4: Data processing and statistics: Excel 2021 and SPSS25 software were used to perform statistical analysis on the data, and Origin 2021 software was used to draw charts. The data obtained from the experiment were all averaged three times, and the comparison of the averages was performed using the least significant difference method (ANOVE). The data in the charts were expressed as mean ± standard deviation (M ± SD), and the significant difference level was P < 0.05;

[0075] Step 5: Results and analysis: The soil artificially reclaimed from phosphorus chemical solid waste can generally meet the requirements of normal growth and development of crops such as corn, potato, buckwheat, and rice. Comprehensively considering the impact of phosphogypsum artificial soil on crop growth, it is believed that the A (layered) process is better than the B (integrated) process between the two processes; combined with the content of five heavy metals in crops, it is found that the heavy metal content of corn planted using phosphogypsum and phosphate tailings reclaimed soil meets the standards and can be applied to agricultural production. Rice planted in paddy fields reclaimed from phosphogypsum and potatoes and buckwheat planted in dry land first need to ensure that the heavy metal content of the local imported soil meets the standards, otherwise it will affect the safety of the food chain. This also shows that the utilization of modified phosphogypsum for land reclamation is feasible under the premise of ensuring the quality of the imported soil.

[0076] The test area S21 is divided into the following steps:

[0077] S211. Test site overview: The test site is located at (24°81′N, 102°37′E), 2215m above sea level, with an average annual temperature of 14.7℃ and an average annual precipitation of 876.48mm.

[0078] S212. Test materials: Two types of solid waste from the phosphorus chemical industry and soil were selected as raw materials. The solid waste raw materials were phosphogypsum and phosphorus tailings, and the guest soil was the zonal arable layer soil (0-20 cm) distributed in the unused land near the test site. The basic physical and chemical properties of the raw materials and the mass concentration of heavy metals are shown in Table 1. The test crop was fresh glutinous corn, and the corn variety was the main local variety;

[0079] Table 1 Main physical and chemical properties and heavy metal content of the tested raw materials

[0080]

[0081] S213, Experimental design: The experimental area is about 1000m 2, two land reclamation processes A and B were used, and the specific processes and proportions are shown in Table 2. The basic physical and chemical properties of the soil in each treatment are shown in Table 3. The pollutant content of each land reclamation treatment complies with (GB 15618-2018), and the background value of heavy metal elements in the control soil is normal; there are five treatments in total, each with 160m 2 , 1.5m interval zones were set between different treatments;

[0082] For corn planting, double-row planting is adopted according to local planting habits, with a row spacing of 45cm×55cm. Before corn sowing, 800kg / mu of ecological organic fertilizer is spread to fertilize the soil (SOM≥30%, N+P2O5+K2O≥4%). During the crop growth period, irrigation, weeding and pest control are carried out according to normal field operation methods. During the corn tasseling period, 50kg / mu of urea is applied.

[0083] Table 2 Experimental treatment and design

[0084] Processing number Land creation technology and ratio (mass ratio) CK 100% local soil ZA Phosphate tailings layered reconstruction process A ZB Integrated land reclamation process B, phosphate tailings: imported soil = 5:5 GA Phosphogypsum layered reconstruction process A GB Integrated land reclamation process B, phosphogypsum: foreign soil = 5:5

[0085] Table 3 Basic physical and chemical properties of soils from different land reclamation

[0086]

[0087] The test area S22 is divided into the following steps:

[0088] S221. Overview of the test site: The test site is located at (26°13′N, 103°8′E), with an altitude of 1583.8m, an average annual temperature of 20.5℃, and an annual precipitation of 650mm, which is suitable for growing crops such as corn and rice;

[0089] S222. Test materials: Phosphogypsum and soil were used as raw materials. The guest soil was the zonal arable soil (0-20 cm) distributed in the unused land near the test site. The basic physical and chemical properties of the raw materials and the mass concentration of heavy metals are shown in Table 4. The test crops were rice and potatoes, both of which were the main varieties grown locally.

[0090] Table 4 Main physical and chemical properties and heavy metal content of the tested raw materials

[0091]

[0092] S223. Experimental design: The experimental dry land used two land reclamation processes, A and B, and the paddy field used process B. The specific ratios and treatment areas are shown in Table 5. There were three treatments in the dry land, and potatoes were planted. According to local planting habits, double-row planting was adopted, with a row spacing of 35cm×60cm. There were two treatments in the paddy field, and rice was planted with a row spacing of 25cm×25cm. The basic physical and chemical properties of the soil in each treatment are shown in Table 6. The pollutant content of each land reclamation treatment was in accordance with (GB15618-2018), and the background value of heavy metal elements in the control soil was normal.

[0093] Before sowing rice, spread 300kg / mu and 50kg / mu of bio-organic fertilizer (SOM ≥ 70%) and ternary compound fertilizer (N: P2O5: K2O = 15:15:15) to fertilize the soil. Before sowing potatoes, spread 80kg / mu of ternary compound fertilizer (N: P2O5: K2O = 16:7:12) to fertilize the soil. During the growth period of crops, irrigation, weeding and pest control are carried out according to routine field operations.

[0094] Table 5 Experimental treatment and design

[0095]

[0096] Note: “—” in the table means not detected.

[0097] Table 6 Basic physical and chemical properties of soils from different land reclamation

[0098]

[0099] The test area S23 is divided into the following steps:

[0100] S231. Test site overview: The test site is located at (26°7′N, 104°7′E), with an altitude of 1989.9m, an average annual temperature of 13.4℃, and an annual precipitation of 935mm;

[0101] S232. Test materials: Phosphogypsum and soil were used as raw materials. The guest soil was the zonal arable soil (0-20 cm) distributed locally near the test site. The basic physical and chemical properties and heavy metal mass concentrations of the raw materials are shown in Table 7. The test crop was buckwheat, which is the main variety grown locally;

[0102] Table 7 Main physical and chemical properties and heavy metal content of the tested raw materials

[0103]

[0104] S233, Experimental design: The experimental area is about 800m 2 , using two land reclamation processes, A and B, the specific processes and proportions are shown in Table 8. There are five treatments in total, each with 120m 2 , 1.5m interval zones were set between different treatments. The basic physical and chemical properties of the soil in each treatment are shown in Table 9. The pollutant content of each land reclamation treatment met the "Soil Environmental Quality Agricultural Land Soil Pollution Risk Control Standard" (GB15618-2018), and the background value of heavy metal elements in the control soil was normal.

[0105] Before sowing buckwheat, spread 300 kg of biological organic fertilizer (organic matter content ≥ 70%) and 50 kg of triple compound fertilizer (N: P2O5: K2O = 15:15:15) per mu to fertilize the soil. During the growth period of the crop, irrigation, weeding and pest control should be carried out according to routine field operations.

[0106] Table 8 Experimental treatment and design

[0107] Processing Name Land creation technology and ratio (mass ratio) CK 100% local soil GA Layered Reconstruction Process A GB1 Integrated land reclamation process B, phosphogypsum: foreign soil = 5:5 GB2 Integrated land reclamation process B, phosphogypsum: imported soil = 5.5:4.5 GB3 Integrated land reclamation process B, phosphogypsum: imported soil = 6.5:3.5

[0108] Table 9 Basic physical and chemical properties of soils from different land reclamation

[0109]

[0110] S31: Sample collection and preparation: Plant samples were collected using the five-point sampling method, and representative plants were selected. Five whole plants of corn, rice and potato plants were collected from each plot, and buckwheat plants were collected at 1m 2 Five points were collected in each plot of the sample area, and the growth indicators such as plant height of the selected plants were measured respectively, and the number of plants was counted. After being brought back to the laboratory, the plant samples were divided into multiple parts according to their nutritional organs. Metal utensils were avoided in the preparation process. They were first rinsed with pure water and then washed with deionized water. After air-drying, they were weighed and the fresh weight was recorded. Then, large pieces of plant samples were cut into small pieces with a quartz knife and put into a mesh bag. A part of the fresh samples was kept for determining quality indicators, and the remaining samples were fixed in an oven at 105°C for 30 minutes, then adjusted to 65°C for drying until the mass was constant. After determining the dry mass, they were crushed with a grinder and passed through a 100-mesh nylon mesh sieve and bagged for testing.

[0111] S32: Crop yield statistical method: Before collecting plant samples, measure various growth indicators (plant height, stem thickness, etc.) of various crops. The plant height, leaf length, leaf width, etc. of the plant are measured with a tape measure, the stem thickness is measured with a vernier caliper, and the fresh weight is measured with an electronic balance. Then, after the whole plant sample is collected, it is put into a net bag and immediately brought back to the laboratory. The fresh weight of potato tubers is weighed to calculate the theoretical per-acre yield of each plot. Corn, rice and buckwheat are threshed, dried, and weighed for dry weight. Finally, the theoretical per-acre yield of each plot is calculated for analyzing the crop yield increase effect.

[0112] Methods for determining heavy metal content and quality of crops: All heavy metal analysis and crop quality analysis methods are based on national or industry standards, as shown in Tables 10 and 11.

[0113] Table 10 Crop heavy metal detection items, methods and equipment:

[0114] Heavy Metal Elements standard Testing instrument name and model Cadmium (Cd) GB5009.268-2016 Inductively coupled plasma mass spectrometer ICAPRQ, ACJ36 Mercury (Hg) GB5009.17-2021 Atomic Fluorescence Spectrometer AFS8520 Arsenic (As) GB5009.268-2016 Inductively coupled plasma mass spectrometer ICAPRQ, ACJ36 Lead (Pb) GB5009.268-2016 Inductively coupled plasma mass spectrometer ICAPRQ, ACJ36 Chromium (Cr) GB5009.268-2016 Inductively coupled plasma mass spectrometer ICAPRQ, ACJ36

[0115] Table 11 Crop quality testing items and methods:

[0116] Nutritional Information standard Soil Agrochemical Analysis Methods protein GB5009.5-2016 H2SO4-K2SO4-CuSO4-Se digestion method Vitamin C GB / T5009.82-2016 2,4-Dinitrophenylhydrazine Colorimetric Method Total soluble sugar NY / T1278-2007 Acid hydrolysis copper reduction direct titration method Soluble protein GB5009.5-2016 Coomassie Brilliant Blue G-250 staining Organic Acid GB5009.157-2016 Acid-base titration Proline GB5009.124-2016 Colorimetry

[0117] The fourth step comprises:

[0118] BCF:

[0119] The bioaccumulation factor (BCF) is an important indicator of heavy metal accumulation in crops. It is used to evaluate the accumulation capacity of various parts of crops for heavy metals. The larger the BCF, the stronger its ability to accumulate heavy metals. When the BCF is greater than 1, it indicates that the crops have a strong accumulation capacity for heavy metals. The calculation formula is:

[0120]

[0121] In the formula, BCFi is the enrichment coefficient of each heavy metal element in the i part of the test crop, Ci is the heavy metal content in the i part of the test crop, and Cs is the heavy metal content in the corresponding rhizosphere soil;

[0122] Transfer Factor (TF):

[0123] The transport coefficient indicates the ability of heavy metal transport and distribution between various parts of crops. The larger the TF, the stronger its ability to transport heavy metals. The calculation formula is:

[0124]

[0125] Where TF 下部位-上部位 TF and C are the heavy metal contents in each nutritional part of the test crops from the lower part to the upper part, respectively.

[0126] Results and analysis: Effect of corn planting on reclaimed soil:

[0127] Analysis of corn yield and biological traits under different treatments

[0128] The effects of different land reclamation treatments on maize growth traits are shown in Table 12. There were significant differences in plant height, stem diameter, leaf area, biomass, 100-grain weight and yield of the tested maize variety "Tianzi 23" under different treatments. The average yield of maize under different treatments was 9308.47 kg·hm -2, the coefficient of variation was 5.38%. Compared with CK, the yields of GA and GB increased by 19.34% and 12.71% respectively, while the yields of ZA and ZB decreased by 6.47% and 5.84% respectively compared with CK, showing ZA < ZB < CK < GB < GA. The average values of plant height, stem diameter, leaf area, biomass and 100-grain weight of maize under different treatments were 181.27 cm, 28.93 mm, 522.03 cm², 325.53 g and 26.57 g respectively, and the coefficient of variation was 4.24% - 8.90%. Compared with CK, the leaf area and biomass of GA and GB treatments were significantly increased (P < 0.05). The GA treatment increased by 27.89% and 17.33% respectively, and the GB treatment increased by 24.87% and 2.50% respectively. On the contrary, compared with CK, the plant height, biomass and 100-grain weight of ZA and ZB were significantly reduced.

[0129] Table 12 Maize biological traits and yields under different treatments:

[0130]

[0131] Note: Different lowercase letters in the same column indicate significant differences among different maize varieties (P < 0.05), the same below.

[0132] Analysis of maize nutritional quality content under different treatments: The average values of total soluble sugar, soluble protein, vitamin C, protein and proline contents in maize under different treatments were 11.94 mg·g⁻¹, 23.58 mg·g⁻¹, 1.95 mg·100g⁻¹, 4.87% and 0.03% respectively, and the coefficient of variation was 2.14% - 33.33%. Compared with CK, the total soluble sugar, vitamin C and protein of GA and GB treatments were significantly increased (P < 0.05). Among them, the GA treatment was significantly increased by 52.19%, 24.47% and 29.74% respectively, and the GB treatment was significantly increased by 36.74%, 19.15% and 25.42% respectively. The total soluble sugar and protein contents of ZB treatment were also significantly increased by 36.64% and 16.79% compared with CK. There were no significant changes in the soluble protein content and proline content of maize under all land reclamation treatments.

[0133] Table 13 Nutritional component contents in maize under different treatments:

[0134]

[0135] Analysis of heavy metal content differences in maize under different treatments: The heavy metal content in maize under different treatments was as Figure 4(Note: Different lowercase letters indicate significant differences among different treatments of the same part (P<0.05). The missing treatments in the bar graphs were not detected. The detection limits of Pb, As, Cd, Cr and Hg were <0.02, <0.002, <0.002, <0.05 and <0.003 mg·kg, respectively. -1， The same below). There were significant differences in the contents of Pb, As, Cd, Cr and Hg in various parts of the tested corn under different treatments (P<0.05). The Pb content in the roots, stems, leaves, cobs and grains of the tested corn under different treatments ranged from 7.01 to 13.50, 0.29 to 0.57, 2.61 to 3.31, 0.123 to 0.197 and 0.06 to 0.10 mg·kg, respectively. -1 The average values ​​were 10.84, 0.43, 2.84, 0.155 and 0.076 mg kg -1 The coefficient of variation was between 4.80% and 23.68%; the As content ranges were 0.752-1.330, 0.044-0.064, 0.271-0.326, 0.024-0.036, and 0.01-0.016 mg·kg -1 The average values ​​were 1.091, 0.052, 0.292, 0.031 and 0.013 mg·kg -1 , the coefficient of variation was between 3.42% and 15.38%; the Cd content ranges were 0.078-0.168, 0.045-0.066, 0.129-0.229, 0.036-0.068, and 0.01-0.024 mg·kg -1 The average values ​​were 0.120, 0.052, 0.168, 0.047 and 0.019 mg kg -1 , the coefficient of variation was between 4.76% and 23.68%; the ranges of Cr content were 20.60-41.10, 1.62-2.30, 7.91-12.50, 0.537-0.807, and 0.10-0.14 mg·kg -1 The average values ​​were 33.60, 2.196, 10.344, 0.698 and 0.124 mg·kg -1 , the coefficient of variation was between 2.60% and 14.33%; the Hg content ranges were 0.115-0.545, 0.004-0.006, 0.027-0.038, 0.007-0.016, and 0.003-0.005 mg·kg -1 The average values ​​were 0.228, 0.005, 0.032, 0.011 and 0.004 mg kg -1The coefficient of variation was between 2.19% and 20.00%. Overall, the contents of Pb, As, Cd and Hg in the edible grains of ZA, ZB, GA and GB were lower than those of CK.

[0136] Since soil heavy metal pollution can accumulate step by step through the food chain and eventually endanger human health, this study was evaluated based on the national food safety standards and feed hygiene standards. The corresponding results are shown in Table 12. In all treatments of this experiment, the contents of Pb, Cd, Cr, As and Hg in corn kernels met the limit standards in food in the National Food Safety Standard Limits of Contaminants in Food (GB2762-2022), and the maximum content level allowed in grains (Pb ≤ 0.2 mg kg -1 、Cd≤0.1mg·kg -1 、Cr≤1.0mg·kg -1 、As≤0.5mg·kg -1 and Hg≤0.02mg·kg -1 The content of Pb, Cd, As and Hg in the stems, leaves and cobs of all treated corns met the requirements of the Feed Hygiene Standard (GB13078-2017) (Pb≤30.0mg·kg -1 、As≤4.0mg·kg -1 、Cd≤1.0mg·kg -1 and Hg≤0.1mg·kg -1 The Cr content in corn leaves of all treatments ranged from 7.91 to 12.50 mg kg -1 Both exceed the requirements of GB13078-2017 (Cr≤5.0mg·kg -1 ), the Cr content in the leaves of maize treated with ZA, ZB and GA was lower than that with CK, which was shown by GA <ZA<ZB<CK<GB。

[0137] Correlation between the edible part of corn kernels and the heavy metal content in soil: There is a correlation between the heavy metal content in corn kernels and the heavy metal content in soil, such as Figure 5As shown (Note: *P≤0.05, **P≤0.01). In general, As and Hg in crops are most affected by the heavy metal content in the soil, followed by Cd and Cr. In the study area, Cd in corn kernels was significantly positively correlated with soil As (R2=0.63) and extremely significantly positively correlated with Pb (R2=0.68); Cr content in corn kernels was significantly positively correlated with soil Cd, with a correlation coefficient of 0.52; As content in corn kernels was extremely significantly positively correlated with soil As, Cr and Pb, with correlation coefficients of 0.73, 0.74 and 0.67, respectively; Hg content in corn kernels was extremely significantly negatively correlated with soil Hg, and extremely significantly positively correlated with Pb, As and Cr, with correlation coefficients of 0.70, 0.78 and 0.97, respectively. There was no obvious correlation between Pb in corn kernels and the five heavy metals in the soil.

[0138] Difference analysis of heavy metal enrichment factor (BCF) of maize under different treatments: Figure 6As shown in the figure, there were significant differences in the enrichment coefficients of each part of the tested corn under different treatments (P<0.05). The enrichment coefficients (3-3a) of Pb in the roots, stems, leaves, cobs, and grains of the tested corn under different treatments were 0.048-0.267, 0.002-0.005, 0.013-0.054, 0.001-0.003, and 0.0001-0.0007, respectively, with average values ​​of 0.108, 0.004, 0.027, 0.001, and 0.001, respectively, and the coefficient of variation was 4. 72%~28.37%; the enrichment coefficients of As (3-3b) ranged from 0.03~0.26, 0.002~0.008, 0.009~0.056, 0.001~0.005, 0.0005~0.002, with average values ​​of 0.103, 0.004, 0.026, 0.003, 0.001, and coefficients of variation of 3.11%~15.63%; the enrichment coefficients of Cr ... The ranges of the numbers (3-3d) were 0.416-1.027, 0.029-0.073, 0.114-0.398, 0.009-0.015, 0.001-0.004, with average values ​​of 0.620, 0.044, 0.206, 0.013, 0.002, and coefficients of variation of 2.93%-15.12%. The ranges of the enrichment coefficients (3-3e) of Hg were 0.15 The accumulation rates of Pb, As, Cr and Hg in various parts were as follows: grain < cob < stem < leaf < root. The enrichment coefficients (3-3c) of Cd ranged from 0.166 to 0.873, 0.084 to 0.380, 0.253 to 0.954, 0.080 to 0.294, and 0.040 to 0.100, with average values ​​of 0.477, 0.209, 0.662, 0.179, and 0.067, respectively, and coefficients of variation of 4.54% to 21.13%. The Cd enrichment capacity of each part was as follows: grain < cob < stem < root < leaf. The BCF of the grains of the edible parts of corn in each treatment was <1, and the enrichment capacity of corn grains for heavy metals was weak.

[0139] Difference analysis of heavy metal transport coefficient (TF) of maize under different treatments

[0140] Heavy metal transport coefficients of maize under different treatments Figure 7As shown in the figure, there were significant differences in the transport coefficients among the various parts of the tested maize under different treatments (P<0.05). The TF root-stem, TF stem-leaf, TF stem-cob, and TF cob-grain (3-4a) of Pb in the tested maize under different treatments ranged from 0.030 to 0.056, 4.746 to 9.055, 0.220 to 0.575, and 0.461 to 0.517, respectively, with average values ​​of 0.040, 7.019, 0.391, and 0.494, respectively, and the coefficient of variation was 7.5% to 29.15%; the A of each transport part of maize The transport coefficients of s (3-4b) ranged from 0.033 to 0.064, 4.249 to 6.515, 0.451 to 0.758, and 0.381 to 0.460, with average values ​​of 0.049, 5.755, 0.609, and 0.425, respectively, and the coefficient of variation was 8.16% to 12.64%. The transport coefficients of Cd in each transport part of corn (3-4c) ranged from 0.394 to 0.582, 2.503 to 4.0 64, 0.632-1.401, 0.290-0.487, with average values ​​of 0.463, 3.261, 0.928, and 0.411, respectively, with coefficients of variation of 7.21% to 22.63%; the transport coefficients (3-4d) of Cr in each transport part of corn were 0.055-0.112, 3.840-7.038, 0.261-0.499, and 0.149-0.210, with average values ​​of 0.07 3, 4.899, 0.331, and 0.185, with a coefficient of variation of 7.35% to 23.78%; the transport coefficients (3-4e) of Hg in various transport parts of corn ranged from 0.011 to 0.052, 4.802 to 9.833, 1.305 to 4.522, and 0.334 to 0.347, with average values ​​of 0.049, 5.755, 0.609, and 0.425, with a coefficient of variation of 8.16% to 12.24%. In this study, the transport coefficients of As, Cd, Cr, and Hg in various parts of corn were as follows: root-stem < cob-grain < stem cob < stem-leaf. Except for the stem-leaf part, which was greater than 1, the transport coefficients of Pb, As, Cd, Cr, and Hg in other parts were less than 1. In addition, the average transport coefficients of Pb, As, Cd, Cr, and Hg in the stem-leaf part under each reclamation treatment were lower than those in CK.

[0141] Effect of soil cultivation on potato planting:

[0142] Analysis of potato yield and biological traits under different treatments: The potato yield and biological traits under different treatments are shown in Table 14. There are significant differences in plant height, stem diameter, single potato weight, number of tubers, biomass, and potato yield under the two land reclamation treatments. The average potato yield under different treatments is 28,666.67 kg·hm-2, and the coefficient of variation is 4.18%. Compared with CK, the yields of GA and GB increased significantly by 107.23% and 110.84% respectively, showing CK < GA < GB; the average values of plant height, stem diameter, single potato weight, biomass, and number of tubers of potatoes under different treatments are 48.33 cm, 8.30 mm, 66.25 g, 153.88 g·plant-1, and 8.33 respectively, and the coefficient of variation is 5.46% - 18.77%. Compared with CK, the plant height, single potato weight, biomass, and number of tubers of GA and GB increased significantly (P < 0.05). Among them, the GA treatment increased significantly by 42.11%, 18.72%, 34.74%, and 86.60% respectively, and the GB treatment increased significantly by 39.47%, 40.50%, 63.83%, and 93.40% respectively. Among them, the GA treatment has the best effect on improving potato plant height, and the GB treatment has the best effect on improving single potato weight, biomass, and number of tubers of potatoes.

[0143] Table 14 Biological traits and yields of potatoes under different treatments

[0144]

[0145]

[0146] Analysis of the content of potato nutritional quality under different treatments:

[0147] The content of potato nutritional quality under different land reclamation treatments is shown in Table 15. The protein content of potatoes varies from 7.22% to 7.99% under the two land reclamation treatments. Compared with CK, the GA and GB treatments both significantly increased the protein content of potatoes. Among them, the GA treatment has the best effect on increasing the potato content, and the protein content is 7.99%, which is significantly increased by 10.66% compared with CK; the proline content of potatoes varies from 0.06% to 0.10% under all land reclamation treatments. Among them, the GB treatment has the best effect on increasing the proline content of potatoes, which is significantly increased by 66.67% compared with CK; there are no significant changes in the soluble protein content, vitamin C content, and soluble total sugar content of potatoes under all land reclamation treatments.

[0148] Table 15 Contents of nutritional components in potatoes under different treatments

[0149]

[0150] Analysis of the differences in heavy metal contents of potatoes under different treatments: The heavy metal contents of potatoes under different treatments are as Figure 8As shown in the figure, there were significant differences in the contents of Pb, As, Cd, Cr and Hg in various parts of the tested potatoes under different treatments (P<0.05). The Pb content (3-5a) in the root, aerial part and tuber of the tested potatoes under different treatments ranged from 23.94 to 26.77, 5.40 to 7.98 and 0.20 to 0.38 mg·kg -1 The average values ​​were 25.37, 6.48, and 0.27 mg·kg -1 The coefficient of variation was between 2.10% and 5.97%; the As content (3-5b) ranged from 0.900 to 5.200, 0.504 to 0.668, and 0.009 to 0.015 mg·kg -1 The average values ​​were 2.258, 0.573, and 0.012 mg·kg -1 The coefficient of variation was between 2.28% and 9.33%; the Cd content (3-5c) ranged from 5.133 to 8.077, 3.540 to 7.720, and 0.244 to 0.430 mg·kg -1 The average values ​​were 5.920, 1.840, and 0.333 mg·kg -1 , the coefficient of variation was between 1.96% and 3.27%; the Cr content (3-5d) ranged from 4.55 to 7.22, 1.10 to 2.80, and 0.27 to 0.46 mg·kg -1 The average values ​​were 5.920, 1.840, and 0.333 mg·kg -1 The coefficient of variation was between 1.96% and 3.27%; the ranges of Hg content (3-5e) were 0.197-0.259, 0.164-0.186, and 0.003-0.005 mg·kg -1 The average values ​​were 0.231, 0.172, and 0.004 mg·kg -1 , the coefficient of variation ranged from 5.44% to 13.61%.

[0151] Since soil heavy metal pollution can accumulate step by step through the food chain and eventually endanger human health, this study was evaluated based on the national food safety standards and feed hygiene standards. The corresponding results are shown in Table 12. In all treatments of this experiment, the Cr, As and Hg contents in potato tubers met the limit standards in food in the National Food Safety Standard Limits of Contaminants in Food (GB2762-2022), and the maximum content level allowed in potatoes (Cr ≤ 1.0 mg kg -1 、As≤0.5mg·kg -1 and Hg≤0.02mg·kg -1 ), the Pb and Cd contents exceeded the limit standard of GB2762-2022 (Pb≤0.2mg·kg-1 and Cd≤0.1mg·kg -1 ), the Pb contents in GB and CK treatments exceeded the national standard limit by 1.2 and 1.9 times, respectively, and the Cd contents in GA, GB and CK treatments exceeded the national standard limit by 1.2, 1.2 and 2.1 times, respectively. Among them, the Cd contents in GA and GB treatments were significantly lower than those in CK, showing GB<GA<CK.

[0152] Correlation between the heavy metal content in potato tubers and soil: There is a certain correlation between the heavy metal content in potato tubers and the heavy metal content in soil, such as Fig. 9 As shown (Note: *P≤0.05, **P≤0.01). In general, Pb and As in crops are most affected by the heavy metal content in the soil, followed by Hg. In the study area, Pb in potato tubers was extremely significantly positively correlated with soil Cd and As (R2=0.88 and 0.97), and extremely significantly negatively correlated with Pb and Hg (R2=-0.94 and -0.87); As content in potato tubers was extremely significantly positively correlated with soil Pb and Hg, with correlation coefficients of 0.88 and 0.84, respectively, and extremely significantly negatively correlated with soil Cd, Cr and As content; Hg content in potato tubers was extremely significantly positively correlated with soil Pb and Hg, with correlation coefficients of 0.77 and 0.86, respectively, and extremely significantly negatively correlated with As. There was no obvious correlation between Cd and Cr in potato tubers and the five heavy metals in the soil.

[0153] Analysis of the difference of heavy metal enrichment factor (BCF) of potatoes under different treatments: Fig.10As shown, there were significant differences in the enrichment coefficients of various parts of the tested potatoes under different treatments (P<0.05). The enrichment coefficients of Pb in the root, aerial part, and tuber of the tested potatoes under different treatments (3-7a) ranged from 0.348 to 0.496, 0.087 to 0.125, and 0.003 to 0.008, respectively, with average values ​​of 0.424, 0.107, and 0.005, respectively; the enrichment coefficients of As (3-7b) ranged from 0.013 to 0.135, 0.010 to 0.014, and 0.0002 to 0.0005, respectively, with average values ​​of 0.058, 0.015, and 0.0003, respectively; the enrichment coefficients of Cd (3-7c) ranged from 15.03 to 22. 44, 9.98-21.44, 0.567-1.194, with average values ​​of 18.01, 14.28 and 0.852, respectively; the enrichment factors of Cr (3-7d) ranged from 0.067-0.087, 0.012-0.031, 0.003-0.005, with average values ​​of 0.078, 0.025 and 0.004, respectively; the enrichment factors of Hg (3-7e) ranged from 0.178-0.233, 0.124-0.204, 0.003-0.004, with average values ​​of 0.209, 0.159 and 0.004, respectively. The enrichment capacity of Pb, As, Cd, Cr and Hg in various parts showed the order of tuber < aboveground part < root. The BCF of tubers in the edible parts of potatoes in each treatment was <1, indicating that the enrichment capacity of potato tubers for heavy metals was weak.

[0154] Analysis of the difference of potato heavy metal transport coefficient (TF) under different treatments: The heavy metal transport coefficient of potato under different treatments is as follows: Fig.11As shown, there were significant differences in the transport coefficients between different parts of the tested potatoes under different treatments (P<0.05). The TF root-aerial part and TF root-tuberculate (3-8a) of Pb in the tested potatoes under different treatments ranged from 0.202 to 0.314 and 0.008 to 0.016, with average values ​​of 0.256 and 0.011, respectively; the transport coefficients of As between different parts of potatoes (3-8b) ranged from 0.105 to 0.750 and 0.002 to 0.017, with average values ​​of 0.535 and 0.011, respectively; the transport coefficients of Cd between different parts of potatoes (3-8c) ranged from 0.105 to 0.750 and 0.002 to 0.017, with average values ​​of 0.535 and 0.011, respectively. The transport coefficients of Pb, As, Cd, Cr and Hg between different parts of potato were 0.666~0.956, 0.038~0.053, and the average values ​​were 0.771 and 0.046, respectively; the transport coefficients of Cr between different parts of potato (3-8d) ranged from 0.152~0.468, 0.045~0.064, and the average values ​​were 0.325 and 0.056, respectively; the transport coefficients of Hg between different parts of potato (3-8e) ranged from 0.633~0.749, 0.015~0.021, and the average values ​​were 0.758 and 0.017, respectively. In this study, the transport coefficients of Pb, As, Cd, Cr and Hg between different parts of potato were root-tuber < root-aerial part, and the transport coefficients of Pb, As, Cd, Cr and Hg in different parts of tested potato were all less than 1, indicating that the transport capacity of potato tubers for heavy metals was weak.

[0155] Analysis of rice yield and biological traits under different treatments: The growth and yield of rice under phosphogypsum land reclamation treatment are shown in Table 16. The soil of this land reclamation has a certain promoting effect on the growth of rice. Under the phosphogypsum land reclamation treatment, the average values ​​of rice plant height, stem diameter, biomass, effective panicle, fruit setting rate and 1000-grain weight were 109.50 cm, 5.47 mm, 133.97 g·plant-1, 200,000 panicles / mu, 85.25% and 23.60 g, respectively, and the coefficient of variation was between 1.19% and 7.50%. Compared with CK, GB increased stem diameter, biomass, effective panicle, fruit setting rate and 1000-grain weight by 0.56%, 7.47%, 4.08%, 0.93% and 6.52%, respectively. Phosphogypsum land reclamation soil also has a significant effect on increasing rice yield. Compared with CK, rice yield increased by 8.82%, reaching 8299.65 kg·hm -2 .

[0156] Table 16 Rice yield and biological characteristics after phosphogypsum land reclamation treatment

[0157]

[0158] Analysis of the nutritional quality of rice under different treatments: The quality of rice under the treatment of phosphogypsum land reclamation is shown in Table 17. The soil of this land reclamation has a certain promoting effect on the quality of rice. The average values ​​of vitamin C, organic acid, protein and proline of rice under the treatment of phosphogypsum land reclamation were 0.89 mg·100 g -1 , 0.03%, 7.04% and 0.06% with a coefficient of variation of 2.5% to 16.67%. Compared with CK, vitamin C, organic acid and protein in GB were increased by 29.87%, 50% and 13.01% respectively.

[0159] Table 17 Nutritional content of rice treated with phosphogypsum

[0160]

[0161] Analysis of the difference of heavy metal content in rice under different treatments: The contents of Pb, As, Cd, Cr and Hg in various parts of the tested rice under different treatments are as follows: Fig.12 The Pb contents in the roots, aerial parts and grains of GB-treated rice were 0.650, 1.650 and 0.290 mg kg -1 ; As contents were 0.637, 1.420, and 0.202 mg·kg -1 ; Cd contents were 0.212, 0.140, and 0.033 mg·kg -1 ; Cr contents are 3.470, 5.650, and 2.220 mg·kg -1 ; Hg content range is 0.014, 0.034, 0.005 mg kg -1 The Pb contents in the root, aboveground part and grain of CK rice were 24.00, 1.68 and 0.52 mg·kg, respectively. -1 ; As contents were 11.70, 0.936, and 0.204 mg·kg -1 ; Cd contents were 0.393, 0.184, and 0.049 mg·kg -1 ; Cr contents are 25.40, 5.43, and 3.43 mg·kg -1 ; Hg contents were 0.061, 0.023, and 0.006 mg·kg -1 .

[0162] Since soil heavy metal pollution can accumulate step by step through the food chain and eventually harm human health, this study was evaluated based on the national food safety standards and feed hygiene standards. The corresponding results are shown in Table 12. In all treatments of this experiment, the contents of As, Cd and Hg in rice grains met the limit standards in food in the National Food Safety Standard Limits of Contaminants in Food (GB2762-2022), and the maximum content level allowed in grains (Cd ≤ 0.1 mg kg -1 、As≤0.5mg·kg -1 and Hg≤0.02mg·kg -1 ), the Pb and Cr contents exceeded the limit standard of GB2762-2022 (Pb≤0.2mg·kg -1 and Cr≤1.0mg·kg -1 ), the Pb content in GB and CK treatments exceeded the national standard limit by 2.6 and 1.5 times, respectively, and the Cr content exceeded by 3.4 and 2.2 times, respectively, showing that CK < GB. The Pb, Cd, As and Hg contents in the aboveground parts of rice in all treatments met the requirements of the Feed Hygiene Standard (GB13078-2017) (Pb ≤ 30.0 mg kg -1 、As≤4.0mg·kg -1 、Cd≤1.0mg·kg -1 and Hg≤0.1mg·kg -1 The Cr content in the aboveground part of all treated rice exceeded the requirements of GB13078-2017 (Cr≤5.0mg·kg -1 ), among which, the Cr content in GB treatment of phosphogypsum is lower than that in CK.

[0163] Correlation between the edible part of rice grains and the heavy metal content in soil: There is a certain correlation between the heavy metal content in rice grains and the heavy metal content in soil, such as Fig.13 As shown (Note: *P≤0.05, **P≤0.01). In general, Pb, Cd and Cr in crops are most affected by the heavy metal content in the soil. In the study area, the Pb content in rice grains was extremely significantly positively correlated with soil Pb, and was significantly positively correlated with Hg (R2=0.87 and 0.99), and was extremely significantly negatively correlated with Cr and As (R2=-0.96 and -0.99); the Cd content in rice grains was extremely significantly positively correlated with soil Pb, and was significantly positively correlated with Hg content, with correlation coefficients of 0.97 and 0.82, respectively, and was extremely significantly negatively correlated with Cr and As; the Cr content in rice grains was extremely significantly positively correlated with soil Pb, and was significantly positively correlated with Hg, with correlation coefficients of 1 and 0.91, respectively, and was extremely significantly negatively correlated with Cr and As. There was no obvious correlation between As and Hg in rice grains and the five heavy metals in the soil.

[0164] Difference analysis of heavy metal enrichment factor (BCF) of rice under different treatments: The enrichment factor of each part of the tested rice under different treatments is as follows: Fig.14 The enrichment coefficients of Pb in the root, aboveground part and grain of the tested rice in CK treatment were 0.012, 0.031 and 0.006, respectively; the enrichment coefficients of As were 0.012, 0.026 and 0.004, respectively; the enrichment coefficients of Cd were 0.922, 0.609 and 0.143, respectively; the enrichment coefficients of Cr were 0.035, 0.057 and 0.022, respectively; the enrichment coefficients of Hg were 0.015, 0.037 and 0.005, respectively. The enrichment coefficients of Pb in the root, aboveground part and grain of GB treated rice were 0.258, 0.018 and 0.006, respectively; the enrichment coefficients of As were 0.295, 0.024 and 0.005, respectively; the enrichment coefficients of Cd were 1.709, 0.800 and 0.213, respectively; the enrichment coefficients of Cr were 0.285, 0.061 and 0.038, respectively; the enrichment coefficients of Hg were 0.053, 0.020 and 0.005, respectively. The enrichment capacity of Pb, As, Cd, Cr and Hg in each part showed that the grain < aboveground part < root, and the BCF of aboveground part and grain in each treatment was <1, indicating that the enrichment capacity of rice for heavy metals was weak.

[0165] Analysis of the difference of heavy metal transport coefficient (TF) of rice under different treatments: The enrichment coefficients of each part of the tested rice under different treatments are as follows: Fig.15 As shown. In the CK treatment, the TF root-shoot and TF root-tube of Pb in the tested rice were 2.551 and 0.176, respectively; the TF root-shoot and TF root-tube of As were 2.229 and 0.142, respectively; the TF root-shoot and TF root-tube of Cd were 0.660 and 0.236, respectively; the TF root-shoot and TF root-tube of Cr were 1.629 and 0.393, respectively; the TF root-shoot and TF root-tube of Hg were 2.509 and 0.146, respectively; In GB treatment, the TF root-shoot and TF root-tube of Pb in rice were 0.070 and 0.310, the TF root-shoot and TF root-tube of As were 0.080 and 0.218, the TF root-shoot and TF root-tube of Cd were 0.468 and 0.267, the TF root-shoot and TF root-tube of Cr were 0.214 and 0.632, and the TF root-shoot and TF root-tube of Hg were 0.379 and 0.265. The transport capacity of Pb, As, Cd, Cr and Hg in each part showed that root-shoot <shoot-grain, and the TF of shoot-grain in each treatment was <1, and the transport capacity of rice grain for heavy metals was weak.

[0166] Effect of Buckwheat Planting on Land Reclamation Soil:

[0167] Analysis of Buckwheat Yield and Biological Traits under Different Treatments: The effects of different land reclamation treatments on the growth traits of buckwheat are shown in Table 18. There are significant differences in plant height, stem diameter, biomass, 1000-grain weight, and yield of the tested buckwheat under different treatments. The average yield of buckwheat under different treatments is 854.87 kg·hm -2 , with a coefficient of variation of 14.83%. The yield of each treatment is higher than that of CK. Among them, GA and GB1 reach a significant level, increasing by 130.63% and 95.69% respectively compared with CK, while the improvement effects of GB2 and GB3 compared with CK are not significant, increasing by 0.71% and 12.09% respectively, showing CK < GB2 < GB3 < GB1 < GA; the average values of plant height, stem diameter, biomass, and 1000-grain weight of buckwheat under different treatments are 21.48 cm, 55.88 mm, 7.90 g, and 22.40 g respectively, with a coefficient of variation of 5.88% - 22.40%. Compared with CK, the plant height, stem diameter, biomass, and 1000-grain weight of each land reclamation treatment are significantly increased (P < 0.05), and the improvement effects of GA and GB1 are the best.

[0168] Table 18 Buckwheat Yield and Biological Traits under Different Treatments

[0169]

[0170] Analysis of Buckwheat Nutritional Quality Content under Different Treatments: The effects of different land reclamation treatments on the nutritional quality of buckwheat are shown in Table 19. The change in the total soluble sugar content of buckwheat under the 4 land reclamation treatments is 8.60 - 15.83 mg·g -1 , compared with CK, the GA treatment has the best effect on increasing the total soluble sugar content of buckwheat, and the total soluble sugar content is 16.83 mg·g -1 , which is significantly increased by 84.06% compared with CK, and there is no significant change in other treatments; the change in the soluble protein content of buckwheat under all land reclamation treatments is 2.12 - 4.30 mg·g -1 , compared with CK, the GA treatment has the best effect on increasing the soluble protein content of buckwheat, and the soluble protein content is 4.3 mg·g -1 , which is significantly increased by 6.15% compared with CK, and there is no significant change in other treatments; the change in the protein content of buckwheat under all land reclamation treatments is 6.29% - 14.10%. Compared with CK, the GA and GB1 treatments both increase the protein content of buckwheat. Among them, the GB1 treatment has the best improvement effect, and the content reaches 14.10%, which is significantly increased by 5.55% compared with CK, reaching a significant level. On the contrary, the GB3 treatment significantly reduces the protein content of buckwheat; the change in the proline content of buckwheat under all land reclamation treatments is 0.01% - 0.04%. Among them, the GB3 treatment has the best effect on increasing the proline content of potato, which is significantly increased by 0.03% compared with CK; there is no significant change in the vitamin C content of buckwheat under all land reclamation treatments.

[0171] Table 19 Nutrient content of buckwheat in different treatments

[0172]

[0173] Analysis of the difference of heavy metal content in buckwheat under different treatments: Fig.15 As shown in the figure, the contents of Pb, As, Cd, Cr and Hg in various parts of buckwheat under different treatments were significantly different (P<0.05). The Pb content in the root, stem, leaf and grain of buckwheat under different treatments ranged from 1.52 to 3.92, 0.687 to 1.160, 1.17 to 2.58 and 0.30 to 1.45 mg·kg, respectively. -1 The average values ​​were 2.768, 0.869, 1.840, and 0.658 mg·kg -1 The coefficient of variation was between 1.84% and 5.06%; the As content ranges were 0.036-0.055, 0.019-0.023, 0.039-0.059, and 0.010-0.015 mg·kg -1 The average values ​​were 0.045, 0.020, 0.045, and 0.012 mg·kg -1 , the coefficient of variation was between 5.00% and 8.33%; the Cd content ranges were 0.178-0.441, 0.126-0.436, 0.266-0.873, and 0.039-0.117 mg·kg -1 The average values ​​were 0.254, 0.217, 0.434, and 0.056 mg·kg -1 , the coefficient of variation was between 2.30% and 5.36%; the Cr content ranges were 1.28-3.24, 0.473-0.873, 1.01-1.75, and 0.35-0.49 mg·kg -1 The average values ​​were 2.076, 0.641, 1.366, and 0.420 mg·kg -1 The coefficient of variation was between 1.10% and 3.81%; the Hg content ranges were 0.014-0.023, 0.016-0.019, 0.022-0.029, and 0.015-0.018 mg·kg -1 The average values ​​were 0.019, 0.018, 0.026 and 0.016 mg kg -1 , the coefficient of variation is between 3.85% and 6.25%.

[0174] Since soil heavy metal pollution can accumulate through the food chain and eventually harm human health, this study is based on the national food safety standards and feed hygiene standards. The corresponding results are as follows Fig.16 In all treatments of this experiment, the contents of Cd, Cr, As and Hg in buckwheat grains met the limit standards in food in the National Food Safety Standard Limits of Contaminants in Food (GB2762-2022), and the maximum content level allowed in grains (Cd ≤ 0.1 mg kg -1 、Cr≤1.0mg·kg -1 、As≤0.5mg·kg -1 and Hg≤0.02mg·kg -1 The Pb content of buckwheat grains exceeds the limit set in GB2762-2022 (Pb ≤ 0.2 mg kg -1 ), GA, GB1, GB2, GB3 and CK exceeded the national standard limit by 2.85, 7.25, 1.5, 2.5 and 2.35 times, respectively, showing GB2<CK<GB3<GA<GB1. The contents of Pb, Cd, As, Cr and Hg in the roots, stems, leaves and grains of all treatments of buckwheat met the requirements of the Feed Hygiene Standard (GB13078-2017) (Pb≤30.0mg·kg -1 、As≤4.0mg·kg -1 、Cd≤1.0mg·kg -1 、Cr≤5.0mg·kg -1 and Hg≤0.1mg·kg -1 ).

[0175] Correlation between the edible part of buckwheat seeds and the heavy metal content in the soil: There is a certain correlation between the heavy metal content in buckwheat seeds and the heavy metal content in the soil, such as Fig.17 As shown (Note: *P≤0.05, **P≤0.01). In general, Pb, Cd and Cr in crops are most affected by the content of heavy metals in the soil. In the study area, Pb in buckwheat grains was extremely significantly positively correlated with soil Pb and Hg, and significantly positively correlated with Cd and As (R2=0.0.76, 0.85, 0.61 and 0.55); Cd content in buckwheat grains was extremely significantly positively correlated with soil Cr and As, and significantly positively correlated with Cd content, with correlation coefficients of 0.94, 0.71 and 0.63, respectively, and extremely significantly negatively correlated with Pb; Cr content in buckwheat grains was extremely significantly positively correlated with soil As, and significantly positively correlated with Cd and Cr, with correlation coefficients of 0.76, 0.62 and 0.63, respectively. There was no obvious correlation between As and Hg in buckwheat grains and the five heavy metals in the soil.

[0176] Analysis of the difference of heavy metal enrichment factor (BCF) of buckwheat under different treatments: Fig.18As shown in the figure, there were significant differences in the enrichment coefficients of each part of the tested buckwheat under different treatments (P<0.05). The enrichment coefficients (3-15a) of Pb in the roots, stems, leaves, and grains of the tested buckwheat under different treatments ranged from 0.035 to 0.070, 0.01 to 0.03, 0.021 to 0.052, and 0.005 to 0.021, respectively, with average values ​​of 0.051, 0.017, 0.035, and 0.012, respectively, and the coefficient of variation was 2.26% to 4.77%; the enrichment coefficients (3-15b) of As ranged from 0. The enrichment coefficients of Cd (3-15c) were 0.861-2.069, 0.748-1.897, 1.335-3.796, 0.204-0.069, 0.764-1.897, 1.335-3.796, 0.204-0.012, with average values ​​of 0.020, 0.008, 0.018, and 0.005, respectively, and the coefficients of variation were 1.51%-2.63%. The enrichment coefficients of Cr (3-15d) ranged from 0.016 to 0.171, 0.011 to 0.029, 0.022 to 0.053, and 0.006 to 0.022, with average values ​​of 0.082, 0.021, 0.046, and 0.015, respectively, and the coefficient of variation was 4.59% to 12.33%. The enrichment coefficients of Hg (3-15e) ranged from 0.016 to 0.021, 0.013 to 0.021, 0.019 to 0.033, and 0.012 to 0.019, with average values ​​of 0.019, 0.018, 0.026, and 0.016, respectively, and the coefficient of variation was 4.43% to 9.29%. The heavy metal enrichment capacity of each part was grain < stem < root < leaf. The BCF of the grains of the edible parts of buckwheat in each treatment was <1, and the enrichment capacity of buckwheat grains for heavy metals was weak.

[0177] Analysis of the difference of heavy metal transport coefficient (TF) of buckwheat under different treatments: Fig.19As shown in the figure, there were significant differences in the transport coefficients among the various parts of the tested buckwheat under different treatments (P<0.05). The TF root-stem, TF stem-leaf, and TF stem-grain (3-16a) of Pb in the tested buckwheat under different treatments ranged from 0.274 to 0.452, 1.707 to 2.404, and 0.432 to 1.426, respectively, with average values ​​of 0.329, 2.112, and 0.743, respectively, and the coefficient of variation was 5.46% to 6.34%; the TF root-stem, TF stem-leaf, and TF stem-grain (3-16a) of As in the tested buckwheat under different treatments ranged from 0.274 to 0.452, 1.707 to 2.404, and 0.432 to 1.426, respectively, with average values ​​of 0.329, 2.112, and 0.743, respectively, and the coefficient of variation was 5.46% to 6.34%. The ranges of TF root-stem, TF stem-leaf, and TF stem-seed (3-16a) of Cd were 0.340-0.557, 1.946-2.619, and 0.536-0.664, with average values ​​of 0.457, 2.249, and 0.612, respectively, and the coefficients of variation were 6.51%-15.72%. The ranges of TF root-stem, TF stem-leaf, and TF stem-seed (3-16a) of Cd were 0.566-1.065, 1. 785~2.410, 0.192~0.310, with average values ​​of 0.839, 2.022, and 0.261, respectively, with coefficients of variation of 2.40%~6.78%; the ranges of TF root-stem, TF stem-leaf, and TF stem-grain (3-16a) of Cr were 0.146~0.683, 2.005~2.273, and 0.562~0.740, with average values ​​of 0.35 6, 2.151, 0.673, and the coefficient of variation was 3.47%-4.66%; the TF root-stem, TF stem-leaf, and TF stem-grain (3-16e) of Hg ranged from 0.715 to 1.295, 1.269 to 1.618, and 0.863 to 0.947, respectively, with average values ​​of 0.947, 1.487, and 0.907, respectively, and the coefficient of variation was 3.31%-11.22%. In this study, the transport coefficients of As, Cd, Cr, and Hg in various parts of buckwheat were all root-stem < stem-grain < stem-leaf. Except for the stem-leaf part, which was greater than 1, the transport coefficients of As, Cd, Cr, and Hg in the tested buckwheat parts were all less than 1.

[0178] Effect of soil modification using solid waste on crop yields:

[0179] Crop growth and development indicators and yield are important indicators for testing soil nutrients and quality. This study found that modified phosphogypsum soil can significantly improve the biological traits of corn, rice, potato and buckwheat, such as plant height, stem thickness, biomass, etc., thereby increasing crop yield. In the process of planting fruit trees, sweet clover and corn, after applying phosphogypsum, it was found that the content of trace elements in the soil increased, and the crop yield also increased. The results of the study are consistent. Phosphogypsum contains a large amount of Ca and S elements and a small amount of P, F, Si, Fe and other nutrients necessary for plant growth, which can improve soil fertility and serve as a good nutrient source for crops, thereby promoting crop growth and development. The use of phosphogypsum for application on crops such as rice, corn, soybeans, vegetables and fruit trees is consistent with the results of the study. Experiments were conducted to study its effects on crop growth and development. It was found that rice turned green 2 to 3 days earlier, tillering was also advanced accordingly, the number of effective ears increased by 300,000 to 450,000 ears per hectare, and the 1000-grain weight increased by 0.30 to 0.80 g. At the same time, the empty stalk rate of corn was relatively reduced by 0.08% to 0.11%, the 100-grain weight increased by 0.40 to 1.30 g, the soybean pod setting rate increased by about 5%, and the crop yield increased by 5.20% to 19.90%, which is consistent with the results of this study. Under the phosphogypsum land reclamation treatment in this study, the yields of corn, potato, rice and buckwheat increased by 0.71% to 130.63% compared with the control, respectively, which is consistent with the existing results. The use of phosphogypsum in agricultural production has a significant promoting effect on crop growth and yield. When phosphogypsum was applied as a soil conditioner, it was found that corn biomass increased with the increase of phosphogypsum addition level, which was slightly different from the buckwheat planting results in this study. This was because phosphogypsum was used for land reclamation in this study, and the amount of phosphogypsum used was relatively large compared with previous studies using it as a soil conditioner. In the buckwheat planting experiment of this study, the treatment with a smaller amount of phosphogypsum added had a better yield increase effect under the three phosphogypsum land reclamation ratios. Therefore, when using phosphogypsum for land reclamation, attention should be paid to using the appropriate ratio.

[0180] Phosphate tailings contain a large amount of P, Mg, Ca and other elements, which are essential nutrients for plants in their growth process. Many studies have shown that calcium magnesium phosphate fertilizer can be prepared using phosphorus tailings as raw materials, which is a good fertilizer source, so it is often used in agriculture. The organic fertilizer prepared by mixing phosphorus tailings with straw and soy sauce residue through microbial fermentation can significantly improve the physical and chemical properties of the soil; adding a certain proportion of phosphorus tailings powder to prepare a phosphorus-containing agricultural water-retaining agent, which has excellent water absorption and water retention properties, and can also release phosphorus for crop growth; using phosphorus tailings, bentonite and other mineral resources, a phosphorus-supplying soil conditioner is prepared, which can significantly improve the physical and chemical properties of acidic soils; existing research mainly focuses on calcium magnesium phosphate fertilizers, soil improvers, water-retaining agents, etc., which is different from the modification of phosphorus tailings for artificial land reclamation in this study, but previous studies have successfully used phosphorus tailings as a crop fertilizer source, indicating that phosphorus tailings have a certain feasibility as land reclamation and conversion. The yield of crops after restoration of cultivation was equal to that of other cultivated land in the area 4 to 5 years after restoration of cultivation, with good economic benefits. In this study, the biological traits and yield of corn planted in the phosphate tailings land reclamation treatment, such as plant height, stem diameter and 100-grain weight, were lower than those of the control, and the yield decreased by 5.84% to 6.47% compared with the control. The reason for this may be that the corn planted in this study was the first crop planted after land reclamation, and the beneficial nutrients in the phosphate tailings have not been fully utilized, which requires further study. However, the yield of corn planted in the phosphate tailings land reclamation treatment in this study was still within the average per-acre yield of fresh glutinous corn in Yunnan Province (500 to 700 kg), indicating that phosphate tailings land reclamation still has good application prospects.

[0181] Effects of soil modification using solid waste on crop nutritional quality:

[0182] Nutritional quality indicators include vitamin content, protein content and sugar content. Nutritional quality indicators are important indicators for measuring the edible value of agricultural products, which are conducive to the selection of crop varieties and quality evaluation. Cereals and tuber crops such as corn, rice, potatoes and buckwheat are rich in nutrients and are high-quality food. The results show that the quality and quality of wheat grown in soils with phosphogypsum are improved compared with the control without addition. The sugar beet planting experiment using improved materials such as phosphogypsum found that the soluble sugar content and proline content of the leaves increased by 27.58% and 72.97% during the expansion period of sugar beet tubers. The study found that the use of some technologies to transform phosphogypsum can produce highly water-soluble nitric phosphate fertilizers with a water solubility of ≥99.9%, which has a high utilization rate and meets the needs of some economic crops, increasing crop yields while also improving the quality of agricultural products. The results of this experimental study show that under the treatment of modified phosphogypsum, the soluble sugar content, protein content and vitamin C content of corn, rice and buckwheat are significantly higher than those of the control, and the protein content in potato tubers is also significantly higher than that of the control. Among them, the stratified treatment has a better improvement effect, which is consistent with the results of previous studies. Other studies have found that the silicon element contained in phosphorus chemical solid waste can stimulate sugar metabolism and has a biological activation effect on the growth of many crops. Phosphogypsum and phosphorus tailings resources have a certain impact on the nutritional quality of crops. This is because the high content of nutrients in phosphogypsum and phosphorus tailings can be used as fertilizer to replenish the soil, thereby promoting crop growth and development and improving nutritional quality.

[0183] Regarding the safety of agricultural products from soil modified from solid waste:

[0184] Phosphogypsum and phosphate tailings contain harmful impurities such as heavy metals. These impurities will accumulate in the soil during land reclamation, affecting soil quality. They can also be absorbed by plants and enriched in agricultural products. They accumulate step by step through the food chain and pose a potential threat to human health. Therefore, it is of great significance to conduct safety evaluation of soil and harvested agricultural products. By comparing the application of phosphogypsum in various places, it was found that the Cd accumulated in grains was within the allowable range, and the heavy metal content in crop grains was lower than the national feed control standard. Studies have shown that the use of phosphogypsum in agricultural production in coastal saline-alkali land is safe and effective, but experiments on alkaline soils have caused people to worry about the safe use of phosphogypsum. The study found that increasing the use of phosphogypsum will increase the heavy metal pollution level of soybean grains and stems, and the heavy metal enrichment capacity of soybean stems is higher than that of soybean grains. The mineral structure, elemental composition and heavy metal content of phosphogypsum were measured and studied. The results showed that phosphate tailings are risk-free when used in agricultural production, and can improve soil structure and environment, and increase the nutrients required for plant growth. The contents of five heavy metals in the kernels of the edible parts of corn planted in this study all reached the safe consumption standards, but the contents of Pb and Cd in potato tubers, the contents of Pb and Cr in rice kernels, and the contents of Cr in the aboveground stems and leaves did not meet the national limit requirements. This study also found that the heavy metal contents of crops in some treatments were lower than those in the control soil, which is different from the results of previous studies. The reason for this may be that the heavy metal background value of the land reclamation soil resources used in this study was relatively high, resulting in an increase in the accumulation of heavy metals in crops.

[0185] The agricultural use of phosphogypsum may cause pollutants to migrate, accumulate and transform through the soil-crop system, thereby endangering the ecosystem and human health; the study observed that different crops or different parts of the same crop have different enrichment abilities for heavy metals, and found that crop straw has a stronger ability to enrich heavy metals than grains. In this study, there were certain differences in the accumulation of heavy metals in corn, rice, buckwheat and potatoes, and it was found that the enrichment and transportation abilities of non-edible parts for heavy metals were stronger than those of edible parts, grains and tubers, which is consistent with the results of previous studies. Therefore, whether the enrichment and transportation abilities of non-edible parts of other crops are stronger than those of edible parts, and whether food safety can be guaranteed, requires further study. In this study, corn planted in the phosphogypsum-reclaimed soil at the test site was safe and effective, but potatoes and rice planted at the Dongchuan test site did not meet safety standards. The reason for this may also be that the source of phosphogypsum is different from the process of producing phosphate fertilizers, and the heavy metal content in phosphogypsum is different. Campbell et al. used phosphogypsum in acidic soils and found that the mobility of heavy metals in soil decreased with the increase of phosphogypsum usage, and phosphogypsum can significantly reduce the leaching of heavy metals in soil. This is consistent with the results of this study, which found that the heavy metal content in buckwheat seeds tended to decrease with the increase of phosphogypsum ratio. Therefore, follow-up testing and strict control must be carried out during agricultural use to ensure soil cleanliness and the safety and health of agricultural products.

[0186] There is a certain correlation between the heavy metal content in crops and the heavy metal content in soil. Taking farmland soil-corn crops as the research object, the correlation analysis between heavy metal pollution in cultivated soil and heavy metals in crops shows that some heavy metal elements in corn grains have a certain correlation with heavy metal elements in soil; the content of heavy metal elements in major crops and soil was analyzed, and it was found that there was a positive correlation and a negative correlation between heavy metals in rice, pepper and betel nut fresh fruits, and there was an obvious synergistic absorption between heavy metals. Heavy metals in agricultural products mainly come from soil absorption. The results of this study are consistent with the results of previous studies. The heavy metal content in the edible parts of corn, rice, potato and buckwheat planted in this study has a certain correlation with the heavy metals in the soil, and the correlation of different crops is different, and the research results are also consistent. This study found that the difficulty and metabolic mode of crops absorbing heavy metal elements in the soil vary depending on the type of crops, and the correlation between the heavy metal content in different crops and the content in the soil is different. Due to the difference in water conditions, the absorption of heavy metal elements by crops in dry fields and paddy fields shows obvious differences.

[0187] The above shows and describes the basic principles and main features of the present invention and the advantages of the present invention. It should be understood by those skilled in the art that the present invention is not limited to the above embodiments. The above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention to be protected. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A method for detecting the impact of soil modified by phosphorus chemical solid waste on crops, characterized in that: The following steps are involved: Step 1: Select the experimental raw materials: The raw materials mainly include phosphogypsum, phosphorus tailings and arable soil from local unused land. The phosphogypsum raw materials used for land reclamation are washed 2 to 3 times by the factory's water washing equipment before leaving the factory to reduce the concentration of harmful elements. The washed phosphogypsum is then modified by adding about 0.4% to 0.6% of a modifying agent to adjust the pH value of the phosphogypsum and fix the fluoride content in the phosphogypsum. After fully mixing, the mixture is piled up for 3 to 5 days for full reaction to obtain the modified phosphogypsum. The experiment used two land reclamation processes, namely layered reconstruction process A and integrated land reclamation process B; Step 2: Regional test design, including the following: test area S21, test area S22 and test area S23; Step 3: Sample collection and analysis test, including the following: S31: Sample collection and preparation; S32: Crop yield statistical method; S33: Crop heavy metal content and quality determination method; Step 4: Data processing and statistics: Excel 2021 and SPSS25 software were used to perform statistical analysis on the data, and Origin 2021 software was used to draw charts. The data obtained from the experiment were averaged three times, and the comparison of the averages was performed using the least significant difference method; Step 5: Results and analysis: The soil artificially reclaimed from phosphorus chemical solid waste can generally meet the requirements of normal growth and development of crops such as corn, potato, buckwheat, and rice. Comprehensively considering the impact of phosphogypsum artificial soil on crop growth, it is believed that process A is better than process B between the two processes; combined with the content of five heavy metals in crops, it is found that the heavy metal content of corn planted using phosphogypsum and phosphate tailings reclaimed soil meets the standards and can be applied to agricultural production. Rice planted in paddy fields reclaimed from phosphogypsum and potatoes and buckwheat planted in dry land first need to ensure that the heavy metal content of the local imported soil meets the standards, otherwise it will affect the safety of the food chain. This also shows that the utilization of modified phosphogypsum for land reclamation is feasible under the premise of ensuring the quality of the imported soil.

2. The method for detecting the impact of soil modified by phosphorus chemical solid waste on crops according to claim 1, characterized in that: The test area S21 is divided into the following steps: S211. Overview of the test site: The test site is located at 24°81′N, 102°37′E, 2215m above sea level, with an average annual temperature of 14.7℃ and an average annual precipitation of 876.48mm. S212. Test materials: Two types of solid waste from the phosphorus chemical industry and soil were selected as raw materials. The solid waste raw materials were phosphogypsum and phosphorus tailings. The guest soil was the zonal arable layer soil (0-20 cm) distributed in the unused land near the test site. The test crop was fresh glutinous corn, and the corn variety was the main local variety. S213, Experimental design: The experimental area is about 1000m 2 Two land reclamation processes, A and B, were used. The pollutant content of each land reclamation process was in line with GB15618-2018, and the background value of heavy metal elements in the control soil was normal; there were five treatments in total, each with 160m 2 , 1.5m interval zones were set between different treatments; For corn planting, double-row planting is adopted according to local planting habits, with a row spacing of 45cm×55cm. Before corn sowing, 800kg / mu of ecological organic fertilizer is spread to fertilize the soil. During the growth period of the crop, irrigation, weeding and pest control are carried out according to normal field operation methods. During the tasseling stage of corn, 50kg / mu of urea is applied.

3. The method for detecting the impact of soil modified by phosphorus chemical solid waste on crops according to claim 1, characterized in that: The test area S22 is divided into the following steps: S221. Overview of the test site: The test site is located at 26°13′N, 103°8′E, 1583.8m above sea level, with an average annual temperature of 20.5℃ and an annual precipitation of 650mm, which is suitable for growing crops such as corn and rice. S222. Test materials: Phosphogypsum and soil were used as raw materials. The soil was zonal arable soil from unused land near the test site. The test crops were rice and potatoes, both of which were the main local varieties. S223. Experimental design: The experimental dry land used two land reclamation processes, A and B, and the paddy field used process B. There were three treatments in the dry land, and potatoes were planted in double rows according to local planting habits, with a row spacing of 35cm×60cm; there were two treatments in the paddy field, and rice was planted with a row spacing of 25cm×25cm. The pollutant content of each land reclamation treatment was in compliance with GB15618-2018, and the background value of heavy metal elements in the control soil was normal; Before sowing rice, spread 300kg / mu and 50kg / mu of biological organic fertilizer and ternary compound fertilizer N:P2O5:K2O=15:15:15 to fertilize the soil. Before sowing potatoes, spread 80kg / mu of ternary compound fertilizer N:P2O5:K2O=16:7:12 to fertilize the soil. During the growth period of crops, irrigation, weeding and pest control are carried out according to routine field operations.

4. The method for detecting the impact of soil modified by phosphorus chemical solid waste on crops according to claim 1, characterized in that: The test area S23 is divided into the following steps: S231. Test site overview: The test site is located at 26°7′N, 104°7′E, 1989.9m above sea level, with an average annual temperature of 13.4℃ and an annual precipitation of 935mm. S232. Test materials: Phosphogypsum and soil were used as raw materials. The soil was the zonal arable soil distributed locally near the test site. Buckwheat was the main crop variety grown locally. S233, Experimental design: The experimental area is about 800m 2 , using two land reclamation processes, A and B, with a total of five treatments, each with 120m 2 , a 1.5m interval zone was set between different treatments, and the pollutant content of each land reclamation treatment was in line with GB15618-2018, and the background value of heavy metal elements in the control soil was normal; Before sowing buckwheat, spread 300 kg of biological organic fertilizer and 50 kg of triple compound fertilizer N: P2O5: K2O = 15:15:15 per mu to fertilize the soil. During the growth period of the crop, irrigation, weeding and pest control should be carried out according to routine field operations.

5. The method for detecting the impact of soil modified by phosphorus chemical solid waste on crops according to claim 1, characterized in that: S31: Sample collection and preparation: Plant samples were collected using the five-point sampling method, and representative plants were selected. Five whole plants of corn, rice and potato plants were collected from each plot, and buckwheat plants were collected at 1m 2 Five points were collected in each plot of the sample area, and the growth indicators such as plant height of the selected plants were measured respectively, and the number of plants was counted. After being brought back to the laboratory, the plant samples were divided into multiple parts according to their nutritional organs. Metal utensils were avoided in the preparation process. They were first rinsed with pure water and then washed with deionized water. After air-drying, they were weighed and the fresh weight was recorded. Then, large pieces of plant samples were cut into small pieces with a quartz knife and put into a mesh bag. A part of the fresh samples was kept for determining quality indicators, and the remaining samples were fixed in an oven at 105°C for 30 minutes, then adjusted to 65°C for drying until the mass was constant. After determining the dry mass, they were crushed with a grinder and passed through a 100-mesh nylon mesh sieve and bagged for testing.

6. The method for detecting the impact of soil modified by phosphorus chemical solid waste on crops according to claim 1, characterized in that: The S32: crop yield statistical method: before collecting plant samples, various growth indicators of various crops are measured, and the plant height, leaf length, leaf width, etc. are measured with a tape measure, the stem diameter is measured with a vernier caliper, and the fresh weight is measured with an electronic balance; then the whole plant sample is collected and put into a mesh bag and immediately taken back to the laboratory, the potato tuber fresh weight is weighed to calculate the theoretical per-acre yield of each plot, corn, rice and buckwheat are threshed, dried, and the dry weight is weighed, and finally the theoretical per-acre yield of each plot is calculated for analyzing the crop yield increase effect.

7. The method for detecting the impact of soil modified by phosphorus chemical solid waste on crops according to claim 1, characterized in that: The fourth step comprises: Enrichment factor: Bioaccumulation coefficient is an important indicator of heavy metal accumulation in crops. It is used to evaluate the ability of various parts of crops to accumulate heavy metals. The larger the BCF, the stronger its ability to accumulate heavy metals. When BCF is greater than 1, it indicates that crops have a strong ability to accumulate heavy metals. The calculation formula is: In the formula, BCFi is the enrichment coefficient of each heavy metal element in the i part of the test crop, Ci is the heavy metal content in the i part of the test crop, and Cs is the heavy metal content in the corresponding rhizosphere soil; Transport coefficient: The transport coefficient indicates the ability of heavy metal transport and distribution between various parts of crops. The larger the TF, the stronger its ability to transport heavy metals. The calculation formula is: Where TF 下部位-上部位 TF and C are the heavy metal contents in each nutritional part of the test crops from the lower part to the upper part, respectively.

Images