A soil conditioner for passivating cadmium and mercury compound pollution and improving the nutritional quality of rice and its application

Abstract

The present invention relates to the technical field of rice planting, and discloses a soil conditioner for passivating cadmium-mercury combined pollution and improving the nutritional quality of rice, and its application. The soil conditioner comprises the following components: a pH regulator, sepiolite, phosphate, sulfate, an iron-based antagonist, and a zinc-based antagonist. The soil conditioner of the present invention can effectively passivate the cadmium-mercury combined pollution in the soil, reduce the absorption of cadmium and mercury by rice, and at the same time improve the nutritional quality of rice, and the effect is stable, and it can be widely applied in large fields.

Description

Technical Field

[0001] The present invention relates to the technical field of rice cultivation, and particularly relates to a soil conditioner for passivating cadmium-mercury combined pollution and improving the nutritional quality of rice, and its application. Background Art

[0002] With the rapid development of industrialization and urbanization in China, the phenomenon of soil heavy metal pollution has gradually emerged. The over-standard rate of various pollutants in cultivated land soil in China is as high as 19.4%, and the main pollutants are cadmium (Cd), mercury (Hg), arsenic (As), copper (Cu) and lead (Pb). Taking Cd as an example, 1.46 million tons of crops with excessive Cd content are produced every year, and the situation is not optimistic. Soil heavy metal pollution has the characteristics of non-degradability and long duration. How to effectively repair and manage soil heavy metals and utilize them safely is a hot spot and a difficult point nowadays.

[0003] At present, the repair and management of soil heavy metals are mainly based on two mechanisms. One is to remove heavy metals in the soil from the source through technologies such as phytoremediation and soil washing, and the other is to reduce the availability of heavy metals in the soil by stabilizing or solidifying heavy metals. Although the former can completely eliminate heavy metals in the soil from the source, these methods all have problems such as long time consumption, low repair efficiency, and high cost, and are not suitable for large-scale application.

[0004] Most soil conditioners are made mainly of natural minerals, and have a significant effect on improving the physical and chemical properties of the soil, changing the soil structure and repairing soil pollution, and have the advantages of high efficiency, low cost and environmental friendliness. At present, there are many studies on soil conditioners for single pollution. For example, biochar, potassium feldspar, sepiolite, phosphate rock powder and lime all have good passivation effects on Cd in the soil. However, farmland soil is often polluted by multiple heavy metals in combination, and combined pollution is more harmful to the soil environment than single pollution, and the repair difficulty is also higher. Cadmium (Cd) and mercury (Hg) are two common toxic elements in the soil, and their combined pollution often occurs in farmland. However, there are few studies on passivators for cadmium-mercury combined pollution, and there are also few studies on promoting plant growth and increasing the absorption and transport of heavy metals by plants.

[0005] There are only two patents related to this, namely, a soil conditioner for repairing cadmium-mercury combined pollution and its application method (CN109810711A) and a conditioner for passivating cadmium and mercury combined polluted farmland soil and its preparation method (CN106753383A). However, they mainly discuss the application under simulated soil conditions (pot experiments), and there are problems such as unstable effects and difficulty in large-scale popularization and application. Since the effect of the conditioner on immobilizing heavy metals is affected by the nature of the soil itself and the surrounding environmental conditions, and the environments of field experiments and pot experiments are not exactly the same, and the field environment is more vulnerable to natural and human factors, the field application effect of pot experiments will be greatly reduced (Wang Yanhong et al., 2018). Summary of the Invention

[0006] To solve the technical problems of the existing soil conditioner for passivating cadmium and mercury combined pollution with unstable effects and difficulty in large-scale popularization and application, the present invention provides a soil conditioner for passivating cadmium and mercury combined pollution and improving the nutritional quality of rice and its application. This soil conditioner can ensure the effect of passivating cadmium and mercury combined pollution in the soil, reduce the absorption of cadmium and mercury by rice, improve the nutritional quality of rice, and has stable effects, and can be widely applied in large fields.

[0007] The specific technical solution of the present invention is as follows:

[0008] In the first aspect, the present invention provides a soil conditioner for passivating cadmium and mercury combined pollution and improving the nutritional quality of rice, which comprises the following components: pH regulator, sepiolite, phosphate, sulfate, iron-based antagonist, zinc-based antagonist.

[0009] In the soil conditioner formula of the present invention, the pH regulator can improve the pH environment of the soil; sepiolite can adsorb and fix heavy metal ions in the soil, and at the same time, the Si ions contained in it can hinder the transport of heavy metal ions to the above-ground part through coprecipitation and other ways; phosphate can fix heavy metals; sulfate can also promote the growth and reproduction of sulfate-reducing bacteria, and sulfate-reducing bacteria can reduce SO 4 2- to S 2- and react with Cd and Hg to form CdS and HgS precipitates, thereby reducing the availability of heavy metals in the soil and ultimately reducing the absorption, accumulation and harm of cadmium and mercury by crops; iron-based antagonists and zinc-based antagonists can react with Cd 2+ and Hg 2+Competitive transporters (such as OsIRTs), thus being able to improve the effect of soil conditioners in reducing the absorption of cadmium and mercury by rice while increasing the iron and zinc content in rice, thereby improving the nutritional quality of rice and providing essential trace elements for the human body. Moreover, multiple repeated field trials have shown that the soil conditioner of the present invention can adapt to the field environment. When widely applied on a large scale, it has the effects of stably passivating the combined cadmium and mercury pollution in the soil, reducing the absorption of cadmium and mercury by rice, and improving the nutritional quality of rice, and is suitable for the remediation of polluted soil in large areas of farmland to achieve safe rice production.

[0010] In addition, all kinds of material raw materials used in the present invention are common ordinary substances, with rich resources, low price and easy availability. The preparation method is simple (simple blending is enough), and it can be used alone or applied together with conventional base fertilizers while reducing the amount of base fertilizers, without increasing additional labor, and has broad application prospects.

[0011] Preferably, the pH regulator includes quicklime or controlled-release quicklime microspheres; the controlled-release quicklime microspheres are composed of an amino-functionalized quicklime core layer and a carboxylated polylactic acid shell layer coated outside the amino-functionalized quicklime core layer.

[0012] Quicklime can increase the pH value of acidic soil, promote the hydrolysis of soil heavy metal ions, and enhance the adsorption, complexation or precipitation of soil colloids on heavy metal ions, thereby reducing the availability of heavy metal ions in the soil. In addition, sulfate-reducing bacteria are difficult to grow in soil with pH < 5. Using quicklime to increase the pH value of acidic soil is beneficial to create more suitable conditions for the growth and reproduction of sulfate-reducing bacteria, which is conducive to their conversion of available Cd and Hg into CdS and HgS precipitates that cannot be absorbed by rice after sulfate reduction.

[0013] However, both too low and too high soil pH are not conducive to the growth and development of rice; moreover, since sulfate-reducing bacteria will convert Hg into more toxic methylmercury while converting Cd and Hg into CdS and HgS, it is necessary to control the soil pH within an appropriate range to prevent excessive reproduction of sulfate-reducing bacteria and the generation of a large amount of methylmercury, so as to cooperate with other components in the soil conditioner to achieve a better effect of passivating the combined cadmium and mercury pollution. Therefore, when using quicklime as the pH regulator, in order to control the soil pH within a suitable range, it is necessary to determine the dosage of quicklime in the soil conditioner according to the soil pH value before use, which is inconvenient to use.

[0014] For this reason, the present invention designs controlled-release quicklime microspheres with a specific structure, which can reversibly adjust OH according to the soil pH -Release rate: When the pH is low, the carboxyl groups in carboxylated polylactic acid are protonated, weakening the electrostatic interaction with amino groups. The binding between the core and the shell becomes loose, facilitating the entry of water into the core layer to react with calcium oxide and accelerating the release of OH - ; when the pH is high, the carboxyl groups in carboxylated polylactic acid are deprotonated, strengthening the electrostatic interaction with amino groups. The core and the shell are tightly bound, which can slow down the contact between water and the core layer and the release of OH - . Therefore, compared with quicklime, the controlled-release quicklime microspheres can adapt to a wider range of soil pH values at a fixed addition amount, adjust the soil pH to an appropriate range at the initial stage of applying the soil conditioner, which is beneficial to the rapid passivation of cadmium and mercury combined pollution in the soil, and is beneficial to the growth and development of rice after planting rice. In addition, the polylactic acid-based shell material used in the present invention can be naturally degraded in the soil and has a suitable degradation period, and will not be degraded too quickly to cause sudden release of calcium oxide, resulting in a large increase in soil pH and affecting the growth and development of rice.

[0015] Preferably, the soil conditioner comprises the following components in parts by weight: 10 - 30 parts of quicklime or 10 - 50 parts of controlled-release quicklime microspheres, 10 - 30 parts of sepiolite, 10 - 30 parts of phosphate, 5 - 10 parts of sulfate, 3 - 8 parts of iron-based antagonist, and 2 - 5 parts of zinc-based antagonist.

[0016] Preferably, the phosphate comprises calcium magnesium phosphate fertilizer; the sulfate comprises potassium sulfate; the iron-based antagonist comprises ferric sulfate; and the zinc-based antagonist comprises zinc sulfate.

[0017] Preferably, the preparation method of the controlled-release quicklime microspheres comprises the following steps:

[0018] (1) After making a mixed solution of an amino silane coupling agent and an anhydrous solvent, adding quicklime powder thereto, carrying out a dehydration condensation reaction, separating the product, and obtaining aminoated quicklime;

[0019] (2) Mixing lactide, hydroxycitric acid and a catalyst, and carrying out a polymerization reaction in an anaerobic environment to obtain carboxylated polylactic acid;

[0020] (3) Dissolving the carboxylated polylactic acid and a crosslinking agent in a solvent to make a coating solution, and carrying out spray coating on the aminoated quicklime with the coating solution, followed by curing and crosslinking to obtain the controlled-release quicklime microspheres.

[0021] In step (1), the amino-silane coupling agent hydrolyzes to generate silanol groups, which then undergo a dehydration condensation reaction with the hydroxyl groups on the surface of calcium oxide, enabling the covalent grafting of the amino-silane coupling agent onto the surface of calcium oxide. In step (2), under the action of a catalyst, lactide undergoes ring-opening polymerization to form polylactic acid. Meanwhile, hydroxycitric acid utilizes two of its hydroxyl groups and three carboxyl groups to undergo an esterification reaction with polylactic acid, introducing multiple carboxyl groups onto the side chains of the finally obtained polylactic acid molecular chains. In step (3), after coating the carboxylated polylactic acid onto the surface of amino-functionalized quicklime by spray coating, the carboxylated polylactic acid shell is cured and crosslinked, which can avoid irreversible damage to the shell at a lower pH and make it difficult to restore to a dense coating state after the pH increases, resulting in - excessive release of OH

[0022] Preferably, in step (1), the volume ratio of the amino-functionalized silane coupling agent to the anhydrous solvent is 1:10 - 20.

[0023] Preferably, in step (1), the addition amount of the quicklime powder in the mixed solution is 0.05 - 0.25 g / mL.

[0024] Preferably, in step (1), the temperature of the dehydration condensation reaction is 20 - 30 °C, and the time is 1 - 2 h.

[0025] Preferably, in step (2), the mass ratio of lactide to hydroxycitric acid is 100:15 - 20.

[0026] Preferably, in step (2), the catalyst is zinc lactate; the mass ratio of lactide to the catalyst is 0.4 - 0.8.

[0027] Preferably, in step (2), the temperature of the polymerization reaction is 140 - 160 °C, and the time is 24 - 36 h.

[0028] Preferably, in step (3), the mass ratio of the carboxylated polylactic acid to the solvent is 1:3 - 5.

[0029] Preferably, in step (3), the crosslinking agent is dicumyl peroxide; the mass ratio of the carboxylated polylactic acid to the crosslinking agent is 1:0.001 - 0.003.

[0030] Further, in step (3), the temperature of the curing and crosslinking is 120 - 130 °C, and the time is 20 - 30 min.

[0031] In a second aspect, the present invention provides the application of the soil conditioner in passivating the cadmium and mercury combined pollution in paddy field soil and improving the nutritional quality of rice.

[0032] Preferably, the application includes the following steps:

[0033] S1: After loosening the surface soil, apply the soil conditioner on the soil surface;

[0034] S2: Mix the soil conditioner with the soil thoroughly, and start planting rice after balancing.

[0035] Further, in step S1, the application rate of the soil conditioner on the soil surface is 150 - 450 kg / mu, and more preferably 300 - 350 kg / mu.

[0036] Within a certain range, as the application rate of the soil conditioner increases, its effect of passivating cadmium and mercury combined pollution in the soil and reducing the absorption of cadmium and mercury by rice improves. However, when the application rate is too high, it will affect the physical and chemical properties of the soil, affect the cation exchange capacity, organic matter content of the soil, and the interaction between ions, resulting in a weakened passivation effect on cadmium and mercury combined pollution in the soil and an increase in the absorption and accumulation of cadmium and mercury by rice. Based on this, the application rate of the soil conditioner in the present invention is controlled at 150 - 450 kg / mu. At this application rate, it can better reduce the content of available cadmium and mercury in the soil and reduce the accumulation of cadmium and mercury in various parts of rice (especially brown rice).

[0037] Further, in step S2, before thoroughly mixing the soil conditioner with the soil, adjust the soil water content to be not less than 100% of the field water holding capacity, and ensure that the water depth above the soil surface is 1 - 2 cm.

[0038] Further, in step S2, the balancing time is 7 - 10 days.

[0039] Further, in step S1, before applying it on the soil surface, mix the soil conditioner with fine mud or granulate it for later use.

[0040] Compared with the prior art, the present invention has the following advantages:

[0041] (1) The soil conditioner of the present invention is compounded with a pH regulator, sepiolite, phosphate, sulfate, iron-based antagonist, and zinc-based antagonist, which can effectively passivate cadmium and mercury combined pollution in the soil, reduce the absorption of cadmium and mercury by rice, improve the nutritional quality of rice at the same time, and has a stable effect when widely applied on a large scale;

[0042] (2) Using a controlled-release quicklime microsphere with a specific structure as the pH regulator can reversibly adjust the release rate of OH - according to the soil pH, so as to adapt to a wider soil pH range under a fixed addition amount, which is beneficial to the rapid passivation of cadmium and mercury combined pollution in the soil and the growth and development of rice. Description of the Drawings

[0043] Figure 1 Shows the effects of different soil conditioners on the Cd and Hg contents in the soil. Among them, Figure 1 (a) shows the effect on the Cd content in the soil; Figure 1 (b) shows the effect on the Hg content in the soil.

[0044] Figure 2 Shows the effects of different soil conditioners on the Cd and Hg contents in various parts of rice. Among them, Figure 2 (a) shows the effect on the Cd content in various parts of rice; Figure 2 (b) shows the effect on the Hg content in various parts of rice.

[0045] Figure 3 Shows the effect of different application rates of soil conditioners on the Cd content in the soil.

[0046] Figure 4 Shows the effect of different application rates of soil conditioners on the heavy Hg content in the soil.

[0047] Figure 5 Shows the effect of different application rates of soil conditioners on the Cd content in various parts of rice. Among them, in each part, from left to right are CK, L1, L2, L3, L4, and L5 in sequence.

[0048] Figure 6 Shows the effect of different application rates of soil conditioners on the Hg content in various parts of rice. Among them, in each part, from left to right are CK, L1, L2, L3, L4, and L5 in sequence.

[0049] Figure 7 Shows the effect of applying soil conditioners on the pH values of rhizosphere soil and non-rhizosphere soil.

[0050] Figure 8 Shows the effect of applying soil conditioners on the total Cd content of rhizosphere soil and non-rhizosphere soil.

[0051] Figure 9 Shows the effect of applying soil conditioners on the available Cd content of rhizosphere soil and non-rhizosphere soil.

[0052] Figure 10 Shows the effect of applying soil conditioners on the total Hg content of rhizosphere soil and non-rhizosphere soil.

[0053] Figure 11 Shows the effect of applying soil conditioners on the Cd content in various parts of rice.

[0054] Figure 12 Shows the effect of applying soil conditioners on the Hg content in various parts of rice.

[0055] Figure 13Effects of different pH regulators on the pH values of rhizosphere soil and non-rhizosphere soil.

[0056] Figure 14 Effects of different pH regulators on the available Cd content in rhizosphere soil and non-rhizosphere soil.

[0057] Figure 15 Effects of different pH regulators on the available Hg content in rhizosphere soil and non-rhizosphere soil.

[0058] Figure 16 Effects of different pH regulators on the Cd content in different parts of rice.

[0059] Figure 17 Effects of different pH regulators on the Hg content in different parts of rice. Specific implementation manners

[0060] The present invention will be further described below in conjunction with embodiments, but it does not define the protection scope of the present invention.

[0061] General embodiment

[0062] A soil conditioner for passivating cadmium and mercury combined pollution and improving the nutritional quality of rice, comprising the following components: a pH regulator, sepiolite, phosphate, sulfate, an iron-based antagonist, and a zinc-based antagonist.

[0063] As a specific implementation manner, the pH regulator includes quicklime and / or controlled-release quicklime microspheres; the controlled-release quicklime microspheres are composed of an amino quicklime core layer and a carboxylated polylactic acid shell layer coated outside the amino quicklime core layer.

[0064] As a specific implementation manner, the soil conditioner comprises the following components in parts by weight: 10-30 parts of quicklime or 10-50 parts of controlled-release quicklime microspheres, 10-30 parts of sepiolite, 10-30 parts of phosphate, 5-10 parts of sulfate, 3-8 parts of an iron-based antagonist, and 2-5 parts of a zinc-based antagonist.

[0065] As a specific implementation manner, the phosphate includes calcium magnesium phosphate fertilizer; the sulfate includes potassium sulfate; the iron-based antagonist includes ferric sulfate; the zinc-based antagonist includes zinc sulfate.

[0066] As a specific implementation manner, the preparation method of the controlled-release quicklime microspheres comprises the following steps:

[0067] (1) After making a mixed solution of an amino silane coupling agent and an anhydrous solvent, adding quicklime powder thereto, carrying out a dehydration condensation reaction, separating the product, and obtaining amino quicklime;

[0068] (2) mixing lactide, hydroxycitric acid and a catalyst, and performing a polymerization reaction in an oxygen-free environment to obtain carboxylated polylactic acid;

[0069] (3) dissolving the carboxylated polylactic acid and the cross-linking agent in a solvent to prepare a coating solution, spray coating the amino quicklime with the coating solution, and then curing and cross-linking to obtain controlled-release quicklime microspheres.

[0070] As a specific implementation method, the specific process of step (1) includes the following steps: preparing a mixed solution with an aminosilane coupling agent and an anhydrous solvent in a volume ratio of 1:10-20, adding quicklime powder in an amount of 0.05-0.25 g / mL, stirring the mixture at 20-30° C. for 1-2 h, separating the product, and obtaining amination quicklime.

[0071] As a specific implementation method, the specific process of step (2) includes the following steps: mixing lactide, hydroxycitric acid and zinc lactate in a mass ratio of 100:15-20:0.4-0.8, heating to 140-160°C in an anaerobic environment, and keeping the mixture warm for 24-36 hours to obtain carboxylated polylactic acid.

[0072] As a specific implementation method, the specific process of step (3) includes the following steps: mixing carboxylated polylactic acid, dicumyl peroxide (DCP) and solvent in a mass ratio of 1:0.001-0.003:3-5, stirring to dissolve, using the mixture as a coating liquid to spray-coat the amino quicklime, and then heat-treating at 120-130° C. for 20-30 min to obtain sustained-release quicklime microspheres.

[0073] The above-mentioned soil conditioner is used to passivate the combined pollution of cadmium and mercury in rice field soil and improve the nutritional quality of rice.

[0074] As a specific implementation, the application includes the following steps:

[0075] S1: After loosening the surface soil, spreading the soil conditioner on the soil surface;

[0076] S2: Mix the soil conditioner with the soil thoroughly and start planting rice after it is balanced.

[0077] As a specific implementation, in step S1, the application amount of the soil conditioner on the soil surface is 150-450 kg / mu.

[0078] As a specific implementation, in step S2, before the soil conditioner is fully mixed with the soil, the soil moisture content is adjusted to not less than 100% of the field water holding capacity to ensure that the water depth above the soil surface is 1-2 cm.

[0079] As a specific implementation manner, in step S2, the equilibration time is 7 to 10 days.

[0080] As a specific implementation manner, in step S1, before applying to the soil surface, the soil conditioner is mixed into fine mud or granulated and formed for later use.

[0081] Example 1: Effects of three soil conditioners on the safe production of rice and the iron and zinc contents in rice under cadmium and mercury combined pollution 1 Experimental plot

[0082] The experiment was carried out on an acidic paddy field in a certain place in Shaoxing City, Zhejiang Province. It belongs to the subtropical monsoon climate zone, with sufficient light and heat, abundant rainfall, mild climate, an average annual temperature of 16.4 °C, and an average annual rainfall of about 1446.8 mm. Before the experiment, the soil pH value of the 0-20 cm soil layer was 4.94, the organic matter content was 4.11%, the available nitrogen content was 174.33 mg·kg -1 , the available phosphorus content was 44.37 mg / kg, the available potassium was 151.38 mg·kg -1 , the total cadmium content was 0.44 mg·kg -1 , the total mercury content was 0.53 mg·kg -1 , according to the Risk Control Standards for Soil Pollution of Agricultural Land (GB 15618-2018), it belongs to slight cadmium-mercury pollution.

[0083] 2 Soil conditioner

[0084] The main components and dosages of the 3 soil conditioners (T1-T3) used in this experiment are shown in Table 1.

[0085] Table 1 Formulas and dosages of three soil conditioners

[0086]

[0087] 3 Application methods of soil conditioner

[0088] Three experimental groups were set up, using T1-T3 three soil conditioners respectively. After granulating and forming, they were reserved for later use. 5 days before planting, the surface 20 cm of soil was loosened by a rotary tiller. According to the dosages in Table 1, the soil conditioner was applied to the soil surface, and then the soil water content was adjusted to 100% of the field water holding capacity, ensuring that the water depth above the soil surface was 2 cm. A harrowing tool was used to fully mix the passivator on the loosened surface with the soil. After 7 days of equilibration, rice was planted. A randomized block design was adopted, with each plot area of 25 m 2 , each group was repeated 3 times. Dikes were built between plots and covered with plastic film to prevent seepage, and independent irrigation and drainage ditches were provided, without affecting each other. A control group (CK) was set up. Except for not applying the soil conditioner, other water, fertilizer and agronomic management measures were the same as those of the experimental groups.

[0089] 4 Testing

[0090] About 1 kg of rhizosphere soil samples of rice in each group were collected at the mature stage of rice, brought back to the laboratory, air-dried, then ground and passed through a 18-mesh sieve (for measuring the available content of elements) and a 100-mesh sieve (for measuring the total content of elements) respectively, packed in plastic-sealed bags, and the available and total contents of Cd and Hg were detected.

[0091] The rice plant samples were divided into three parts, namely roots, straws, and rice ears. After the plants were cleaned and dried, the fresh weight was weighed first, and then the dry weight was weighed after drying in an oven. The rice ears needed to be threshed after drying, and then shelled with a shelling machine, and then divided into two parts: chaff and brown rice, which were packed in envelopes and stored in a dry and ventilated place. The Cd and Hg contents in the roots, straws, chaff and brown rice were detected, and the Fe and Zn contents in the brown rice were also detected.

[0092] 5 Test Results

[0093] The Cd and Hg contents in the soil of the experimental group and the control group are shown in Figure 1 (a) and Figure 1 (b) respectively. It can be seen from them that:

[0094] (1) After applying the conditioner, the total Cd content in the soil did not change significantly compared with the control, while the available Cd content in the soil decreased significantly compared with the control group. Among them, after applying the T1, T2 and T3 conditioners, the exchangeable Cd content in the soil decreased by 26.89%, 31.42% and 26.33% respectively, indicating that all three conditioners had good effects on passivating soil Cd, but the differences among the three conditioners were not significant.

[0095] (2) Compared with the control, applying the conditioner had no significant effect on the total Hg content in the soil, but the available Hg content decreased significantly compared with the control. The decreases of T1-T3 were 48.77%, 56.17% and 65.43% in turn, indicating that all three conditioners had good effects on passivating soil Hg, but the differences among the three conditioners were not significant.

[0096] The Cd and Hg contents in each part of the rice in the experimental group and the control group are shown in Figure 2 (a) and Figure 2 (b) respectively. It can be seen from them that:

[0097] (1) Under the condition that the soil Cd and Hg contents were close, the Cd content in each part of the rice was significantly higher than the Hg content, indicating that the absorption, transportation and accumulation efficiency of Cd by rice was higher than that of Hg.

[0098] (2) For different parts of rice, the heavy metal content in the roots is much higher than that in the straw, husk, and brown rice. The Cd concentration shows the pattern of "root > straw > husk ≈ brown rice", and the Hg concentration shows the pattern of "root > straw ≈ husk ≈ brown rice".

[0099] (3) Compared with the control, the Cd and Hg contents in the roots, straw, husk, and brown rice of rice decreased to varying degrees after applying the conditioner. The Cd and Hg contents in the roots of T2 and T3 treatments were significantly lower than those of the control. The Cd concentration in the straw of T2 treatment was significantly lower than that of the control. After applying the conditioner (T1, T2, T3), the Cd content in the husk was significantly lower than that of the control. Compared with the control, the Cd contents in the brown rice of treatments T1 - T3 decreased by 44.31%, 49.67%, and 47.45% respectively, and the Hg contents decreased by 10.49%, 13.59%, and 9.01% respectively. According to the limit standards for contaminants in foods (GB 2762 - 2017), the limit standards for Cd and Hg in brown rice are both 0.2 mg·kg -1 ; the Cd content in the brown rice of the control was 0.34 mg·kg -1 , and the Hg content was 0.029 mg·kg -1 , both exceeding the national standards. After applying the conditioner, the Cd and Hg contents in the brown rice of each treatment of rice decreased to below 0.2 mg·kg -1 , reaching a safe level, indicating that all three soil conditioners had a positive effect on the safe production of rice.

[0100] The Fe and Zn contents in the brown rice of the experimental group and the control group of rice are shown in Table 2. It can be seen from this: The Fe and Zn contents in the brown rice under T3 treatment were significantly higher than those of the control. The Fe content in the brown rice was 4.1 times that of the control, and the Zn content was 1.7 times that of the control. It can be seen that the T3 conditioner can effectively increase the Fe and Zn contents in rice, and obtain agricultural products with higher nutritional quality.

[0101] Table 2 Effects of different conditioners on the nutritional quality of rice grains

[0102] Processing <![CDATA[Brown rice iron / mg·kg -1 > <![CDATA[Brown rice zinc / mg·kg -1 > CK <![CDATA[5.25±1.82 b > <![CDATA[36.18±1.09 b > T1 <![CDATA[5.95±0.29 b > <![CDATA[38.78±0.44 b > T2 <![CDATA[5.03±0.69 b > <![CDATA[39.46±0.19 b > T3 <![CDATA[21.57±5.74 a > <![CDATA[60.84±1.44 a >

[0103] Note: Different letters a and b represent significant differences, P ≤ 0.05.

[0104] To sum up, compared with soil conditioners T1 and T3, T3 reduces the dosage of quicklime and sepiolite, replaces them with calcium magnesium phosphate fertilizer, potassium sulfate, ferrous sulfate, and zinc sulfate. Under the same total dosage of soil conditioner, it will not cause a significant decline in the effect of passivating cadmium and mercury combined pollution, and at the same time can effectively improve the nutritional quality of rice grains.

[0105] Example 2: Effects of different dosages of soil conditioner on the safe production of rice and the iron and zinc contents in rice

[0106] 1 Experimental design

[0107] The test plot is the same as that in Example 1.

[0108] 2 Soil conditioner

[0109] The soil conditioner used in this example is composed of the following components by weight: 30 parts of quicklime (the main component is CaO, passing through a 100-mesh sieve), 30 parts of sepiolite (powdered clay mineral), 20 parts of calcium magnesium phosphate fertilizer, 10 parts of potassium sulfate, 3 parts of ferric sulfate, 2 parts of

[0110] zinc sulfate.

[0111] 3 Application method of soil conditioner

[0112] Set up four experimental groups L1 - L5, and the application rates of the soil conditioner are 75, 150, 300, 450, and 600 kg / mu respectively. The field application method is the same as that in Example 1; set up a control group (CK) without applying the soil conditioner. Other management measures are the same. Each group is repeated 3 times, and a completely randomized block design is adopted. The plot area is 25m 2 . Build a ridge between plots and cover it with plastic film to prevent seepage, and there are independent irrigation and drainage ditches.

[0113] 4 Testing

[0114] The testing method is the same as that in Example 1.

[0115] 5 Test results

[0116] The Cd contents in the soil of the experimental groups and the control group are shown in Figure 3 , from which it can be seen that: there is no significant difference in the total Cd content of the soil between the experimental groups and the control group, which is roughly in the range of 0.4 - 0.45 mg·kg -1 . Compared with the control, the available Cd in the soil has decreased after applying the conditioner, and the available Cd contents in L2 and L3 are significantly reduced. As the application rate increases, the proportion of available Cd in the soil to total Cd first decreases, then increases, and then remains unchanged. The reason may be that the organic matter content in the soil affects the availability of cadmium. Therefore, the larger the application rate, although it can increase the soil pH value more, it may also change the physical and chemical properties of the soil, resulting in an increase in the available Cd content instead.

[0117] The Hg contents in the soil of the experimental groups and the control group are shown in Figure 4, from which it can be seen that there is no significant difference in the total Hg content of the soil between the experimental group and the control group. This indicates that the mercury content in the soil of the plots where the six treatments are located is similar. Subsequently, the effect of the conditioner on solidifying Hg can be judged by comparing the Hg content in rice. Moreover, with the increase in the application rate, the total Hg content in the soil does not show an upward trend, indicating that the added conditioner may not contain the pollutant Hg.

[0118] The Cd and Hg contents of each part of the rice in the experimental group and the control group are shown respectively in Figure 5 and Figure 6 , from which it can be seen that:

[0119] (1) The Cd content in the roots of rice under different treatments is between 2.7 - 3.6 mg / kg, which is higher than the Cd content in the soil; while the Hg content in the roots of rice under different treatments is between 0.2 - 0.5 mg / kg, which is similar to the Hg content in the soil. As described in Example 1, this is because the mobility of Hg is poorer than that of Cd. With the increase in the application rate, the Cd content in the roots of rice first decreases and then increases, and this trend is the same as the change trend of the available Cd content in the soil. Compared with the control, the Hg content in the roots of the treatments with the conditioner applied is significantly reduced, and with the increase in the application rate, the Hg content in the roots first increases and then decreases.

[0120] (2) The Cd content in the straw under different treatments is roughly in the range of 0.55 - 0.70 mg / kg, while the Hg content is between 0.018 - 0.21 mg / kg. The Cd and Hg contents of the rice straw under different treatments are reduced to varying degrees compared with the control. With the increase in the application rate, the Cd and Hg concentrations in the straw first decrease and then increase. This may be because the Cd in the straw is transferred from the roots in the underground part, and the lower Cd content in the roots leads to a corresponding lower Cd content in the straw. For Hg, due to the poor mobility of Hg and the not very large difference in the Hg content in the straw, the change trend of the straw is not the same as that of the roots.

[0121] (3) Compared with the control, the Cd content in the chaff of the treatments with the conditioner applied is significantly reduced, and the Hg content in the chaff of L4 and L5 is significantly reduced. With the increase in the application rate, the Cd and Hg contents in the chaff first decrease, then increase, and then decrease again.

[0122] (4) For the most important brown rice part of rice, after applying the conditioner, the Cd and Hg contents are significantly lower than those of the control group. Compared with the Cd content of 0.345 mg / kg in the control group, the Cd contents of brown rice in different treatments are reduced by 43.00%, 49.67%, 50.71%, 50.23%, and 47.85% respectively; compared with the Hg content of 0.024 mg / kg in the control group, the Hg contents of brown rice in different treatments are reduced by 22.94%, 24.07%, 28.58%, 25.01%, and 21.87% respectively. According to the national limit standard, the brown rice of rice grown on the soil after applying the conditioner does not exceed the standard. Therefore, applying the conditioner can reduce the risk of Cd and Hg exceeding the standard in crops. As the application rate increases, the Cd and Hg contents in brown rice also show a trend of first decreasing and then increasing. This may be because the absorption of Cd and Hg by plants from the soil is affected not only by the pH value, but also by the cation exchange capacity, organic matter content of the soil, and the interaction between ions. Applying too much strongly alkaline conditioner will change the physical and chemical properties of the soil, so the effect of solidifying heavy metals becomes worse.

[0123] The Fe and Zn contents in the brown rice of the experimental group and the control group of rice are shown in Table 3. It can be seen from the table that although most of them do not reach the significant level, the Fe and Zn contents in the brown rice after applying the conditioner are mostly higher than those of the control group, and the overall treatment effects of L2 and L3 are the best.

[0124] Table 3 Effects of different conditioners on the nutritional quality of rice grains

[0125] Processing <![CDATA[Brown rice iron / mg·kg -1 > <![CDATA[Brown rice zinc / mg·kg -1 > CK <![CDATA[5.6 b > <![CDATA[36.02 a > L1 <![CDATA[7.2 a > <![CDATA[36.18 a > L2 <![CDATA[6.6 ab > <![CDATA[39.46 a > L3 <![CDATA[8.0 a > <![CDATA[39.97 a > L4 <![CDATA[6.9 ab > <![CDATA[35.65 a > L5 <![CDATA[7.4 ab > <![CDATA[36.32 a >

[0126] Note: Different letters a and b represent significant differences, P ≤ 0.05.

[0127] Example 3: Demonstration study on the safe production of rice by soil conditioner

[0128] 1 Test plot

[0129] The test plot is the same as that in Example 1.

[0130] 2 Soil conditioner

[0131] The soil conditioner used in this example is composed of the following components in parts by weight: 30 parts of quicklime (the main component is CaO, passing through a 100-mesh sieve), 30 parts of sepiolite (powdered clay mineral), 20 parts of calcium magnesium phosphate fertilizer, 10 parts of potassium sulfate, 3 parts of ferric sulfate, and 2 parts

[0132] zinc sulfate.

[0133] 3 Application method of soil conditioner

[0134] An experimental group (D) was set up with the application rate of the soil conditioner being 300 kg / mu, and the application method was the same as that in Example 1; a control group (CK) was set up without applying the soil conditioner. All other management measures were the same. The test area was 5 mu for each group.

[0135] 4 Testing

[0136] At the rice maturity stage, the Cd and Hg contents in the rhizosphere soil, non-rhizosphere soil and various parts of the rice were detected by the same method as in Example 1, and the pH values of the rhizosphere soil and non-rhizosphere soil were detected.

[0137] 5 Test Results

[0138] The pH values of the rhizosphere soil and non-rhizosphere soil in the experimental group and the control group are shown in Figure 7 , from which it can be seen that:

[0139] (1) Compared with the control, the application of the conditioner can increase the soil pH value, and the soil pH value of the rhizosphere soil is significantly increased. This is because the applied conditioner contains more alkaline lime, so it can change the soil pH value.

[0140] (2) Whether the conditioner is applied or not, the pH value of the rhizosphere soil is less than that of the non-rhizosphere soil. This is because in order to activate some nutrient elements (such as iron) in the soil, the root system will actively secrete some reducing substances. While releasing electrons, the root also releases protons (H + ), to acidify the rhizosphere soil to achieve the purpose of absorbing nutrient elements. The root system will also secrete organic acids to chelate the elements in the soil. In addition, the root system and rhizosphere microorganisms will produce CO 2 through respiration, which will also reduce the pH value of the rhizosphere soil.

[0141] The total Cd content and available Cd content in the rhizosphere soil and non-rhizosphere soil of the experimental group and the control group are shown in Figure 8 and 9 , from which it can be seen that:

[0142] (1) There is no significant difference in the total Cd content in the rhizosphere soil and non-rhizosphere soil between the experimental group and the control group, which is roughly 0.43 - 0.48 mg / kg. However, compared with the control, whether it is the rhizosphere soil or the non-rhizosphere soil, the application of the conditioner can reduce the available Cd content in the soil.

[0143] (2) The available Cd content in the rhizosphere soil is lower than that in the non-rhizosphere soil. This may be because the migration process of available Cd in the soil and rice includes migration from the non-rhizosphere to the rhizosphere, rice absorption, rhizosphere activation, etc. Since the absorption rate of available Cd in the rhizosphere by rice is greater than the rate of rhizosphere activation and migration from the non-rhizosphere to the rhizosphere, the available Cd content in the rhizosphere soil is lower than that in the non-rhizosphere soil.

[0144] The total Hg contents in the rhizosphere soil and non-rhizosphere soil of the experimental group and the control group are shown in Figure 10 , from which it can be seen that: there is no significant difference in the total Hg content in the rhizosphere soil and non-rhizosphere soil between the experimental group and the control group, and it is roughly 0.40 - 0.44 mg / kg. This indicates that the mercury content in the soil body is similar among the sampling points in the field, so the effect of the conditioner on solidifying Hg can be judged by comparing the Hg content in rice.

[0145] The Cd and Hg contents in each part of the rice in the experimental group and the control group are shown in Figure 11 and Figure 12 , from which it can be seen that:

[0146] (1) The Cd content in the rice husk and brown rice of the experimental group is significantly lower than that of the control. Compared with the control, the Cd contents in the roots, straws, rice husks, and brown rice of the rice in the experimental group are reduced by 10.14%, 17.84%, 36.13%, and 51.04% respectively, indicating that the effect of the conditioner on solidifying Cd in the experimental group is quite remarkable. The Cd content in the brown rice of the control group is about 0.29 mg / kg, while the Cd content in the brown rice of the experimental group is about 0.14 mg / kg. According to the national limit standard, the cadmium content in brown rice shall not exceed 0.2 mg / kg, so the cadmium content in brown rice can meet the standard after applying the conditioner. Therefore, from the perspective of the content of heavy metal Cd, safe production of rice can be achieved in the demonstration area where the conditioner is applied.

[0147] (2) The Hg contents in the roots, rice husks, and brown rice of the experimental group are significantly lower than that of the control. Compared with the control, the Hg contents in the roots, straws, rice husks, and brown rice of the rice in the experimental group are reduced by 42.08%, 12.46%, 22.15%, and 20.16% respectively. According to Figure 10 it is known that the Hg content in the soil body is similar, indicating that the effect of the conditioner on solidifying Hg in the experimental group is quite remarkable. According to the national limit standard, that is, the Hg content in brown rice shall not exceed 0.02 mg / kg. The Hg content in the brown rice of the control area exceeds the standard, about 0.022 mg / kg, while the Hg content in the brown rice of the demonstration area is about 0.018 mg / kg. Although the reduction range is not as high as that of Cd, it has met the standard. Therefore, from the perspective of the content of heavy metal Hg, safe production of rice can be achieved in the demonstration area where the conditioner is applied.

[0148] Example 4: Influence of different pH regulators on safe production of rice

[0149] 1 Experimental design

[0150] Test plot 1: The same as in Example 1.

[0151] Test plot 2: The soil pH of the same test plot as in Example 1 is adjusted to 4.36 with hydrochloric acid solution.

[0152] 2 Soil Conditioner

[0153] Soil conditioner 1 is composed of the following components by weight: 30 parts of quicklime (the main component is CaO, passing through a 100-mesh sieve), 30 parts of sepiolite (powdered clay mineral), 20 parts of calcium magnesium phosphate fertilizer, 10 parts of potassium sulfate, 3 parts of ferric sulfate, and 2 parts of zinc sulfate.

[0154] Soil conditioner 2 is composed of the following components by weight: 50 parts of controlled-release quicklime microspheres, 30 parts of sepiolite (powdered clay mineral), 20 parts of calcium magnesium phosphate fertilizer, 10 parts of potassium sulfate, 3 parts of ferric sulfate, and 2 parts of zinc sulfate. Among them, the controlled-release quicklime microspheres are prepared by the following steps:

[0155] (1) Prepare a mixed solution of silane coupling agent KH-550 and ethanol in a volume ratio of 1:10, add quicklime powder (the main component is CaO, passing through a 100-mesh sieve) to it at an addition amount of 0.15 g / mL, stir and react at 25 °C for 1.5 h, carry out suction filtration, wash with ethanol, dry, grind, and then pass through a 100-mesh sieve to obtain aminoated quicklime with a particle size less than 100 mesh;

[0156] (2) Mix L-lactide, hydroxycitric acid, and zinc lactate in a mass ratio of 100:20:0.6, heat to 150 °C under nitrogen protection, and keep the temperature for reaction for 24 h to obtain carboxylated polylactic acid;

[0157] (3) Mix carboxylated polylactic acid, DCP, and N,N-dimethylformamide (DMF) in a mass ratio of 1:0.001:3, stir and dissolve it, use it as a coating solution to spray-coat the aminoated quicklime, then carry out heat treatment at 125 °C for 20 min, soak in ether and ethanol for 15 min respectively to remove DCP, dry, and then screen with 80-mesh and 120-mesh sieves in sequence to obtain controlled-release quicklime microspheres with a particle size of 70-120 mesh.

[0158] Soil conditioner 3 is composed of the following components by weight: 50 parts of controlled-release quicklime microspheres, 30 parts of sepiolite (powdered clay mineral), 20 parts of calcium magnesium phosphate fertilizer, 10 parts of potassium sulfate, 3 parts of ferric sulfate, and 2 parts of zinc sulfate. Among them, the controlled-release quicklime microspheres are prepared by the following steps:

[0159] (1) The same as step (1) in the preparation process of the controlled-release quicklime microspheres in soil conditioner 2;

[0160] (2) The same as step (2) in the preparation process of the controlled-release quicklime microspheres in soil conditioner 2;

[0161] (3) Mix carboxylated polylactic acid and DMF at a mass ratio of 1:3, stir and dissolve them, and use the resulting solution as a coating solution to spray-coat amino-calcium oxide. After drying, screen the product successively through 80-mesh and 120-mesh sieves to obtain slow-release calcium oxide microspheres with a particle size of 70-120 mesh.

[0162] 3 Application method of soil conditioner

[0163] Set up four experimental groups F1-F6: F1-F3 are carried out on test plot 1, and F4-F6 are carried out on test plot 2; F1 and F4 are applied with soil conditioner 1, F2 and F5 are applied with soil conditioner 2, and F3 and F6 are applied with soil conditioner 3. Among them, the application rate of soil conditioner 1 is 300 kg / mu, and the application rates of soil conditioners 2 and 3 are both 363 kg / mu (control the application rates of other components except calcium oxide to be equal), and the application method is the same as that in Example 1. Each group is repeated 3 times, and a completely randomized block design is adopted. The plot area is 25 m 2 . Build ridges between plots, cover them with plastic films to prevent seepage, and set up independent irrigation and drainage ditches.

[0164] 4 Testing

[0165] The testing method is the same as that in Example 3.

[0166] 5 Test results

[0167] The pH values of the rhizosphere soil and non-rhizosphere soil of each experimental group are shown in Figure 13 . It can be seen from this that the soil pH values of F2 and F5 are similar, while the soil pH values of F1 and F4 differ greatly, indicating that compared with calcium oxide, the controlled-release calcium oxide microspheres can adapt to a wider range of soil pH values at a fixed application rate and can adjust the soil with different initial pH values to an appropriate acidity and alkalinity without adjusting the application rate.

[0168] The contents of available Cd and available Hg in the rhizosphere soil of each experimental group are shown in Figure 14 and 15 . It can be seen from this that:

[0169] (1) The contents of available Cd and Hg in the soil of F2 and F5 are similar, while the content of available Hg in the soil of F4 is significantly higher than that of F1, indicating that compared with calcium oxide, the controlled-release calcium oxide microspheres can adapt to a wider range of soil pH values at a fixed application rate, which is beneficial to the passivation of Hg in the soil.

[0170] (2) The available Hg content in the soil of F5 is similar to that of F2, while the available Hg content in the soil of F6 is significantly higher than that of F3, indicating that when applied to acidic soils, the carboxylated polylactic acid shell of the controlled-release quicklime microspheres is cured and crosslinked, which is beneficial to the passivation of Hg in the soil. This may be because when applied to acidic soils, the combination between the core and shell of the controlled-release quicklime microspheres is relatively loose, and the core layer is prone to irreversible damage and difficult to recover to a dense coating state after the soil pH increases. OH - is still rapidly released, resulting in too high soil pH and excessive reproduction of sulfate-reducing bacteria, and then a large amount of methylmercury is produced; while curing and crosslinking the carboxylated polylactic acid shell can avoid irreversible damage to the core layer in acidic soils.

[0171] The Cd and Hg contents in each part of the rice in each experimental group are shown in Figure 16 and 17 respectively, from which it can be seen that:

[0172] (1) The Cd and Hg contents in the rice of F2 and F5 are similar, and the Cd and Hg contents in the rice of F4 are higher than those of F1, indicating that compared with quicklime, the controlled-release quicklime microspheres can adapt to a wider range of soil pH values under a fixed application rate, which is beneficial to reducing the absorption and accumulation of Cd and Hg by rice.

[0173] (2) The Hg content in the rice of F2 is similar to that of F5, while the Hg content in the rice of F6 is higher than that of F3, indicating that when applied to acidic soils, the carboxylated polylactic acid shell of the controlled-release quicklime microspheres is cured and crosslinked, which is beneficial to reducing the absorption and accumulation of Cd and Hg by rice.

[0174] In the present invention, the raw materials and equipment used are all common raw materials and equipment in the field without special instructions; the methods used in the present invention are all conventional methods in the field without special instructions.

[0175] The above are only the preferred embodiments of the present invention, and do not limit the present invention in any way. Any simple modifications, changes and equivalent transformations made to the above embodiments according to the technical essence of the present invention still belong to the protection scope of the technical solution of the present invention.

Claims

1. A soil conditioner for passivating cadmium and mercury combined pollution and improving the nutritional quality of rice. It is characterized in that include: Controlled-release quicklime microspheres, sepiolite, phosphate, sulfate, iron-based antagonist, zinc-based antagonist; the controlled-release quicklime microspheres are composed of an amino quicklime core layer and a carboxylated polylactic acid shell layer coated on the amino quicklime core layer, specifically: an aminosilane coupling agent and anhydrous solvent are made into a mixed solution, quicklime powder is added, a dehydration condensation reaction is carried out, and the product is separated to obtain the amino quicklime; lactide, hydroxycitric acid and a catalyst are mixed, and a polymerization reaction is carried out in an oxygen-free environment to obtain carboxylated polylactic acid; carboxylated polylactic acid and a cross-linking agent are dissolved in a solvent to prepare a coating solution, the amino quicklime is spray-coated with the coating solution, and then solidified and cross-linked to obtain the controlled-release quicklime microspheres.

2. The soil conditioner according to claim 1, It is characterized in that The invention comprises the following components in parts by weight: 10-50 parts of controlled-release quicklime microspheres, 10-30 parts of sepiolite, 10-30 parts of phosphate, 5-10 parts of sulfate, 3-8 parts of iron-based antagonist and 2-5 parts of zinc-based antagonist.

3. The soil conditioner according to claim 1, It is characterized in that The phosphate includes calcium magnesium phosphate; the sulfate includes potassium sulfate.

4. The soil conditioner according to claim 1, It is characterized in that The iron-based antagonist includes iron sulfate; the zinc-based antagonist includes zinc sulfate.

5. Use of the soil conditioner according to any one of claims 1 to 4 for passivating the combined pollution of cadmium and mercury in rice field soil and improving the nutritional quality of rice.

6. The use according to claim 5, It is characterized in that The following steps are involved: S1: After loosening the surface soil, spreading the soil conditioner on the soil surface; S2: Mix the soil conditioner with the soil thoroughly and start planting rice after it is balanced.

7. The use according to claim 6, It is characterized in that In step S1, the application amount of the soil conditioner on the soil surface is 150-450 kg / mu.

8. The use according to claim 6, It is characterized in that In step S2, before the soil conditioner is fully mixed with the soil, the soil moisture content is adjusted to not less than 100% of the field water holding capacity, ensuring that the water depth above the soil surface is 1-3 cm.

9. The use according to claim 6, It is characterized in that In step S1, before spreading on the soil surface, the soil conditioner is mixed into fine mud or granulated into particles for later use.

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