Field placing method for reducing mercury content of brown rice in light and moderate mercury pollution rice field

Abstract

A field placing method for reducing mercury content of brown rice in a light and moderate mercury pollution rice field comprises the steps that after rice transplanting is conducted for 30-40 days, intermittent field placing is started at the last tillering stage, no matter whether rainfall exists or not, it is guaranteed that the total drying day number reaches 10 days, and the field placing degree is based on farmland cracks, rice leaves stretch upwards in a sword shape and touch and prick hands slightly; after the ripening period is finished, field placing is conducted, irrigation is stopped, and the rice field naturally falls dry; water is controlled in the growth period, wherein wet irrigation is carried out from the heading period to the end of grouting, and the irrigation water layer does not exceed 2 cm every time. The field placing method provided by the invention not only is an environment-friendly agricultural practice, but also shows a remarkable synergistic effect in the aspects of guaranteeing grain safety and improving rice quality, and provides a new thought and an effective way for solving the problem of heavy metal pollution in rice production.

Description

Technical Field

[0001] The invention belongs to the technical field of heavy metal pollution prevention and control of crops, and specifically relates to a method for reducing the mercury content of brown rice in rice fields with light to moderate mercury pollution. Background Art

[0002] Mercury (Hg) is one of the most toxic heavy metal pollutants in the world and is widely distributed in a variety of environmental media, among which soil is the largest storage place for mercury in the world. In the world, the severity of soil mercury pollution in the northern half is higher than that in the southern half. Mercury in soil can be divided into elemental mercury, inorganic compound state and organic compound state. Inorganic mercury is easily converted into neurotoxic methylmercury (MeHg) by some sulfur-reducing bacteria, some iron-reducing bacteria and methanogens under anaerobic conditions. A large number of studies have shown that methylmercury in rice grains mainly comes from soil, and methylmercury in soil is mainly formed by in situ methylation of inorganic mercury. However, irrigation is necessary during the growth of rice. After irrigation, the redox potential of the soil changes, which affects the formation of manganese / iron compounds in the soil and its adsorption of mercury. The long-term wetland state of the irrigated rice field enhances the activity of anaerobic microorganisms and increases the production of methane, making it an active place for methylmercury. Therefore, compared with other crops, rice absorbs and accumulates more mercury, and there is a high risk of exceeding the standard.

[0003] Current research results show that proper soil moisture management is one of the important ways to reduce the accumulation of total mercury in crop grains in mercury-contaminated areas. However, water layer irrigation is generally required for rice cultivation in paddy fields, not only to ensure the water demand of rice during the growth cycle, but also to create an ecological environment suitable for rice growth and development. Under flooding conditions, the soil is in a reduced state, organic matter decomposes more slowly and accumulates more easily, which is conducive to soil fertility conservation and fertilizer supply. Therefore, using unreasonable field-leaving measures to regulate rice moisture may cause a decrease in rice yield. Summary of the invention

[0004] Technical problem to be solved: In order to solve the problem that during the rice production process, continuous flooding during the entire growth period will aggravate the mercury pollution in the rice fields, the absorption and accumulation of mercury by rice, and ultimately lead to excessive mercury content in brown rice. The present invention provides a method for reducing the mercury content in brown rice in rice fields with mild to moderate mercury pollution, which can effectively reduce the mercury content in brown rice without significantly affecting the yield of the rice variety.

[0005] Technical solution: A method for reducing the mercury content of brown rice in lightly to moderately mercury-contaminated rice fields by leaving the fields idle, the steps comprising: 30 to 40 days after transplanting, intermittently leaving the fields starting at the end of tillering, ensuring that the total number of days of drying out reaches 10 days regardless of whether there is precipitation, and the degree of leaving the fields is based on cracks in the fields, and the rice leaves stretching upward in a sword shape and being prickly to the touch; leaving the fields idle after the waxy stage, stopping irrigation, and allowing the rice fields to dry out naturally; controlling water during the growth period: applying moist irrigation from the heading stage to the end of filling, with the water layer not exceeding 2 cm each time.

[0006] Preferably, the soil mercury concentration of the above-mentioned lightly to moderately mercury-contaminated rice fields is 0.6 to 1.6 mg / kg.

[0007] Preferably, the fields are left idle after the wax maturity period and drained in case of rain.

[0008] Preferably, water is controlled during the above growth period and drainage is carried out in time to prevent the rice fields from maintaining a high water level for a long time after precipitation, that is, the water layer does not exceed 2 cm.

[0009] Preferably, the above rice variety is Suxiangjing (Sujing) 1176, Chunyou 927, Ningxiangjing 9, Changxiangjing 1813, Xiushui 121 or Nanjing 46.

[0010] Preferably, the above-mentioned field-leaving method is suitable for the southern Jiangsu region.

[0011] Preferably, the rice is additionally applied with a herbicide at least once after transplanting.

[0012] Beneficial effects: The field-leaving method described in the present invention is specially designed for rice fields in Jiangsu and Zhejiang provinces, demonstrating an innovative agricultural management strategy that aims to achieve a dual increase in yield and quality, and embodies a significant synergistic effect. The core of this method is that by scientifically regulating the water management of rice fields, that is, implementing appropriate field-leaving measures at specific growth stages, not only the normal growth and development of rice and stable yield are ensured, but more importantly, this measure effectively promotes the natural degradation and migration of harmful elements in the soil such as mercury, and significantly reduces the mercury content in brown rice, thereby improving the edible safety and health quality of rice. Specifically, during the field-leaving process, moderate soil drying is conducive to the enhancement of soil microbial activity. These microorganisms can convert or fix part of the mercury element in metabolic activities, reducing the chance of it being absorbed by the rice root system. At the same time, the improvement of the physical and chemical properties of the soil also promotes the transformation of mercury forms and reduces its biological effectiveness. In addition, the paddy field also promotes the deep rooting and strengthening of the rice root system, enhances the plant's ability to efficiently absorb and utilize nutrients, and indirectly improves the rice's resistance to adverse environmental conditions, including the ability to resist heavy metal pollution, further ensuring the simultaneous improvement of rice yield and quality. In summary, the paddy field method proposed in the present invention is not only an environmentally friendly agricultural practice, but also shows a significant synergistic effect in ensuring food security and improving rice quality, providing a new idea and effective way to solve the problem of heavy metal pollution in rice production. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 This is a comparison chart of the mercury content in brown rice of Suxiangjing (Sujing) 1176 under different field-resting methods in the field survey in Example 1.

[0014] Figure 2 This is a comparison chart of the mercury content in brown rice of Nanjing 3908 under different field-resting methods in the field survey in Example 1.

[0015] Figure 3 This is a comparison chart of the mercury content and BCF (bioconcentration factor) of Changxiangjing 1813 brown rice under different field resting methods in Example 2.

[0016] Figure 4 This is a comparison chart of the yield of Changxiangjing 1813 under different land-resting methods in Example 2.

[0017] Figure 5 This is a comparison chart of the mercury content in brown rice of five different rice varieties under different field-resting methods in Example 2.

[0018] Figure 6 The graph is a comparison of the yields of five different rice varieties under different landfill methods in Example 2.

[0019] Figure 7This is a comparison chart of the mercury content and cumulative amount in Xiushui 121 plants under different water layer height conditions in Example 3.

[0020] Figure 8 This is a comparison chart of the mercury content of Nanjing 46 brown rice under four types of field resting methods in Example 4.

[0021] Fig. 9 This is a comparison chart of the yield of Nanjing 46 under the four land-leaving methods in Example 4.

[0022] Figure 1 The asterisks in the bar graph are annotated as follows:

[0023] *- indicates the results of independent sample T test analysis, P value <0.05, and there is a statistically significant difference between the two groups of data.

[0024] Figure 2 , Figure 4 and Fig. 9 The letters in the bar graph are annotated as follows:

[0025] NS- indicates no significant difference among the included data. DETAILED DESCRIPTION

[0026] The present invention discloses a method for reducing the mercury content of rice in rice fields with mild to moderate mercury pollution. In order to better explain the present invention, the present invention is described in detail below in conjunction with specific implementation cases.

[0027] Example 1

[0028] Trial time: October 2021

[0029] Test location: Southern Jiangsu

[0030] This example is a field survey sampling. Field sampling of two different rice varieties was conducted in southern Jiangsu in October 2021, during the rice harvest season.

[0031] ①Plot 1

[0032] Rice variety: Suxiangjing (Sujing) 1176

[0033] Soil properties: pH is 6.43; soil mercury content is 1.02 mg / kg.

[0034] Time to leave the field: 30 to 40 days after transplanting

[0035] ②Plot 2

[0036] Rice variety: Nanjing 3908

[0037] Soil properties: pH is 5.96; soil mercury content is 2.32 mg / kg.

[0038] Time to leave the field: 30 to 40 days after transplanting

[0039] Figure 1 and Figure 2 The criteria for the idle field group were that the soil surface turned white and the cultivated land was cracked during the rice harvest period; the criteria for the flooded group were that the soil was still slightly moist during the rice harvest period.

[0040] The field sampling mainly found that under different water and fertilizer management conditions in lightly and moderately mercury-contaminated farmland, Suxiangjing 1176 ( Figure 1 ) There was a statistically significant difference in the mercury content of brown rice; Nanjing 3908 ( Figure 2 )There was no significant difference in the mercury content of brown rice.

[0041] Example 2

[0042] This example is divided into two blocks. One block is for comparing flooding and field-leaning treatments; the other block is for comparing the reduction of mercury content in five rice varieties under field-leaning conditions. Each treatment is a 3-replicate randomized block experiment.

[0043] Trial period: June to November 2022

[0044] Test location: Southern Jiangsu

[0045] Soil properties: pH is 6.68±0.17; soil mercury content is 0.89±0.13 mg / kg.

[0046] ① Water management area group

[0047] Rice variety: Changxiangjing 1813

[0048] Flooding treatment: Leave the field for about 8 days at the end of tillering. The degree of leaving the field is not high and the soil is not cracked. Leave the field after the waxy maturity period, that is, stop irrigating after the filling is completed. Drain the water when it rains and let the rice field dry naturally. Keep the water layer above 5cm during the growth period.

[0049] Field treatment: Fields should be left idle for about 10 days at the end of tillering. The degree of left idle is that the fields are cracked, the rice leaves stretch upward in a sword shape and are prickly to the touch. Fields should be left idle after the waxy maturity period, that is, no more irrigation is done after the filling is completed. When it rains, the fields should be drained to allow the rice fields to dry naturally. During the growth period, the water layer should be kept above 2 cm for irrigation and the fields should be exposed appropriately.

[0050] In the water management area group, under the condition that the rice variety was the same, Changxiangjing 1813, the mercury and bioaccumulation coefficient of brown rice were significantly different ( Figure 3 ), while there was no statistically significant difference in yield ( Figure 4). Compared with the flooded group, the mean mercury content of brown rice in the field-leaving group was reduced by 59.38%; the mean mercury content of brown rice in the field-leaving group was 37.5% lower than the national standard limit (GB 2762-2022 "National Food Safety Standard Limits of Contaminants in Food", mercury content in brown rice <20μg / kg).

[0051] ②Selection blocks for varieties treated with field leave

[0052] Rice varieties: Chunyou 927, Ningxiangjing 9, Changxiangjing 1813, Xiushui 121 and Nanjing 3908

[0053] Water management during the growing period: the same as the field-lean treatment in the water management block group experiment.

[0054] Under the field-leave treatment, Ningxiangjing 9 had the lowest bioaccumulation factor compared with the other four rice varieties ( Figure 5 ), which was significantly lower than that of Chunyou 927, Changxiangjing 1813, Xiushui 121 and Nanjing 3908 (p < 0.05). The mercury content of brown rice of Chunyou 927, Ningxiangjing No. 9, Changxiangjing 1813 and Xiushui 121 did not exceed the standard (brown rice mercury < 20 μg / kg); only the mercury content of brown rice of Nanjing 3908 exceeded the standard under the field-leaving treatment, which also confirmed the result that there was no significant difference in the mercury content of brown rice of Nanjing 3908 under the field-leaving and flooding conditions in the field sampling of Example 2 ( Figure 2 ), it is speculated that the technical method of reducing the mercury content in brown rice by leaving the rice field idle is only applicable to some rice varieties, and other rice varieties need to be verified through experiments.

[0055] Compared with the approved per mu yield in Jiangsu Province, the field-leaving treatment did not have a significant impact on the yield of the five rice varieties ( Figure 6 ).

[0056] Example 3

[0057] This example is a potted rice flooding experiment. The experimental design is to use mildew-proof and waterproof glass glue to raise the ceramic pots under the same soil background value, environmental temperature and humidity, fertilization and pesticide spraying, and rice variety (i.e., Xiushui 121) conditions to ensure that the maximum water layer height during the rice growth period is 3cm, 6cm, and 9cm respectively. Each treatment is a 3-repetition randomized block experiment, hereinafter referred to as 3cm, 6cm, and 9cm.

[0058] Test location: Jiaxing City, Zhejiang Province

[0059] Soil collection location: Southern Jiangsu

[0060] Trial period: June to November 2022

[0061] Soil properties: pH is 4.76; soil mercury content is 0.68 mg / kg.

[0062] The specific test points of the three treatments are as follows:

[0063] 3cm - Ensure that the water layer height of Xiushui 121 is maintained at 3cm for a long time during its growth and development period. When the water level drops to the point where the soil surface is slightly cracked, irrigate again to the 3cm water level.

[0064] 6cm-Ensure that the water layer height of Xiushui 121 is maintained at 3-6cm for a long time during the growth and development period. Each time the 3cm treatment block group is irrigated, the 6cm block group is also irrigated to the maximum water layer height, i.e. 6cm. Prevent the water level from dropping below 3cm during the growth and development period of rice.

[0065] 9cm-Ensure that the water layer height of Xiushui 121 is maintained at 6-9cm for a long time during the growth and development period. Each time the 3cm treatment block group is irrigated, the 9cm block group is also irrigated to the maximum water layer height, i.e. 9cm. Prevent the water level from dropping below 6cm during the growth and development period of rice.

[0066] The total mercury content of rice roots, stems, leaves, brown rice and husks was tested during the harvest period. Figure 7 ), and calculate the amount of mercury accumulation in tissues according to the following formula.

[0067] Mercury accumulation in rice tissue (μg) = mercury content in rice tissue (μg / kg) × dry weight (kg)

[0068] The results of the pot experiment showed that there was no significant difference in the mercury content of roots, stems, leaves, brown rice and husks among the three treatments; the mercury accumulation in leaf tissues in the 3 cm area group was significantly lower than that in the 6 cm and 9 cm area groups, indicating that the higher irrigation height significantly increased the dry weight of rice leaf tissues, but did not increase the dry weight of rice. Therefore, under the experimental conditions, the water layer height was not the most important factor affecting the total mercury content of brown rice. Frequent field exposure and increased water layer height failed to produce significant differences in the mercury content of brown rice under different water control treatments.

[0069] Example 4

[0070] Trial period: June to November 2023

[0071] Test location: Southern Jiangsu

[0072] Rice variety: Nanjing 46

[0073] Soil properties: pH 5.96±0.13; soil mercury content 1.39±0.18 mg / kg

[0074] Experimental design: There are 4 plots (represented by the field-laying methods 1, 2, 3, and 4, hereinafter referred to as methods 1, 2, 3, and 4), each with an area of ​​540 m 2(60m long × 9m wide), the ridges between plots are 1m wide. The ditches between plots are 50cm wide and 40cm deep. After the start of the landfill in methods 1, 2, and 3, the landfill was flooded for 2 days after being left idle for 2 days due to natural precipitation, and the expected continuous landfill was not achieved, but the total number of days of landfill was 10 days.

[0075] The specific methods of leaving farmland in the four communities are as follows:

[0076] Method 1: Leave the field idle at the end of tillering, drain for 2 days, flood for 2 days, and then drain for 8 days. The total number of days of drying is about 10 days. Slightly control water from the heading stage, and often expose the field until the filling is completed. Leave the field idle after the waxy stage, that is, stop irrigating after the filling is completed, and drain when it rains, so that the rice field can dry naturally.

[0077] Method 2: Leave the field idle at the end of tillering, drain for 2 days, flood for 2 days, and then leave the field idle for 8 days, with a total of about 10 days of dry days; leave the field idle after the waxy maturity period, drain in case of rain, and let the rice field dry naturally. During the rest of the growth period, wet irrigation is used, and the water layer does not exceed 2 cm each time.

[0078] Method 3: Leave the field idle at the end of tillering, drain for 2 days, flood for 2 days, and then leave the field idle for 8 days, with a total of about 10 days of dry days; leave the field idle after the waxy maturity period, drain in case of rain, and let the rice field dry naturally. During the rest of the growth period, keep the water level no higher than 5 cm.

[0079] Method 4: Do not leave the field open at the end of tillering; leave the field open after the waxy stage, drain water when it rains, and let the paddy field dry naturally. During the entire growth period, keep the water layer at 5 to 10 cm when irrigating.

[0080] The specific implementation points of Method 1 are as follows:

[0081] Rest period 1: Rest the fields at the end of tillering, dry the fields for 2 days, flood the fields for 2 days, dry the fields again and rest the fields for 8 days, the total number of rest days is 10 days.

[0082] Field-leaving period 2: After the waxy stage, the fields are left dry, that is, no more water is poured after the filling is completed, and drainage is carried out when it rains to allow the rice fields to dry naturally.

[0083] Water management during the growing period: Lightly control water from the heading stage, and expose the fields frequently until the end of grain filling.

[0084] The specific implementation points of Method 2 are as follows:

[0085] Rest period 1: Rest the fields at the end of tillering, dry the fields for 2 days, flood the fields for 2 days, dry the fields again and rest the fields for 8 days, the total number of rest days is 10 days.

[0086] Field-leaving period 2: After the waxy stage, the fields are left dry, that is, no more water is poured after the filling is completed, and drainage is carried out when it rains to allow the rice fields to dry naturally.

[0087] Water management during the growing period: Carry out moist irrigation from the heading stage to the end of grain filling. The water layer should not exceed 2 cm each time and the field can be exposed appropriately.

[0088] The test results are as follows Figure 8 , because the open field in the growth process of method 1 is conducive to the growth of weeds, the weeds in the rice field are vigorous and not conducive to the growth of rice, even if it does not reduce the yield ( Fig. 9 ), but it is not conducive to farmers' management. Comparing method 1 with method 2, we can see that ( Figure 8 and Fig. 9 ), excessive water control to expose the field during the rice growth period will significantly reduce the mercury content in brown rice, but method 2 can already reduce it to below the national standard limit, the rice growth is good, and the paddy field is healthy.

[0089] In this implementation case, weeding was carried out twice during the rice growth cycle: conventional weeding was carried out 1 to 2 days before transplanting; the second conventional weeding was carried out after tillering, that is, on the 17th day after transplanting. It should be noted that the field should be properly dried when applying herbicides. During the technical implementation process, the herbicide can be added once when the field is left dry at the end of tillering, depending on the growth of the rice field, and it can be sprayed together with the pesticide for preventing diseases and insect pests.

[0090] The invention scheme has shown significant results after being implemented in rice fields growing Nanjing 46 in southern Jiangsu Province. It is mainly aimed at soils with mercury concentrations of 0.6 to 1.6 mg / kg, which can effectively reduce the mercury content in Nanjing 46 brown rice without significantly affecting the yield of this variety of rice. Compared with the method of continuous flooding irrigation throughout the growth period commonly used by farmers, the mercury content in brown rice decreased by 48.99% to 64.09%. After implementing this technical scheme in rice fields with mild to moderate mercury pollution in southern Jiangsu, the mercury content in brown rice can be effectively controlled to meet the national standard GB 2762-2022 "National Food Safety Standard Limits of Contaminants in Food" (mercury content in brown rice <20μg / kg).

[0091] The irrigation water in the above four examples has been tested by a testing unit with CMA qualification certification in accordance with HJ 597-2011 "Determination of Total Mercury in Water Quality by Cold Atomic Absorption Spectrophotometry", and all comply with GB 5084-2021 "Agricultural Irrigation Water Quality Standards" (total mercury ≤ 0.001 mg / L).

Claims

1. A method for reducing the mercury content of brown rice in rice fields with mild to moderate mercury pollution, characterized in that the steps include: 30 to 40 days after transplanting, start intermittent field lodgement at the end of the tillering stage. Regardless of whether there is rainfall or not, ensure that the total number of days of drying out reaches 10 days. The degree of field lodgement is determined by the presence of cracks in the fields, the sword-shaped rice leaves extending upward and being prickly to the touch. After the waxy stage, the fields are lodgement and irrigation is stopped to allow the rice fields to dry out naturally. Water control during the growing period: carry out moist irrigation from the heading stage to the end of filling, and the water layer should not exceed 2 cm each time.

2. The method for reducing the mercury content of brown rice in rice fields with mild to moderate mercury pollution according to claim 1, characterized in that: The lightly to moderately mercury-contaminated rice fields have a soil mercury concentration of 0.6 to 1.6 mg / kg.

3. The method for reducing the mercury content of brown rice in rice fields with mild to moderate mercury pollution according to claim 1, characterized in that: After the wax maturity period, the fields are left idle and drained when it rains.

4. The method for reducing the mercury content of brown rice in rice fields with mild to moderate mercury pollution according to claim 1, characterized in that: Water is controlled during the growth period and drainage is timely to prevent the water level in the rice field from exceeding 2 cm for a long time after rainfall.

5. The method for reducing the mercury content of brown rice in rice fields with mild to moderate mercury pollution according to claim 4, characterized in that: The rice varieties are Suxiangjing (Sujing) 1176, Chunyou 927, Ningxiangjing 9, Changxiangjing 1813, Xiushui 121 or Nanjing 46.

6. The method for reducing the mercury content of brown rice in rice fields with mild to moderate mercury pollution according to claim 1, characterized in that: The field-leaving method is applicable to the southern Jiangsu region.

7. The method for reducing the mercury content of brown rice in rice fields with mild to moderate mercury pollution according to claim 1, characterized in that: The rice is additionally applied with herbicide at least once after transplanting.

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