Rice cadmium-reducing and selenium-enriching slow-release compound agent, preparation method and application thereof

Abstract

The application relates to the technical field of rice planting, and discloses a rice cadmium-reducing and selenium-enriching slow-release compound agent as well as a preparation method and application thereof. The rice cadmium-reducing and selenium-enriching slow-release compound agent is prepared by ball milling zero-valent iron and hydroxyapatite and then compounding the ball-milled product with a calcium selenite solution. The compound agent is used in the process of rice planting to obtain rice with low cadmium content and high selenium content. The sand culture and pot culture test results of the application show that, after the application of the rice cadmium-reducing and selenium-enriching slow-release compound agent, the cadmium reduction rate of the rice can reach 61.6%, and the selenium content of the rice can increase by 302%. In conclusion, the application can reduce the cadmium content in rice by a relatively simple process, and the effect of the application on the rice field can be maintained for a long time. In addition, the application also solves the problem of excessively high selenium content of rice after the treatment of a selenium-containing improving agent, and the selenium content of rice treated by the slow-release compound agent is reduced by 54.48% compared with the selenium content of rice treated by the selenium improving agent alone.

Description

Technical Field

[0001] This invention relates to the field of rice cultivation technology, and in particular to a slow-release compound agent for reducing cadmium and enriching selenium in rice, its preparation method, and its application. Background Technology

[0002] Cadmium is not an essential nutrient for rice growth, but in cadmium-contaminated farmland, rice plants absorb cadmium through their roots, leading to its accumulation in large quantities. As rice is a major food crop in southern my country, rice consumption is the primary route of cadmium exposure for local residents. Cadmium accumulates through the food chain, eventually building up in the human body and causing disease, posing a serious threat to the ecological environment, agricultural product quality and safety, and human health. According to the latest national soil survey report, cadmium is a major pollutant in paddy fields, and cadmium levels in rice are frequently exceeding standards. Therefore, reducing cadmium content in rice and ensuring food security is a pressing problem that my country urgently needs to solve.

[0003] The absorption of cadmium by rice is closely related to the iron metabolism pathway. Spraying iron fertilizer can improve the amount and rate of iron absorption in rice, thereby increasing cadmium transport competition and reducing the cadmium content in rice grains. Rice exhibits significant differences in the absorption and utilization rates of iron with different valence states. Studies have reported that rice has a strong absorption capacity for ferrous iron (Fe2+), but most iron fertilizers on the market have poor water solubility and stability, easily converting to ferric iron (Fe3+) during application, thus reducing their absorption and utilization rate. Chinese invention patent 200710070666.4 discloses a method for controlling the accumulation of the heavy metal cadmium in rice. This method involves applying ferrous chelates to the soil at different growth stages of rice to reduce the cadmium content in rice. However, the application of ferrous chelates alters the original soil properties and structure, and the dosage is relatively large, resulting in high costs.

[0004] Selenium is an important trace element; it is beneficial to organisms at low concentrations, but exhibits toxicity similar to heavy metals at high concentrations. Rice can absorb SeO4 through the Si absorption transporter Lsi1. 2- It enters the root system, and SeO3 2- It can be absorbed by the roots via the phosphate transporter OsPT2. Studies have found that applying selenium-containing amendments can effectively reduce the accumulation of Cd in the aboveground parts of rice. However, to date, the method of using selenium-containing amendments to reduce stunting in rice still has some problems: First, most of the currently used selenium-containing amendments are easily soluble in water, have poor residual effect, and require annual spraying, which consumes a lot of manpower and resources, resulting in high costs; second, the selenium content in rice treated with selenium-containing amendments is often too high, which has adverse effects on human health. In the specific treatment process, it is also necessary to pay attention to controlling the selenium content of rice.

[0005] Studies have reported that iron and selenium can mutually promote absorption under certain conditions, and that phosphate and selenite compete for absorption. Considering that there are currently no reports on the application of iron-phosphate amendments combined with selenium-containing amendments in the absorption and accumulation of cadmium in rice, it is necessary to provide a slow-release compound for reducing cadmium in rice, its preparation method, application, and treatment method to solve or at least alleviate the problems of high cost, poor long-term cadmium-reducing effect, and excessively high selenium content in rice after treatment. Summary of the Invention

[0006] The main objective of this invention is to provide a slow-release compound agent for reducing cadmium and enriching selenium in rice, its preparation method, and its application method, aiming to solve the technical problems of high cost, poor long-term effect of reducing cadmium, and excessive selenium content in rice after treatment in the prior art.

[0007] To achieve the above objectives, the present invention provides a method for preparing a slow-release compound agent for reducing cadmium and enriching selenium in rice, as follows: the slow-release compound agent is obtained by compounding a slow-release iron-phosphorus composite material and a calcium selenite suspension, wherein the mass ratio of the slow-release iron-phosphorus composite material to calcium selenite is 1:0.01-0.05, preferably 1:0.03; the slow-release iron-phosphorus composite material is obtained by solid-phase ball milling zero-valent iron powder and hydroxyapatite, wherein the mass ratio of zero-valent iron powder to hydroxyapatite is 1:0.2-0.8; preferably, the mass ratio of zero-valent iron powder to hydroxyapatite is 1:0.6-0.7, and more preferably 1:0.66.

[0008] Further, the selenite solution is mixed with the calcium hydroxide suspension to obtain the calcium selenite suspension.

[0009] Further, the solid content of the calcium selenite suspension is 0.05-0.15 g / L, preferably 0.1 g / L; the solid-liquid ratio of the slow-release iron-phosphorus composite material and the calcium selenite suspension is 1:200-400 g / mL; preferably, the solid-liquid ratio of the slow-release iron-phosphorus composite material and the calcium selenite suspension is 1:300-350 g / mL; more preferably 1:320 g / mL.

[0010] Furthermore, in preparing the calcium selenite suspension, the mass ratio of Se to Ca added to the system is 1:0.5-1.5, preferably 1:0.7-0.75, and more preferably 1:0.72.

[0011] Furthermore, the slow-release iron-phosphorus composite material is made by solid-phase ball milling of zero-valent iron powder and hydroxyapatite, followed by sieving through a 100-mesh sieve.

[0012] The present invention also provides a slow-release compound agent for reducing cadmium and enriching selenium in rice, which is prepared using the preparation method described above.

[0013] The present invention also provides the application of the aforementioned slow-release compound agent for reducing cadmium and increasing selenium in rice, for reducing cadmium content and increasing selenium content in rice.

[0014] Furthermore, the application includes applying the rice cadmium-reducing and selenium-enriching slow-release compound to the soil of the planting area before rice is planted.

[0015] Furthermore, when the rice cadmium-reducing slow-release compound is applied to the soil, the application ratio of the active ingredient iron-phosphorus composite material in the rice cadmium-reducing and arsenic-reducing slow-release compound is 5-15 kg / mu, and the application ratio of the active ingredient calcium selenite is 80-320 g / mu.

[0016] Furthermore, the soil was tilled both before and after applying the rice cadmium-reducing and selenium-enriched slow-release compound agent to the soil.

[0017] Furthermore, the soil should be kept level after tilling before applying the rice cadmium-reducing and selenium-enriched slow-release compound to the soil.

[0018] Furthermore, as a more reasonable application method, when applying the rice cadmium-reducing and selenium-enriching slow-release compound agent to the soil, the active ingredients in the agent are iron-phosphorus composite material and calcium selenite. Of course, depending on the adjustment of the selenium-calcium ratio, the active ingredients may also include substances such as calcium hydroxide. It should be noted that the rice cadmium-reducing and selenium-enriching slow-release compound agent generally exists in suspension form, with its active ingredients dispersed in the liquid and sprayed into the paddy field along with the liquid.

[0019] Compared with the prior art, the present invention has the following advantages:

[0020] 1. This invention can obtain a slow-release compound agent for reducing cadmium and enriching selenium in rice by simple solution mixing and mechanical ball milling. After being applied to the rice planting process, the slow-release compound agent can significantly reduce the accumulation of cadmium in rice, thus ensuring the dietary health of residents.

[0021] 2. In addition to the sustained-release and long-lasting cadmium-reducing effect of the iron-phosphorus composite material in the rice-based cadmium-reducing and selenium-enriched slow-release compound, the active ingredient in this invention is calcium selenite, with a Ksp = 10. -6.65 It can also be slowly released into the soil, meaning that once applied to the soil, it can remain stably in the soil for a long time, working synergistically with iron-phosphorus composite materials to maintain the long-term effect of reducing cadmium; and it can also be applied to the soil simultaneously with fertilizer, saving a lot of human resources costs.

[0022] 3. The preparation process of the rice cadmium-reducing and selenium-enriched slow-release compound agent of the present invention is simple, and the materials are widely available; it can be produced on a large scale industrially. The cost of spraying the rice cadmium-reducing and selenium-enriched slow-release compound agent is only 30-60 yuan / mu, which is 60% of the cost of foliar spraying barrier agents and 1.35% of the cost of applying iron-phosphorus soil passivating agents.

[0023] 4. The slow-release compound for reducing cadmium in rice in this invention can not only reduce cadmium, but also reasonably increase the selenium content in rice, so that the selenium content in rice is increased compared with ordinary rice, but not too high, resulting in selenium-enriched rice that is beneficial to the human body. Attached Figure Description

[0024] Figure 1 Example 1: The iron-phosphorus composite material of the present invention and zero-valent iron in soil Fe 2+ The release comparison;

[0025] Figure 2 This is a comparison chart of the selenium and cadmium content in rice in Example 2 and Comparative Example 2;

[0026] Figure 3 This is a comparison chart of cadmium content data in rice from Example 3 and Comparative Example 3;

[0027] Figure 4 This is a comparison chart of the selenium content in rice in Example 3 and Comparative Example 3. Detailed Implementation

[0028] The following examples are intended to further illustrate the present invention, but not to limit it.

[0029] Example 1

[0030] This embodiment uses soil from cadmium-contaminated farmland in Changsha County, Changsha City, Hunan Province for soil culture experiments. 100g of naturally dried soil was placed in a 500mL glass bottle. Three groups of experiments were conducted, with three replicates per group, designated CK, zero-valent iron, and an iron-phosphorus composite material. The specific steps are as follows:

[0031] (1) 3g of zero-valent iron powder and 2g of hydroxyapatite were placed in a ball mill jar, and ball milling balls with a ball-to-material ratio of 10:1 were added. After solid-phase ball milling at room temperature (25℃) and rotation speed (400r / min) for 2 hours, the slow-release iron-phosphorus composite material was obtained.

[0032] (2) Add the materials at a ratio of 0.01% of the soil mass and mix thoroughly. Then add deionized water at a ratio of 1:2 of the soil mass and mix again.

[0033] (3) After reactions of 2, 4, 7, 15 and 21 days, 5 mL of the reacted soil solution was taken, filtered, and the Fe in the filtrate was determined by o-non-porphyrin spectrophotometry. 2+content.

[0034] (4) Testing revealed that in this embodiment, the Fe in the soil solution differed from that in the zero-valent iron powder and CK treatments. 2+ The soil solution with Fe first rise and then fall, and the addition of iron-phosphorus composite material. 2+ The release of Fe showed a gradual upward trend, significantly better than zero-valent iron powder, and the Fe in the system 2+ The content has been significantly increased; see details below. Figure 1 .

[0035] Example 2

[0036] This embodiment uses late-season rice varieties collected from Changsha County, Changsha City, Hunan Province for sand culture experiments. 2 kg of naturally dried quartz sand was placed in a 10 L rhizosphere chamber. Two groups of experiments were conducted, with three replicates in each group, designated CK and Se+ material. The CK group had 0 mg / L of calcium selenite and the iron-phosphorus composite material, while the material group had 0.5 mg / L of selenium and 0.066 g / L of the iron-phosphorus composite material. The specific steps are as follows:

[0037] (1) Take 0.96 mL of 10000 mg / L cadmium stock solution, and dissolve 60.48 g of Hogland nutrient solution and 45.36 g of calcium nitrate in an appropriate amount of deionized water. Make up the volume to 48 L to obtain 0.2 mg / L cadmium-containing Hogland nutrient solution. Add 8 L to each root box.

[0038] (2) Dissolve 140.5 mg SeO2 in 1 L of water to obtain a selenite solution with a Se concentration of 100 mg / L. Dissolve 100 mg CaO in 1 L of water to obtain a calcium hydroxide suspension with a Ca concentration of 72 mg / L.

[0039] (3) Place 3g of zero-valent iron powder and 2g of hydroxyapatite in a ball mill jar, and add ball milling balls with a ball-to-material ratio of 10:1. After solid-phase ball milling at room temperature (25℃) and rotation speed (400r / min) for 2 hours, the slow-release iron-phosphorus composite material is obtained.

[0040] (4) Take a certain amount of selenite solution according to the ratio, and add a certain amount of calcium hydroxide suspension. After reacting for 15 minutes, a calcium selenite suspension is obtained. Then, mix the calcium selenite suspension with the iron-phosphorus composite material and add it to the rhizosphere chamber. The specific ratio is shown in the table below:

[0041]

[0042] (5) After the rice matures, the cadmium and selenium content in the rice is determined.

[0043] (6) Testing showed that in this embodiment, after applying the rice cadmium-reducing slow-release compound agent, the cadmium content in the rice was effectively reduced, and the selenium content was significantly increased. See details below. Figure 2 The comparison between the control group and the material group showed that the cadmium content in rice could be reduced from 5.55 mg / kg to 2.13 mg / kg, a decrease of 61.6%; while the selenium content could be increased from 0.48 mg / kg to 1.93 mg / kg, an increase of 302%.

[0044] Comparative Example 2

[0045] This embodiment uses a late-season rice variety from Changsha County, Changsha City, Hunan Province for sand culture experiments. 2 kg of naturally dried quartz sand was placed in a 10 L rhizosphere chamber. Two groups of experiments were conducted, with three replicates in each group: the Se group and the CK group (same as the CK group in Example 1). The specific steps are as follows:

[0046] (1) Take 0.96 mL of 10000 mg / L cadmium stock solution, and dissolve 60.48 g of Hogland nutrient solution and 45.36 g of calcium nitrate in an appropriate amount of deionized water. Make up the volume to 48 L to obtain 0.2 mg / L cadmium-containing Hogland nutrient solution. Add 8 L to each root box.

[0047] (2) Dissolve 140.5 mg SeO2 in 1 L of water to obtain a selenite solution with a Se concentration of 100 mg / L. Dissolve 100 mg CaO in 1 L of water to obtain a calcium hydroxide suspension with a Ca concentration of 72 mg / L.

[0048] (3) Dilute a certain amount of selenite solution according to the specified ratio, and add a certain amount of calcium hydroxide suspension. After reacting for 15 minutes, obtain calcium selenite suspension, and then add it to each rhizosphere chamber. See the table below for specific proportions:

[0049]

[0050] (4) After the rice matures, the cadmium and selenium content in the rice is determined.

[0051] (5)Reference Figure 1 As shown, the tests revealed the following: 1. In this comparative example, adding calcium selenite alone had no significant effect on reducing cadmium in rice; 2. Calcium selenite reduced the cadmium content in rice and increased the selenium content; 3. In Example 1, the selenium + material group, compared to the Se group, further reduced the Cd content in rice and slightly reduced the selenium content. This indicates that the slow-release compound for reducing cadmium in rice has a better cadmium-reducing effect than calcium selenite and can effectively control the selenium content.

[0052] Example 3

[0053] This embodiment uses cadmium-contaminated paddy soil collected from Shangxin Group, Yonghe Town, Liuyang City, Hunan Province for a pot experiment. 5 kg of naturally dried soil was placed in pots, with a total of 4 experimental groups, each with 3 replicates, numbered CK, 5 kg, 10 kg, and 15 kg. The CK group had a slow-release compound additive dosage of 0 mg / kg; the 5 kg group had an iron-phosphorus composite material dosage of 5 kg / mu and a selenium dosage of 0.5 mg / kg; the 10 kg group had an iron-phosphorus composite material dosage of 10 kg / mu and a selenium dosage of 0.5 mg / kg; and the 15 kg group had an iron-phosphorus composite material dosage of 15 kg / mu and a selenium dosage of 0.5 mg / kg. The specific steps are as follows:

[0054] (1) Dissolve 140.5 mg SeO2 in 1 L of water to obtain a selenite solution with a Se concentration of 100 mg / L. Dissolve 100 mg CaO in 1 L of water to obtain a calcium hydroxide suspension with a Ca concentration of 72 mg / L.

[0055] (2) Place 3g of zero-valent iron powder and 2g of hydroxyapatite in a ball mill jar, and add ball milling balls with a ball-to-material ratio of 10:1. After solid-phase ball milling at room temperature (25℃) and a rotation speed of 400r / min for 2 hours, the slow-release iron-phosphorus composite material is obtained.

[0056] (3) Take a certain amount of selenite solution according to the ratio, and add a certain amount of calcium hydroxide suspension. After reacting for 15 minutes, a calcium selenite suspension is obtained. Then, mix the calcium selenite suspension with the iron-phosphorus composite material and spray it onto the potting soil. The specific ratio is shown in the table below:

[0057]

[0058] (4) After the rice matures, the cadmium and selenium content in the rice is determined.

[0059] (5) Testing showed that in this embodiment, after applying the rice cadmium-reducing slow-release compound agent, the cadmium content in the rice was effectively reduced, and the selenium content was effectively increased. For details, please refer to [link to relevant documentation]. Figure 3 , Figure 4 The comparison between the 5kg group and the control group showed that: 1. The cadmium content in rice could be reduced from 0.52 mg / kg to 0.25 mg / kg, a decrease of 52%; 2. The selenium content in rice could be increased from 0.98 mg / kg to 1.34 mg / kg, an increase of 37%.

[0060] Comparative Example 3

[0061] This embodiment uses cadmium-contaminated paddy soil collected from Shangxin Group, Yonghe Town, Liuyang City for pot experiments. 5 kg of naturally dried soil was placed in pots, and three groups were conducted, with three replicates in each group: the calcium selenite group, the iron-phosphorus composite material group, and the control group (same as the control group in Example 2). The specific steps are as follows:

[0062] (1) 3g of zero-valent iron powder and 2g of hydroxyapatite were placed in a ball mill jar, and ball milling balls with a ball-to-material ratio of 10:1 were added. After solid-phase ball milling at room temperature (25℃) and rotation speed (400r / min) for 2 hours, the slow-release iron-phosphorus composite material was obtained.

[0063] (2) Dissolve 140.5 mg SeO2 in 1 L of water to obtain a selenite solution with a Se concentration of 100 mg / L. Dissolve 100 mg CaO in 1 L of water to obtain a calcium hydroxide suspension with a Ca concentration of 72 mg / L.

[0064] (3) Calcium selenite group: Take 25 mL of selenite solution and 28.33 mL of calcium hydroxide suspension and react for 15 min, then dilute to 100 mL and spray into the potting soil; Iron-phosphorus composite material group: Take 0.333 g of iron-phosphorus composite material to prepare 100 ml of suspension and spray into the potting soil.

[0065] (4) After the rice matures, the cadmium and selenium content in the rice is determined.

[0066] (5)Reference Figure 3 , Figure 4 As shown, the tests revealed the following: 1. In this comparative example, the iron-phosphorus composite material had no significant effect on reducing cadmium in rice; 2. Calcium selenite reduced the cadmium content in rice by 15%; 3. In Example 2, the 5kg group with the same amount of selenium addition, compared to the calcium selenite group, further reduced the Cd content in rice and decreased the selenium content from 1.61 mg / kg to 1.34 mg / kg. This indicates that there is a synergistic effect between the active ingredient calcium selenite in the rice cadmium-reducing slow-release compound and the iron-phosphorus composite material, resulting in a better cadmium-reducing effect and effective control of selenium content.

[0067] The above technical solutions of the present invention are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. All equivalent structural transformations made under the technical concept of the present invention using the contents of the present invention specification and drawings, or direct / indirect applications in other related technical fields, are included in the patent protection scope of the present invention.

Claims

1. A method for preparing a slow-release compound agent for reducing cadmium and enriching selenium in rice, characterized in that, The slow-release compound is obtained by compounding a slow-release iron-phosphorus composite material and a calcium selenite suspension, wherein the mass ratio of the slow-release iron-phosphorus composite material to calcium selenite is 1:0.01-0.05; the slow-release iron-phosphorus composite material is obtained by taking zero-valent iron powder and hydroxyapatite after solid-phase ball milling, wherein the mass ratio of zero-valent iron powder to hydroxyapatite is 1:0.2-0.

8.

2. The preparation method according to claim 1, characterized in that, The calcium selenite suspension is obtained by mixing the selenite solution with the calcium hydroxide suspension.

3. The preparation method according to claim 1, characterized in that, The solid content of the calcium selenite suspension is 0.05-0.15 g / L; the solid-liquid ratio of the slow-release iron-phosphorus composite material and the calcium selenite suspension is 1:200-400 g / mL.

4. The preparation method according to claim 1, characterized in that, When preparing calcium selenite suspension, the mass ratio of Se to Ca added to the system is 1:0.5-1.

5.

5. The preparation method according to claim 1, characterized in that, The slow-release iron-phosphorus composite material is made by solid-phase ball milling of zero-valent iron powder and hydroxyapatite, followed by sieving through a 100-mesh sieve.

6. A slow-release compound agent for reducing cadmium and enriching selenium in rice, characterized in that, It is prepared using the preparation method described in any one of claims 1-5.

7. The application of the rice cadmium-reducing and selenium-enriched slow-release compound agent according to claim 6, characterized in that, It is used to reduce the cadmium content and increase the selenium content in rice.

8. The application according to claim 7, characterized in that, include: Before transplanting rice, apply the rice cadmium-reducing and selenium-enriching slow-release compound agent as described in claim 6 to the soil in the transplanting area.

9. The application according to claim 8, characterized in that, When applying the rice cadmium-reducing and selenium-enriched slow-release compound agent to the soil, the application ratio of the active ingredient iron-phosphorus composite material in the rice cadmium-reducing and selenium-enriched slow-release compound agent is 5-15 kg / mu, and the application ratio of the active ingredient calcium selenite is 80-320 g / mu.

10. The application according to claim 8, characterized in that, Before and after applying the rice cadmium-reducing and selenium-enriched slow-release compound agent, the soil was tilled; before applying the rice cadmium-reducing and selenium-enriched slow-release compound agent to the soil, the tilled soil was kept level.

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