Foliar blocking and controlling agent for reducing cadmium absorption of rice grains as well as preparation method and application of foliar blocking and controlling agent

Abstract

The invention provides a leaf surface blocking and controlling agent for reducing cadmium absorption of rice grains as well as a preparation method and application of the leaf surface blocking and controlling agent, and belongs to the technical field of leaf surface fertilizers. The invention discloses a leaf surface blocking and controlling agent for effectively reducing cadmium accumulation of rice. The leaf surface blocking and controlling agent comprises the following effective components: potassium humate and a Zn < 2 + > solution. According to the invention, the potassium humate and a Zn < 2 + > solution are mixed to prepare a turbid liquid, namely the leaf surface resistance and control agent. The leaf surface blocking and controlling agent can be directly sprayed in the key period of rice growth, absorption of rice to zinc can be promoted, antioxidant enzyme activity of rice plants is improved, absorption of rice roots to cadmium and migration of cadmium in rice tissues are reduced, and therefore the content of Cd in rice is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of foliar fertilizers, and in particular relates to a foliar control agent for reducing cadmium absorption by rice grains, and a preparation method and application thereof. Background Art

[0002] As one of the most toxic heavy metal pollutants in the environment, cadmium (Cd) can accumulate in the food chain and cause various health risks such as renal dysfunction. Studies have shown that dietary intake has become the main route of cadmium exposure in humans, among which "cadmium rice" produced in cadmium-contaminated rice fields is particularly concerning.

[0003] Rice is the staple food source for half of the world's population. Its special physiological characteristics make it a cadmium hyperaccumulator. Currently, reducing the cadmium bioaccumulation coefficient of rice has become a research hotspot in the international agricultural environment field. Through comprehensive measures such as molecular breeding to improve rice absorption characteristics, developing soil passivation technology, and establishing a graded management system for contaminated farmland, a systematic solution to ensure food security and promote sustainable agricultural development is being formed. At present, the treatment technologies for cadmium pollution in farmland mainly include soil passivation, water management, and breeding of low-accumulation varieties, but there are problems such as high cost, complex operation, or unstable results. Summary of the invention

[0004] The invention provides a foliar barrier for reducing cadmium absorption in rice grains, a preparation method and application thereof. After use, the foliar barrier can significantly reduce the Cd content in the grains.

[0005] The invention provides a foliar control agent for reducing the cadmium content in rice grains, the raw materials of which are potassium humate and Zn 2+ Solution.

[0006] In a preferred embodiment of the present invention, the Zn 2+ Solutions include zinc sulfate solutions.

[0007] In a preferred embodiment of the present invention, in the potassium humate solution, the mass volume percentage of potassium humate is 1%;

[0008] The mass volume percentage of zinc sulfate in the zinc sulfate solution is 1%.

[0009] In a preferred embodiment of the present invention, the volume ratio of the potassium humate solution to the zinc sulfate solution is (1:3) to (3:1).

[0010] In a preferred embodiment of the present invention, the volume ratio of the potassium humate solution to the zinc sulfate solution is 1:1.

[0011] The present invention also provides a method for preparing the above-mentioned leaf surface barrier agent, comprising the following steps: dissolving potassium humate into a potassium humate solution, mixing the potassium humate solution with Zn2+ The solutions are mixed into a suspension to obtain the foliar control agent.

[0012] In a preferred embodiment of the present invention, the mixing is accompanied by stirring, the stirring speed is 200 rpm, and the time is 20 min.

[0013] The present invention also provides the application of the above-mentioned foliar control agent in reducing the cadmium content in rice grains.

[0014] The present invention also provides a method for reducing the cadmium content in rice grains, which includes spraying the above-mentioned foliar control agent once during each critical growth period of rice.

[0015] In a preferred embodiment of the present invention, the critical growth periods include the heading stage, the filling stage, and the maturity stage.

[0016] Beneficial effects: The present invention provides a foliar control agent prepared from Zn 2+ solution and potassium humate. The raw materials are few in type and wide in source. After the foliar control agent is used, it can take effect quickly. The foliar control agent of the present invention is a nanoparticle spraying agent prepared by loading Zn 2+ onto humic acid. Zinc, as a trace element required for rice growth and also a raw material for chlorophyll synthesis, zinc deficiency will cause leaf yellowing (especially new leaves) and brown spots. At the same time, zinc is also a cofactor or structural component of various antioxidant enzymes (such as POD, SOD, CAT, and APX, etc.). In particular, the synthesis of superoxide dismutase (SOD) that can scavenge reactive oxygen species requires the assistance of zinc, which can reduce the oxidative stress caused by cadmium (Cd) pollution. And there is a competitive relationship between zinc and cadmium. Supplementing zinc can reduce the absorption of cadmium by rice; humic acid can not only promote the root development of rice and enhance stress resistance, but also improve the absorption and utilization efficiency of nutrients by rice. Therefore, loading Zn 2+ onto humic acid particles can promote the absorption of zinc by rice under dual effects, improve the activity of antioxidant enzymes, and thus inhibit the accumulation of Cd in rice grains. In summary, the potassium humate and zinc (Zn 2+ ) have a synergistic effect on regulating the cadmium migration in rice. Description of the Drawings

[0017] Figure 1 shows the influence of humic acid-zinc foliar control agents with different mass ratios on the Cd accumulation in rice roots;

[0018] Figure 2 shows the influence of humic acid-zinc foliar control agents with different mass ratios on the Cd accumulation in rice stems;

[0019] Figure 3 shows the influence of humic acid-zinc foliar control agents with different mass ratios on the Cd accumulation in rice leaves;

[0020] Figure 4 Effect of humic acid-zinc foliar control agents with different mass ratios on Cd accumulation in rice grains;

[0021] Figure 5 Effect of humic acid-zinc foliar control agents with different mass ratios on Zn accumulation in rice stems;

[0022] Figure 6 Effect of humic acid-zinc foliar control agents with different mass ratios on Zn accumulation in rice leaves;

[0023] Figure 7 Effect of humic acid-zinc foliar control agents with different mass ratios on Zn accumulation in rice grains;

[0024] Figure 8 Effect of humic acid-zinc foliar control agents with different mass ratios on POD activity in rice stems;

[0025] Figure 9 Effect of humic acid-zinc foliar control agents with different mass ratios on SOD activity in rice stems;

[0026] Figure 10 Effect of humic acid-zinc foliar control agents with different mass ratios on CAT activity in rice stems;

[0027] Figure 11 Effect of humic acid-zinc foliar control agents with different mass ratios on APX activity in rice stems;

[0028] Figure 12 Effect of humic acid-zinc foliar control agents with different mass ratios on CAT activity in rice roots;

[0029] Figure 13 Effect of humic acid-zinc foliar control agents with different mass ratios on APX activity in rice roots;

[0030] Figure 14 SEM characterization result diagram of humic acid (HA);

[0031] Figure 15 SEM characterization result diagram of zinc sulfate (ZnSO4);

[0032] Figure 16 SEM characterization result diagram of humic acid-zinc (HA-Zn);

[0033] Figure 17 XPS full spectrum diagrams of humic acid (HA) and humic acid-zinc (HA-Zn). Specific implementation manners

[0034] The present invention provides a foliar control agent for reducing the cadmium content in rice grains, and the raw materials are potassium humate and Zn 2+Solution.

[0035] The potassium humate in the present invention exists in the form of a solution, and the mass-volume percentage content of potassium humate in the potassium humate solution is 1%. The Zn 2+ solution can be a zinc sulfate solution. In one embodiment, the mass-volume percentage content of zinc sulfate in the zinc sulfate solution is 1%. The mass ratio of the potassium humate solution to the zinc sulfate solution in the present invention can be (1:3) to (3:1). For example, in the examples, raw materials with mass ratios of 1:3, 1:1, and 3:1 were respectively constructed, and a foliar control agent was obtained after preparation. The potassium humate in the present invention can improve the fertilizer utilization rate and promote the growth of rice roots. Zinc can improve the resistance of rice to diseases such as rice blast and sheath blight. Preparing potassium humate and zinc sulfate into nanoparticles with Zn 2+ loaded onto humic acid can improve the activity of antioxidant enzymes, reduce the absorption of Cd by rice roots and the migration of Cd in rice tissues, and thus reduce the Cd content in rice grains.

[0036] The antioxidant enzymes referred to in the present invention include enzymes that have the ability to inhibit and scavenge reactive oxygen species generated during the plant growth process. For example, in the examples, the effects of the foliar control agent on the enzyme activities of peroxidase (POD), superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), etc. were identified. The antioxidant enzymes in the present invention can maintain the integrity of the root cell membrane by scavenging reactive oxygen species (ROS), reducing cadmium-induced membrane lipid peroxidation, and reducing the passive absorption of cadmium (such as the apoplastic pathway); the antioxidant enzymes maintain the integrity of the Casparian strip in the endodermis by reducing the damage of ROS to the cell wall, restricting the transport of cadmium to the above-ground part through the xylem, and achieving the limitation of xylem loading; the increase in antioxidant enzyme activity enables plants to tolerate higher concentrations of Cd and enhances the detoxification ability such as vacuolar compartmentalization, enabling other tissues of the plant except for the grains to store more Cd, thereby reducing the transport of Cd to the grains and improving the fixation ability of other tissues and cells outside the grains to Cd.

[0037] The present invention also provides a preparation method of the above-mentioned foliar control agent, including the following steps: dissolving potassium humate into a potassium humate solution, and mixing the potassium humate solution with Zn 2+ solution to form a suspension to obtain the foliar control agent.

[0038] During the mixing in the present invention, stirring is accompanied. The rotation speed of the stirring is 200 rpm and the time is 20 min. The temperature during the mixing is room temperature, such as 25 ± 3°C. In an embodiment of the present invention, a 1% (m / v) potassium humate (HA) solution and a 1% (m / v) zinc sulfate (ZnSO4) solution are respectively prepared; after the two solutions are mixed, magnetic stirring is required during the mixing process. The stirring time is required to be 20 min and the rotation speed is required to be 200 rpm. It is carried out at room temperature (25 ± 3°C). The prepared foliar control agent (humic acid-zinc) is in a suspension state and needs to be shaken well before use.

[0039] The present invention also provides a method for reducing the cadmium content in rice grains, including spraying the above foliar control agent once at each critical growth stage of rice.

[0040] In a preferred embodiment of the present invention, the critical growth stages include the heading stage, the filling stage, and the maturity stage. When the present invention performs the spraying, an environment with no wind and dryness should be maintained as much as possible. The front and back sides of the rice leaves are evenly sprayed, and small liquid beads should be formed on the leaf surface. Due to the strong effect of the foliar control agent, only 3 - 5 ml (stock solution) is required for each rice plant on average, and the spraying amount in the paddy field is 2 L of stock solution per mu. The foliar control agent of the present invention can improve the activity of antioxidant enzymes, reduce the absorption of Cd by rice roots and the migration of Cd in rice tissues, and thus reduce the Cd content in rice. At the same time, the raw materials of the control agent are all safe and harmless to rice crops and will not cause secondary pollution. It is a new type of environmentally friendly spraying agent.

[0041] To further illustrate the present invention, the following describes in detail a foliar control agent for reducing cadmium absorption in rice grains provided by the present invention, its preparation method and application in combination with embodiments, but they cannot be understood as limiting the protection scope of the present invention.

[0042] Application of the foliar control agent: Foliar spraying is carried out at the heading stage, the filling stage, and the maturity stage respectively. About 2 L of the humic acid-zinc stock solution is applied per mu for spraying. If the pollution is relatively serious, it can be increased to 4 - 4.5 L per mu.

[0043] Example 1

[0044] The foliar control agent (humic acid-zinc) is mainly a suspension prepared from potassium humate and zinc sulfate. The preparation process: Different proportions of potassium humate (HA) solution and zinc sulfate (ZnSO4) are fused. The specific ratios are shown in Table 1.

[0045] Table 1 Preparation ratios of humic acid-zinc nanoparticles with different dosing ratios

[0046] <![CDATA[Mass ratio of ZnSO4]]> Number Formulation ratio 0 Zn-HA0 HA (w / v, 1%) 100 mL 0.25 Zn-HA0.25 <![CDATA[ZnSO4 (w / v, 1%) 25 mL + HA (w / v, 1%) 75 mL]]> 0.5 Zn-HA0.5 <![CDATA[ZnSO4 (w / v, 1%) 50 mL + HA (w / v, 1%) 50 mL]]> 0.75 Zn-HA0.75 <![CDATA[ZnSO4 (w / v, 1%) 75 mL + HA (w / v, 1%) 25 mL <!-- 3 -->]]> 1 Zn-HA1 <![CDATA[ZnSO4 (w / v, 1%) 100 mL]]>

[0047] Rice pot experiments were carried out using humic acid-zinc foliar control agents with different application ratios: The rice pot experiments were conducted in a greenhouse with a constant temperature. The experimental soil was collected from farmland in the Nandan mining area of Guangxi. The rice variety selected was "Jingliangyou 534". When the rice seedlings were cultivated to the seedling stage (growing to 3 leaves and 1 heart), the experiment was carried out. The soil was pre-packed in plastic buckets and subjected to flooding treatment. A compound fertilizer of 1 g / kg soil was applied as the base fertilizer. 4 rice seedlings were planted in each pot of soil, divided into 5 treatment groups, and each treatment was repeated 3 times. The treatment groups were set as follows: (1) CK: control group; (2) Zn-HA0: spraying Zn-HA with a mass ratio of ZnSO4 of 0 (i.e., potassium humate); (3) Zn-HA0.25: spraying Zn-HA with a mass ratio of ZnSO4 of 0.25; (4) Zn-HA0.5: spraying Zn-HA with a mass ratio of ZnSO4 of 0.5; (5) Zn-HA 0.75: spraying Zn-HA with a mass ratio of ZnSO4 of 0.75; (6) Zn-HA 1: spraying Zn-HA with a mass ratio of ZnSO4 of 1 (i.e., ZnSO4).

[0048] Before spraying, the pH value of each solution was adjusted to 5.0 - 5.5 with 0.1 mol / L HCl or NaOH. The rice was sprayed once during the heading stage, filling stage, and maturity stage. The control group was sprayed with the same volume of clear water. When spraying, hold the sprayer and evenly spray the solution on the leaves to make both the front and back of all leaves completely wet without dripping. At the same time, cover a layer of tin foil above the soil to prevent the solution from spraying onto the soil.

[0049] Collection process: The whole rice plants at the maturity stage of each treatment were collected, the roots and rhizomes of the plants were washed clean with tap water, and then blanched in an oven at 105°C for 30 min, and then dried at 60°C for 72 h until constant weight for subsequent analysis.

[0050] Detection method:

[0051] Determination of cadmium content in rice plants: The dried rice plants were divided into 4 parts: roots, stems, leaves, and grains. After being cut into pieces with ceramic scissors, 0.3 g of the sample was taken into a polytetrafluoroethylene digestion tank, 8.7 mL of nitric acid and 1.3 mL of perchloric acid were added, and then left overnight. Then, digestion was carried out on an electric hot plate until the solution volume was less than 2 mL and the color was light yellow or colorless. Finally, it was made up to 25 mL with pure water and shaken well. After the solution passed through a 0.45 μm filter membrane, the cadmium element contents of the roots, stems, leaves, and grains were determined by inductively coupled plasma mass spectrometry (ICP-MS), and the zinc contents of the stems, leaves, and grains were determined.

[0052] Determination of antioxidant enzyme activity in rice: At the mature stage, 0.5 g of fresh leaf and root tissues were cut from each treatment group before collection, and then shredded with ceramic scissors. The POD activity, SOD activity, CAT activity, and APX activity were measured respectively. The activities of POD, SOD, CAT, and APX were all measured using the detection kits developed by Yishijiu (Lianyungang, Jiangsu) Biotechnology Co., Ltd., and the specific operation methods were carried out according to the corresponding kit instructions.

[0053] The transfer efficiency of cadmium among different tissues The transfer efficiency among tissues is expressed by the cadmium transfer factor (TF). TF is calculated according to Formulas I-IV:

[0054] TF 根-茎 = C 根 / C 茎 , Formula I;

[0055] TF 茎-叶 = C 茎 / C 叶 , Formula II;

[0056] TF 茎-籽粒 = C 茎 / C 籽粒 , Formula III;

[0057] TF 根-籽粒 = C 根 / C 籽粒 , Formula IV;

[0058] Among them, C 根 (mg / kg), C 茎 (mg / kg), C 叶 (mg / kg) and C 籽粒 (mg / kg) represent the cadmium contents in the roots, stems, leaves, and grains of rice respectively.

[0059] Data analysis:

[0060] The cadmium accumulation in rice roots is shown in Figure 1 . The cadmium contents of Zn-HA 0, Zn-HA 0.25, Zn-HA 0.5, and Zn-HA 1 were significantly lower than those of the CK, decreasing by 38.83%, 35.05%, 31.28%, and 56.63% respectively. This may be because the increase in root antioxidant enzymes inhibited Cd-induced membrane lipid peroxidation and reduced the passive absorption of cadmium by root cells. The cadmium accumulation in the stem is as shown in Figure 2As shown, the humic acid-zinc foliar control agent with each mass ratio has the effect of reducing cadmium accumulation in the stem. Zn-HA0, Zn-HA 0.25, Zn-HA 0.5, Zn-HA 0.75, and Zn-HA 1 reduced it by 54.1%, 63.12%, 66.14%, 44.91%, and 18.72% respectively compared with the blank group. Among them, Zn-HA 0.5 has the most significant effect on reducing cadmium accumulation in the stem. On the contrary, the humic acid-zinc foliar control agent enhanced the diversion of Cd to the leaves ( Figure 3 ). Compared with CK, Zn-HA0, Zn-HA 0.25, Zn-HA 0.5, Zn-HA 0.75, and Zn-HA 1 are 1.04 times, 1.18 times, 1.67 times, 2.64 times, and 2.76 times that of CK respectively. At the same time, referring to the transport efficiency of cadmium between plant tissues (Table 2), the TF 根-茎 of Zn-HA with each mass ratio was significantly lower than that of CK, and Zn-HA0.5 was the lowest treatment. And the TF 茎-叶 and TF 茎-籽粒 of each Zn-HA treatment group showed a consistent pattern, that is, TF 茎-叶 was higher than that of CK, while TF 茎-籽粒 was lower than that of CK, indicating that Zn-HA has the function of regulating cadmium transport, diverting the absorbed Cd to the leaves, and reducing Cd accumulation in the grains. Among them, the effect of Zn-HA 0.5 is the best.

[0061] Cadmium accumulation in the grains is shown in Figure 4 . Zn-HA 0, Zn-HA0.25, Zn-HA0.5, Zn-HA 0.75, and Zn-HA 1 reduced it by 13.82%, 73.08%, 72.32%, 58.41%, and 42.53% respectively compared with the blank group. That is, both Zn-HA 0.25 and Zn-HA 0.5 are ratios that can effectively reduce cadmium accumulation in rice grains. And the transport efficiency of cadmium between plant tissues (Table 2) also shows that Zn-HA 0.5 has the best inhibitory effect on the migration from roots to grains (TF 根-籽粒 ). In summary, the humic acid-zinc foliar control agent of Zn-HA0.5 is the best ratio for inhibiting rice from absorbing cadmium. It has a significant effect on reducing cadmium accumulation in rice grains and also has the ability to divert cadmium to the leaves.

[0062] Table 2 Transport efficiency of cadmium between plant tissues

[0063] Treatment group TF-(root-stem) TF-(stem-leaf) TF-(stem-grain) TF-(root-grain) CK 0.297 0.145 0.016 0.01238 Zn-HA0 0.349 0.19 0.0236 0.00573 Zn-HA0.25 0.266 0.275 0.0112 0.00304 Zn-HA0.5 0.181 0.408 0.0129 0.0024 Zn-HA0.75 0.299 0.395 0.0118 0.00353 Zn-HA1 0.876 0.279 0.0111 0.00972

[0064] The absorption effect of zinc by rice stems, leaves and grains after spraying is as shown in Figures 5 to 7As shown, the Zn contents of Zn-HA 0, Zn-HA 0.25, Zn-HA 0.5, Zn-HA 0.75, and Zn-HA 1 are all significantly higher than that of CK, and the roots, stems, and leaves all show a tendency to accumulate more zinc with the increase of the mass ratio of zinc sulfate. For example, the Zn accumulations in the roots of Zn-HA 0, Zn-HA 0.25, Zn-HA 0.5, Zn-HA 0.75, and Zn-HA 1 are 2.29 times, 2.21 times, 2.22 times, 4.19 times, and 7.42 times that of CK, respectively. However, the Cd concentrations in the stems and grains of Zn-HA 0.75 and Zn-HA 1 are significantly higher than those of Zn-HA 0.5, indicating that excessive zinc concentration will instead promote the absorption of Cd. The absorption of zinc by rice is concentration-dependent. With the increase of the zinc mass ratio, the zinc accumulations in the stems, leaves, and grains increase synchronously( Figures 5 to 7 ), indicating that rice has a strong ability to absorb zinc, and excessive application of zinc may affect the growth of rice.

[0065] After spraying the humic acid-zinc foliar control agent on rice, the changes in the activities of four antioxidant enzymes in the stems at the mature stage are as Figures 8 to 11 shown. The POD activities of Zn-HA 0, Zn-HA 0.25, Zn-HA 0.5, and Zn-HA 1 are significantly higher than that of CK( Figure 8 ), being 2.76 times, 1.97 times, 2.87 times, and 1.57 times that of CK, respectively, while the POD activity of Zn-HA 0.75 decreases compared with CK; compared with CK, only the SOD activities of Zn-HA 0.5 and Zn-HA 1 are significantly increased( Figure 9 ), and the other treatments all show a significant decrease; the CAT activities of Zn-HA 0.5 and Zn-HA 0.75 are significantly increased compared with CK( Figure 10 ), the CAT activities of Zn-HA 0 and Zn-HA 0.25 do not change much, and Zn-HA 1 even greatly inhibits the CAT activity; relative to CK, the APX activities at each concentration are generally increased( Figure 11 ), among which the APX activities of Zn-HA 0.5 and Zn-HA 0.75 are the highest, being 2.93 times and 3.16 times that of CK, respectively. To further understand the effect of enzyme activity on the absorption of Cd by roots, the CAT and APX activities in the roots are analyzed( Figure 12 and Figure 13 ). Among all treatments, only the CAT activities of Zn-HA 0, Zn-HA 0.25, Zn-HA 0.5, and Zn-HA 1 are significantly increased compared with CK( Figure 12 ), while in the comparison of APX activities, Zn-HA 0.5 is the only treatment that significantly increases the APX activity (compared with CK)( Figure 13 ).

[0066] In summary, the humic acid-zinc foliar inhibitor with a mass ratio of 0.5 is the best ratio for inhibiting rice from absorbing cadmium. It has a general promoting effect on the activity of antioxidant enzymes in stems and leaves, and inhibits the accumulation of Cd in roots, stems and grains of rice. Its mechanism of action has three main parts: (1) Oxidative cross-linking. Superoxide dismutase (SOD) can convert O 2- It is converted into H2O2, thereby promoting oxidative cross-linking in the cell wall. Oxidative cross-linking is an oxidation reaction mediated by active oxygen (such as H2O2), which can form covalent bonds between biological macromolecules (such as proteins, polysaccharides or phenolic compounds), thereby strengthening the rigidity and density of the cell wall and reducing cadmium penetration. Oxidative cross-linking also increases the negative charge density of the cell wall (such as the carboxyl groups generated by pectin demethylation), and fixes Cd through ion exchange adsorption. 2+ , inhibiting the transfer of Cd between rice tissues, which is consistent with the results that humic acid-zinc reduces the transfer factor of Cd and increases the activity of SOD in stems and roots. (2) CAT and APX can reduce the absorption of Cd by inhibiting the membrane lipid peroxidation of root cells. CAT mainly removes H2O2 in peroxisomes, while APX depends on the ascorbic acid-glutathione cycle to play a role in the cytoplasm and chloroplasts. The two enzymes can synergistically reduce the membrane lipid peroxidation damage of H2O2 to cell membranes induced by cadmium, maintain the integrity of root cell membranes, and reduce the passive absorption of cadmium. After spraying Zn-HA 0.5, the significant increase in the activity of root CAT and APX and the significant decrease in the Cd content in the roots verified this process. (3) Antioxidant enzymes can maintain the integrity of the Casparian strip by reducing ROS (reactive oxygen species), thereby inhibiting Cd migration. Casparian strips can force Cd to enter the xylem through the symplasmic pathway of endodermal cells instead of directly through the apoplast, thus limiting the migration pathway of Cd. In addition, the cell walls of the outer cells of the endodermis will be blocked by pectin carboxyl groups (-COO - ) and lignin phenolic hydroxyl (-OH) adsorb Cd, strengthening the fixation of Cd by cells. However, the invasion of Cd will induce the outbreak of ROS, destroy the integrity of the Caspian strip, and promote the rapid absorption of Cd, while the increase in the activity of antioxidant enzymes (such as SOD) can inhibit this effect, that is, the application of humic acid-zinc limits the behavior of Cd accelerating transport and migration by destroying plant tissue structure. In addition, the Zn content input to rice by Zn-HA 0.5 is relatively moderate, which will neither affect the barrier effect of Cd nor cause excessive accumulation of Zn in the grains to affect rice growth.

[0067] Example 2

[0068] The specific configuration process of the optimal ratio (1:1) foliar control agent (humic acid-zinc):

[0069] (1) Prepare a 1% (m / v) potassium humate (HA) solution and a 1% (m / v) zinc sulfate (ZnSO4) solution respectively. 1% (m / v) means 10 g of the substance is dissolved in 1 L of water.

[0070] (2) Mix the two in a 1:1 ratio.

[0071] (3) During the mixing process, magnetic stirring is required. The stirring time is 20 min and the rotation speed is 200 rpm. It is carried out at room temperature (25 ± 3 °C).

[0072] (4) The prepared foliar control agent (humic acid - zinc) is in a suspension state and needs to be shaken well before use.

[0073] Example 3

[0074] Preparation of materials: Stir and mix 50 ml of potassium humate (w / v, 1%) and 50 ml of zinc sulfate (w / v, 1%) in a 1:1 ratio to prepare a humic acid - zinc foliar control agent with a mass ratio of 0.5.

[0075] To show that zinc particles have been successfully loaded onto humic acid, dehydrate the humic acid - zinc foliar control agent prepared according to the ratio. First, separate the liquid phase and solid phase of the humic acid - zinc foliar control agent by a high - speed centrifuge (4000 r / min) to obtain humic acid - zinc nanoparticles, and then use a vacuum freeze - dryer to dry the nanoparticles and store them in a drying dish for characterization.

[0076] To observe the loading of zinc particles on humic acid, perform SEM and XPS characterizations on humic acid zinc sulfate and humic acid - zinc nanoparticles respectively.

[0077] SEM uses a Merlin field - emission scanning electron microscope (ZEISS, Germany) to characterize the morphologies of the prepared humic acid - zinc, humic acid (HA), and zinc sulfate (ZnSO4). After sputtering with gold, place the prepared samples in the SEM to observe the morphologies ( Figures 14 to 16 ).

[0078] XPS uses a Thermo ESCALAB - 250 with monochromatic Al Ka radiation to detect the surface elements and chemical compositions of humic acid - zinc and humic acid (HA) ( Figure 17 ).

[0079] As shown by the SEM images of humic acid (HA), zinc sulfate (ZnSO4), and zinc humate (HA-Zn), the surface morphology of humic acid is relatively smooth and fluffy, making it easier to be absorbed by leaves. It can also promote the root development of rice, increase the tiller number and leaf area, delay leaf senescence, and ultimately increase the yield. However, its ability to control Cd migration is limited. The morphology of zinc sulfate is mainly an inorganic salt crystal structure (such as blocky, needle-like, or flaky). The surface of rice leaves is covered with a waxy layer and cutin layer, which is smooth and hydrophobic. Coarse zinc sulfate particles are likely to slide off the leaf surface or only loosely adhere, making it difficult to enter the leaf interior through stomata or cutin layer cracks. Humic acid-zinc makes up for the shortcomings of both. After loading and fusion, fragmented zinc sulfate particles are basically filled and embedded into the pores and surface depressions of humic acid, forming relatively smooth and round nanoparticles. This not only protects zinc ions from binding and inactivation with phosphates, carbonates, etc. in the soil or leaf surface (such as zinc sulfate being easily antagonistic to phosphorus), but also improves the foliar absorption rate of zinc. At the same time, humic acid itself can penetrate through leaf stomata and the cutin layer, carrying zinc ions into the plant body, which is more efficient than the passive absorption of single zinc sulfate. The full XPS spectra of humic acid (HA) and zinc humate (HA-Zn) are as Figure 17 shown. The Zn2p peak of zinc humate is significantly higher than that of humic acid, indicating that zinc elements have been successfully loaded onto the surface of humic acid particles, and zinc humate indeed has the function of carrying zinc for migration.

[0080] Although the above embodiments have described the present invention in detail, they are only a part of the embodiments of the present invention, not all of them. People can also obtain other embodiments based on these embodiments without creative efforts, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A foliar control agent for reducing the cadmium content in rice grains, characterized in that: The raw materials are potassium humate and Zn 2+ Solution.

2. The leaf surface control agent according to claim 1, characterized in that: The Zn 2+ Solutions include zinc sulfate solutions.

3. The leaf surface control agent according to claim 2, characterized in that: In the potassium humate solution, the mass volume percentage of potassium humate is 1%; The mass volume percentage of zinc sulfate in the zinc sulfate solution is 1%.

4. The leaf surface control agent according to claim 3, characterized in that: The volume ratio of the potassium humate solution to the zinc sulfate solution is (1:3) to (3:1).

5. The leaf surface control agent according to claim 3 or 4, characterized in that: The volume ratio of the potassium humate solution to the zinc sulfate solution is 1:

1.

6. The method for preparing the leaf surface control agent according to any one of claims 1 to 5, characterized in that: The following steps are involved: Dissolve potassium humate into a potassium humate solution, and mix the potassium humate solution with Zn 2+ The solutions are mixed into a suspension to obtain the foliar barrier control agent.

7. The preparation method according to claim 6, characterized in that: The mixing was accompanied by stirring at a rotation speed of 200 rpm for 20 minutes.

8. Use of the foliar barrier agent according to any one of claims 1 to 5 in reducing the cadmium content in rice grains.

9. A method for reducing the cadmium content in rice grains, characterized in that: The method comprises spraying the foliar barrier agent according to any one of claims 1 to 5 once at each critical period of rice growth.

10. The method according to claim 9, characterized in that: The key periods include heading stage, grain filling stage and maturity stage.

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