Biomass charcoal composite hydrogel slow-release fertilizer and preparation method and application thereof

Abstract

This invention discloses a biochar composite hydrogel slow-release fertilizer, its preparation method, and its application, belonging to the field of composite hydrogels and fertilizer preparation. The invention provides a biochar composite hydrogel slow-release fertilizer comprising biochar, hydrogel fixed in the pores and surface of the biochar, and elemental fertilizer mixed within the hydrogel. The hydrogel is prepared from metal cations and alginate. This invention proposes an "in-situ gelation within the pores" strategy, preparing the hydrogel in situ within the biochar pores to produce the biochar composite hydrogel slow-release fertilizer. This slow-release fertilizer exhibits high bonding strength between the biochar and hydrogel, high mechanical strength, and possesses both slow-release fertilizer function and soil-improving ability.

Description

Technical Field

[0001] This invention belongs to the field of composite hydrogels and fertilizer preparation, specifically relating to a biochar composite hydrogel slow-release fertilizer, its preparation method, and its application. Background Technology

[0002] Traditional slow-release fertilizers can delay nutrient release through coating or chemical modification, but processes such as sulfur coating and polymer coating make slow-release fertilizers 3-5 times more expensive than ordinary fertilizers, and they lack soil improvement capabilities.

[0003] Biochar can be prepared into biochar fertilizer, which can improve soil water retention and cation exchange capacity (CEC), and can also sequester carbon and reduce emissions, adsorbing heavy metals and organic pollutants. However, biochar itself has a low nutrient content, with N / P / K <3%, limiting its effectiveness as a direct fertilizer and requiring supplementation from external sources. Existing modification methods, such as those using physical adsorption or simple loading of nutrients (e.g., inorganic salts), have weak binding affinity to biochar, making them prone to leaching by rainwater or irrigation, resulting in short release periods and easy nutrient loss. Alternatively, they lack precise control mechanisms, leading to a sharp increase in nutrient release rates under high temperature or high humidity conditions, followed by stagnation at low temperatures, failing to match the needs of crop growth cycles and resulting in uncontrollable release.

[0004] Hydrogels (such as alginate and cellulose derivatives) can lock in water and nutrients through a three-dimensional network structure and achieve controlled release during swelling and contraction. However, hydrogel-based slow-release fertilizers have the following problems: (1) Insufficient mechanical strength: The three-dimensional network structure of traditional hydrogels (such as sodium alginate) is fragile and easily breaks under soil pressure or during cultivation, resulting in nutrient leakage. (2) Risk of sudden release after swelling: After absorbing water and swelling, the network pores increase, and nutrients are easily released quickly, making it impossible to achieve long-term slow supply (such as nitrogen release rate exceeding 60% within 72 hours). (3) Weak environmental adaptability: In acidic soil (pH<5.5) or high-salt environment, the swelling performance decreases and the nutrient release efficiency decreases; the cross-linking stability is poor at low temperatures, affecting the slow-release effect. (4) Poor long-term stability: It is easily degraded by soil microorganisms (such as cellulose-based hydrogels), or the network structure is fatigued and broken due to repeated swelling and contraction. Summary of the Invention

[0005] To address the problems of severe microplastic pollution in traditional slow-release fertilizers, low nutrient content in biochar fertilizers, and poor mechanical strength and stability of hydrogel-based biochar fertilizers, this invention aims to provide a biochar composite hydrogel slow-release fertilizer, its preparation method, and its applications. This invention proposes an "in-situ gelation within pores" strategy, preparing hydrogels in situ within the pores of biochar to produce a biochar composite hydrogel slow-release fertilizer. This slow-release fertilizer exhibits high bonding strength between biochar and hydrogel, resulting in high mechanical strength and possessing both slow-release fertilizer functionality and soil-improving capabilities.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] In a first aspect, the present invention provides a biochar composite hydrogel slow-release fertilizer, comprising biochar, hydrogel fixed in the pores and surface of the biochar, and elemental fertilizer mixed inside the hydrogel, wherein the hydrogel is made of metal cations and alginate.

[0008] In this invention, hydrogels are present both inside and on the surface of the biochar, with elemental fertilizers contained within the hydrogels. The hydrogels are primarily located within the pores of the biochar. The second soaking with metal cations is to enhance the cross-linking strength of the outermost hydrogel layer.

[0009] The mass ratio of biochar, elemental fertilizer, and hydrogel is 1:0.3-0.45:3.2-3.65. The ratio of biochar to hydrogel is mainly determined by the porosity of the biochar. Too high a proportion of elemental fertilizer will reduce gel strength, while too low a proportion will reduce fertilizer load.

[0010] Secondly, the present invention provides a method for preparing the above-mentioned biochar composite hydrogel slow-release fertilizer, comprising the following steps:

[0011] S1: Soak the biochar in a multivalent metal cation solution and then filter it;

[0012] S2: Add elemental fertilizer to the alginate solution to form a hydrogel precursor solution, place the biochar filtered in step S1 into it, let it stand to react and then filter.

[0013] S3: Soak the product filtered in step S2 in a multivalent metal cation solution, let it stand, filter, and dry to obtain the final product.

[0014] In one or more embodiments, in step S1, biochar is obtained from biomass through thermochemical depolymerization. The biochar needs to be sieved through a 10-30 mesh screen. Biochar can be produced by the pyrolysis of agricultural and forestry waste, and it possesses a high specific surface area, a rich pore structure (microporous-mesoporous hierarchical structure), and a stable carbon skeleton. Biochar fertilizer can improve soil water retention and cation exchange capacity (CEC), and can also sequestrate carbon and reduce emissions, adsorbing heavy metals and organic pollutants.

[0015] Furthermore, biomass refers to renewable organic materials derived from living or recently living biological organisms, including the organism itself, its metabolic products, byproducts, and waste. These biological organisms include, but are not limited to, plants, animals, and microorganisms. Forms of biomass include, but are not limited to: wood and forestry residues, crops, agricultural residues and energy crops, algae and aquatic plants, animal manure, organic portions of domestic waste, food processing waste, sewage sludge, and intermediate products or derivatives produced from any of the aforementioned substances through physical, chemical, and / or biological treatment processes. Examples of biomass include lignin, sawdust, and rice husks.

[0016] Furthermore, thermochemical depolymerization includes pyrolysis and hydrothermal carbonization. For example, the hydrothermal carbonization step can involve a hydrothermal reaction at 200-300℃ (e.g., 200℃, 210℃, 220℃, 230℃, 240℃, 250℃, 260℃, 270℃, 280℃, 290℃, 300℃, etc.) for 2-6 hours (e.g., 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, etc.). The pyrolysis step can involve high-temperature calcination at 600-800℃ (e.g., 600℃, 650℃, 700℃, 750℃, 800℃, etc.) for 5-60 minutes (e.g., 5 minutes, 10 minutes, 15 minutes, 20 minutes, 25 minutes, 30 minutes, 40 minutes, 50 minutes, 60 minutes, etc.), with a heating rate of 10-20℃ / min.

[0017] In one or more embodiments, in steps S1 and S3, the polyvalent metal cation is one or more of the following: calcium, magnesium, barium, strontium, zinc, copper, iron, and aluminum ion solutions. The polyvalent metal cations in steps S1 and S3 may be the same or different.

[0018] In one or more embodiments, in step S1, the concentration of the polyvalent metal cation is 0.01-0.4 mol / L. For example, it can be 0.01 mol / L, 0.05 mol / L, 0.1 mol / L, 0.15 mol / L, 0.2 mol / L, 0.25 mol / L, 0.3 mol / L, 0.35 mol / L, 0.4 mol / L, etc., or specific values ​​between these ranges.

[0019] In one or more embodiments, in step S3, the concentration of the polyvalent metal cation is 0.4-1.0 mol / L. For example, it can be 0.45 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1 mol / L, or specific values ​​between these ranges.

[0020] It should be noted that the concentration of the polyvalent metal cation solution in step S3 is equal to or higher than the concentration of the polyvalent metal cation solution in step S1. To achieve better technical results, it is preferable that the concentration of the polyvalent metal cation solution in step S3 is higher than the concentration of the polyvalent metal cation solution in step S1. Because the metal ions enter the biochar first, followed by the alginate solution, the hydrogel crosslinking density formed by the alginate that enters the biochar later is lower. The purpose of soaking the metal cations again in step S3 is to increase the crosslinking density of the outermost layer (the part that enters the biochar later), which can improve both the hydrogel strength and its sustained-release effect.

[0021] In one or more embodiments, in step S2, the concentration of alginate in the precursor solution of the hydrogel is 2-5 wt%, such as 2 wt%, 3 wt%, 4 wt%, 5 wt%, etc., or specific values ​​between these points. The alginate is sodium alginate or potassium alginate.

[0022] The reason for choosing alginate is that after the biochar is soaked and filtered in a multivalent metal cation solution in step S1, a large number of metal cations will remain in the pores of the biochar. When alginate is added at this time, the metal cations in the pores of the biochar will undergo a displacement reaction with the metal ions (such as sodium ions) in the alginate, thereby achieving in-situ gelation in the pores of the biochar. In the process, the elemental fertilizer in the hydrogel precursor solution is also fixed in the pores of the biochar, thus achieving the fixed filling of elemental fertilizer and gel in the pores of the biochar.

[0023] In one or more embodiments, in step S2, the elemental fertilizer includes one or more of urea, ammonium nitrate, diammonium phosphate, superphosphate, tripotassium phosphate, potassium nitrate, potassium chloride, ammonium polyphosphate, potassium sulfate, and potassium dihydrogen phosphate. The amount of each element added to the elemental fertilizer is 10-20% of the hydrogel precursor solution. If multiple elements are added, the ratio of the amounts of each element can be 1:1.

[0024] In one or more embodiments, in step S2, the concentration of the elemental fertilizer in the precursor solution of the hydrogel is 0-300 g / L. For example, it can be 0 g / L, 1 g / L, 25 g / L, 50 g / L, 100 g / L, 150 g / L, 200 g / L, 250 g / L, 300 g / L, etc., or specific values ​​between these ranges. Excessive addition of the elemental fertilizer will affect the in-situ gelation of alginate and metal cations within the pores.

[0025] In one or more embodiments, in step S2, the settling time is 20-60 minutes, such as 20 minutes, 25 minutes, 30 minutes, 35 minutes, 40 minutes, 45 minutes, 50 minutes, 55 minutes, 60 minutes, etc., or specific values ​​between these points. A settling time of this duration allows for a sufficient displacement reaction between alginate and metal cations, resulting in in-situ gelation of the biochar and simultaneous in-situ fixation of the slow-release fertilizer elements within the pores of the biochar.

[0026] In one or more embodiments, in step S3, the settling time is 2-15 minutes, such as 2 minutes, 3 minutes, 4 minutes, 5 minutes, 6 minutes, 7 minutes, 8 minutes, 9 minutes, 10 minutes, 11 minutes, 12 minutes, 13 minutes, 14 minutes, 15 minutes, etc., or specific values ​​between these points. In step S3, the biochar composite hydrogel slow-release fertilizer initially formed in step S2 is placed again in a higher concentration of metal cation buffer solution to allow the remaining unreacted alginate and metal cations to react fully.

[0027] In one or more embodiments, the crosslinking temperature used in steps S2 and S3 is room temperature.

[0028] In a preferred embodiment, the preparation method of the biochar composite hydrogel slow-release fertilizer includes:

[0029] (1) Biochar is prepared by thermochemical depolymerization of biomass.

[0030] (2) Soak the biochar in a solution containing polyvalent metal cations and then filter it out.

[0031] (3) Prepare the precursor solution of the hydrogel and add a large amount of element fertilizer to the precursor solution.

[0032] (4) Place the filtered biochar from step (2) into the hydrogel precursor solution containing nitrogen, phosphorus and potassium fertilizer obtained in step (3) and let it stand for reaction.

[0033] (5) After filtering the biomass carbon from step (4) after the reaction is complete, soak it thoroughly in a high-concentration polyvalent metal cation solution.

[0034] (6) The biochar obtained in step (5) is filtered to obtain a biochar composite hydrogel, and then dried to obtain a biochar composite hydrogel slow-release fertilizer.

[0035] Thirdly, this invention provides the application of the above-mentioned biochar composite hydrogel slow-release fertilizer in the agricultural field.

[0036] One or more of the above technical solutions have the following advantages or beneficial effects:

[0037] (1) This invention prepares biochar composite hydrogel slow-release fertilizer through an "in-situ gelation within pores" strategy. Hydrogel is prepared in situ within the pores of biochar, and fertilizer is simultaneously fixed in situ within the biochar pores. The biochar framework enhances the mechanical strength of the hydrogel, slows down microbial decomposition, and the adsorption of free nutrients by the biochar pores, in conjunction with the hydrogel's control of the diffusion rate, forms a dual slow-release barrier. The biochar composite hydrogel slow-release fertilizer possesses both the function of slowing fertilizer release and the ability to improve soil.

[0038] (2) The biochar composite hydrogel slow-release fertilizer prepared by the present invention can achieve a long-term slow-release effect. The slow-release ratio of the fertilizer reaches more than 95% after 48 days and more than 97% after 60 days. Attached Figure Description

[0039] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0040] Figure 1 The images show actual photos of the biochar and the biochar composite hydrogel slow-release fertilizer prepared according to the present invention; wherein, a is an actual photo of the biochar and b is an actual photo of the biochar composite hydrogel slow-release fertilizer.

[0041] Figure 2 SEM images of the biochar and biochar composite hydrogel slow-release fertilizer prepared in this invention; wherein, a is the SEM image of biochar and b is the SEM image of biochar composite hydrogel slow-release fertilizer.

[0042] Figure 3 The infrared spectrum of the biochar and biochar composite hydrogel slow-release fertilizer prepared in this invention. Detailed Implementation

[0043] In this invention, unless otherwise specified, all other test materials and instruments are conventional test materials in the field and can be purchased through commercial channels.

[0044] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0045] Example 1

[0046] Take 20g of dried lignin, place it in a quartz tube, and directly immerse it in a tube furnace at 650℃ under a nitrogen atmosphere for 10 min. Allow it to cool naturally to room temperature, grind it through a 20-mesh sieve to obtain lignin biochar. Place the biochar in a 0.1mol / L calcium chloride solution and stir magnetically for 30 min. After filtration, place it in a solution of sodium alginate (3 wt%) and urea (15 wt%), let it stand for 30 min, and then filter again. Place the second filtered biochar composite hydrogel in a 0.8mol / L calcium chloride solution, let it stand for 5 min, filter, and wash to obtain the biochar composite hydrogel slow-release fertilizer.

[0047] Example 2

[0048] Take 50 g of dried pine sawdust and place it in a high-pressure reactor. Add 300 mL of deionized water for hydrothermal carbonization: heat to 220°C and maintain the temperature for 4 hours. Allow it to cool naturally to room temperature, grind it through a 20-mesh sieve to obtain pine biochar. Place the biochar in a 0.1 mol / L calcium chloride solution and stir magnetically for 30 min. After filtration, place it in a solution of sodium alginate (3 wt%), potassium nitrate (10 wt%), and diammonium phosphate (10 wt%), let it stand for 30 min, and then filter again. Place the biochar composite hydrogel, which has been filtered again, into a 0.8 mol / L calcium chloride solution, let it stand for 5 min, filter, and wash to obtain the biochar composite hydrogel slow-release fertilizer.

[0049] Example 3

[0050] Take 20g of dried lignin, place it in a quartz tube, and directly immerse it in a tube furnace at 650℃ under a nitrogen atmosphere for 10 min. Allow it to cool naturally to room temperature, grind it through a 20-mesh sieve to obtain lignin biochar. Place the biochar in a 0.05mol / L magnesium sulfate solution and stir magnetically for 30 min. After filtration, place it in a solution of sodium alginate (3 wt%), urea (10 wt%), and diammonium phosphate (10 wt%), let it stand for 30 min, and then filter again. Place the second filtered biochar composite hydrogel in a 0.4mol / L magnesium sulfate solution, let it stand for 5 min, filter, and wash to obtain the biochar composite hydrogel slow-release fertilizer.

[0051] Example 4

[0052] Take 20g of dried rice husks and place them in a quartz tube. Heat the tube to 600℃ at a rate of 15℃ / min under a nitrogen atmosphere and maintain the temperature for 1 hour. Allow it to cool naturally to room temperature, then grind it through a 20-mesh sieve to obtain lignin biochar. Place the biochar in a 0.1 mol / L zinc chloride solution and stir magnetically for 30 min. After filtration, place it in a solution of potassium alginate (3 wt%), urea (10 wt%), and diammonium phosphate (10 wt%), let it stand for 30 min, and then filter again. Place the second filtered biochar composite hydrogel in a 0.4 mol / L magnesium sulfate solution, let it stand for 5 min, then filter and wash to obtain the biochar composite hydrogel slow-release fertilizer.

[0053] Comparative Example 1

[0054] Unlike Example 1, the two soaking processes in the metal cation solution were omitted.

[0055] If not soaked in a solution of metal cations, alginate and metal cations cannot undergo a displacement cross-linking reaction, and thus cannot form a hydrogel.

[0056] Comparative Example 2

[0057] Unlike Example 1, the initial soaking process of biochar in the metal cation solution is retained, but the final soaking process with metal cations is omitted. If the second metal cation soaking process is omitted, the slow-release effect of the fertilizer will decrease.

[0058] Comparative Example 3

[0059] Unlike Example 1, in this case, alginate and metal cations first form a hydrogel, and then biochar and elemental fertilizers are added to it. In this case, the hydrogel, elemental fertilizers, and biochar separate from each other and cannot form a slow-release fertilizer.

[0060] Comparative Example 4

[0061] Unlike Example 1, biochar and elemental fertilizers such as urea are mixed to obtain urea-loaded biochar. Then, metal cations and alginate are added to form a hydrogel. The hydrogel crosslinks on the surface of the urea-loaded porous biochar, forming hydrogel-encapsulated urea-loaded porous biochar. In this case, the hydrogel can only adhere to the surface of the biochar and cannot penetrate into the interior, thus failing to achieve the dual-effect slow-release effect of hydrogel and biochar, resulting in a decreased slow-release effect.

[0062] Comparative Example 5

[0063] Unlike Example 1, when biochar, urea, metal cations and alginate are mixed together, a hydrogel cannot be formed and there is no sustained-release effect.

[0064] Comparative Example 6

[0065] Unlike Example 1, when metal cations, alginate, and urea are mixed and then mixed with biochar, the hydrogel is merely mixed with the biochar and cannot penetrate into the biochar. Therefore, the dual-effect sustained-release effect of hydrogel plus biochar cannot be formed, and the sustained-release effect is reduced.

[0066] Figure 2 SEM images of the biochar and biochar composite hydrogel slow-release fertilizer prepared according to this invention are shown; where a is the SEM image of the biochar and b is the SEM image of the biochar composite hydrogel slow-release fertilizer. Figure 2 It can be seen that the pores on the surface of biochar have all disappeared and have been filled by hydrogel.

[0067] Figure 3 The image shows the infrared spectrum of the biochar and biochar composite hydrogel slow-release fertilizer prepared according to this invention. Figure 3 As shown in Table 1, it is indeed a biochar composite hydrogel slow-release fertilizer that has been synthesized, containing elements such as fertilizer and sodium alginate.

[0068] Table 1. Assignment of some absorption peaks in the infrared spectrum

[0069]

[0070] Methods for testing the slow-release effect of fertilizers:

[0071] Mix 1.0 g of sample with 60 g of dry soil and add the mixture to the experimental apparatus. Add distilled water until the soil is saturated. Add 20 mL of distilled water to the apparatus periodically, keeping the drain valve open, and collect the leachate for nitrogen nutrient content determination.

[0072] The fertilizer slow-release effects of the materials prepared in various embodiments and comparative examples are shown in Table 2. As can be seen from Table 2, the biomass carbon composite hydrogel slow-release fertilizer prepared in the embodiments of the present invention achieves a long-term slow-release effect. The slow-release ratio of the fertilizer only reaches over 95% after 48 days, and only over 97% after 60 days. In contrast, in the comparative examples, such as Comparative Example 2, a release ratio of 92% was achieved after 13 days, and in Comparative Examples 4 and 6, a release ratio of 90% was achieved after 7 days. Therefore, none of the comparative examples achieved a long-term slow-release effect, while the in-situ hydrogel formation technique within the pores of the present invention can significantly prolong the slow-release effect of the fertilizer.

[0073] Table 2. Release ratio of elemental fertilizers in slow-release fertilizers at different times (%)

[0074]

[0075] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A biochar composite hydrogel slow-release fertilizer, characterized in that, It includes biochar, hydrogels fixed in the pores and surface of biochar, and elemental fertilizers mixed inside the hydrogels, wherein the hydrogels are made from metal cations and alginates; The mass ratio of biochar, elemental fertilizer, and hydrogel is 1:0.3-0.45:3.2-3.65; The preparation method of the biochar composite hydrogel slow-release fertilizer includes the following steps: S1: Soak the biochar in a multivalent metal cation solution and then filter it; S2: Add elemental fertilizer to the alginate solution to form a hydrogel precursor solution, place the biochar filtered in step S1 into it, let it stand to react and then filter. S3: Soak the product filtered in step S2 in a multivalent metal cation solution, let it stand, filter, and dry to obtain the final product.

2. The biochar composite hydrogel slow-release fertilizer according to claim 1, characterized in that, In step S1, biochar is obtained by thermochemical depolymerization of biomass.

3. The biochar composite hydrogel slow-release fertilizer according to claim 2, characterized in that, Biochar needs to be sieved through a 10-30 mesh.

4. The biochar composite hydrogel slow-release fertilizer according to claim 2, characterized in that, Thermochemical depolymerization includes pyrolysis and hydrothermal carbonization.

5. The biochar composite hydrogel slow-release fertilizer according to claim 4, characterized in that, The temperature for hydrothermal carbonization is 200~300℃, and the reaction time is 2~6h.

6. The biochar composite hydrogel slow-release fertilizer according to claim 4, characterized in that, The pyrolysis temperature is 600~800℃, and the pyrolysis time is 5~60min.

7. The biochar composite hydrogel slow-release fertilizer according to claim 1, characterized in that, In steps S1 and S3, the polyvalent metal cations are one or more of the following: calcium, magnesium, barium, strontium, zinc, copper, iron, and aluminum ion solutions; wherein the polyvalent metal cations in steps S1 and S3 may be the same or different.

8. The biochar composite hydrogel slow-release fertilizer according to claim 7, characterized in that, In step S1, the concentration of polyvalent metal cations is 0.01-0.4 mol / L.

9. The biochar composite hydrogel slow-release fertilizer according to claim 7, characterized in that, In step S3, the concentration of the polyvalent metal cation is 0.4-1.0 mol / L; The concentration of the polyvalent metal cation solution in step S3 is equal to or higher than the concentration of the polyvalent metal cation solution in step S1.

10. The biochar composite hydrogel slow-release fertilizer according to claim 1, characterized in that, In step S2, the concentration of alginate in the precursor solution of the hydrogel is 2-5 wt%.

11. The biochar composite hydrogel slow-release fertilizer according to claim 10, characterized in that, The alginate is sodium alginate or potassium alginate.

12. The biochar composite hydrogel slow-release fertilizer according to claim 1, characterized in that, In step S2, the elemental fertilizer includes one or more of the following: urea, ammonium nitrate, diammonium phosphate, superphosphate, tripotassium phosphate, potassium nitrate, potassium chloride, ammonium polyphosphate, potassium sulfate, and potassium dihydrogen phosphate.

13. The biochar composite hydrogel slow-release fertilizer according to claim 12, characterized in that, In step S2, the concentration of elemental fertilizer in the precursor solution of the hydrogel is 0-300 g / L.

14. The biochar composite hydrogel slow-release fertilizer according to claim 1, characterized in that, In step S2, the settling time is 20~60 minutes.

15. The biochar composite hydrogel slow-release fertilizer according to claim 1, characterized in that, In step S3, the settling time is 2~15 minutes.

16. The application of the biochar composite hydrogel slow-release fertilizer according to any one of claims 1-15 in the agricultural field.

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