Fertiliser granules

Abstract

This invention relates to a fertiliser granule comprising a pozzolanic material and a biochar. Suitably, the pozzolanic material is poultry litter ash. The present invention also relates to methods of making the fertiliser granules, and methods of promoting plant growth.

Description

Fertiliser Granules

[0001] The present invention relates to a fertiliser granule comprising a pozzolanic material and a biochar. Suitably, the pozzolanic material is poultry litter ash. The present invention also relates to methods of making the fertiliser granules, and methods of promoting plant growth.BACKGROUND

[0002] The United Nations Food and Agriculture Organisation has predicted that by 2050, the global population will rise to 9.7 billion. Accordingly, the global demand for food production continues to increase, in line with population growth. Many technologies have been developed to improve crop yields and food quality, and the use of chemical fertiliser is a widespread solution for achieving this. For example, the application of chemical fertilisers to agricultural production contributes to approximately 50% extra crop yield. However, the over-use and suboptimal utilisation of chemical fertilisers causes the decline of fertiliser efficiency, in addition to significant environmental problems.

[0003] Nitrogen fertiliser is the most consumed fertiliser. However, nitrogen fertilisers undergo ammonia volatilisation, nitrate leaching, and nitrous oxide release, causing pollution of surface water, groundwater, and the atmosphere. Further, only 20 to 30% of nitrogen in fertilisers is actually taken up by crops and plants.

[0004] Phosphorus also plays an important role in crop growth in agriculture production, and as such, phosphorus fertilisers are also widely used. However, limited natural reserves mean that high-quality phosphate resources are becoming depleted. Phosphorus fertilisers also suffer from low availability of soluble phosphorus for plant uptake. Additionally, excessive phosphorus fertilisation significantly enlarges the risk of phosphorus loss through leaching, runoff, and erosion. Not only does this cause serious environmental pollution, but it also results in significant financial loss. Furthermore, excessive application of chemical fertilisers is one of the lead causes for the deteriorating state of soils.

[0005] To overcome the challenges faced by conventional chemical fertiliser over-use, slow- release fertilisers have been developed in recent years. These fertilisers delay and thus prolong the availability of their nutrients for plant uptake. This is advantageous as slow- release fertilisers reduce nutrient loss and leaching into the environment.

[0006] Biochar is a carbon-rich solid material derived from pyrolysis of biogenic material. The process of biomass pyrolysis, when operated correctly, captures more carbon dioxide than it emits and is recognised by the IPCC as a Carbon Capture technology. Biochar possessesseveral properties that make it attractive as a resource material for several applications such as soil amendments, waste management, carbon sequestration, and energy storage. Biochar has therefore recently emerged as an attractive candidate for use as a slow-release fertiliser. However, biochar possesses limited nutrients which are necessary for fertilisers.

[0007] The present invention seeks to provide a biochar-based slow-release fertiliser which can ameliorate or overcome some or all of the above problems faced by conventional chemical fertilisers. In particular, a fertiliser that improves Nitrogen Use Efficiency and comprises a carbon-negative formulation.BRIEF SUMMARY OF THE DISCLOSURE

[0008] In a first aspect of the invention, there is provided a fertiliser granule comprising a pozzolanic material and a biochar.

[0009] It may be that the fertiliser granule comprises biochar distributed through a matrix of the pozzolanic material.

[0010] The inventors have found that fertiliser granules comprising both biochar and a pozzolanic material have a unique combination of properties. They are hard enough to be applied to the rhizosphere using existing agricultural machinery but are also able break down on exposure to moisture in order to release the biochar and minerals. The inventors have found that, once the fertiliser granules are applied to the rhizosphere, the fertiliser granules slowly absorb water from the soil, and gradually disintegrate. As the fertiliser granules disintegrate, the biochar particles within the fertiliser granules act to hold potassium and phosphorus in the rhizosphere. This reduces leaching and also provides a slow-release fertiliser. After initial sowing, and after subsequent application of a nitrogen source to the crop cycle (such as synthetic nitrogenous fertiliser), the biochar particles within the fertiliser granules act to absorb and hold nitrogen compounds in the rhizosphere, thus reducing leaching and losses to air, thereby increasing nitrogen use efficiency (NUE). Advantageously, due this increase in NUE, the farmer can reduce the amount of nitrogen source applied to the soil whilst maintaining the yield. Moreover, the carbon-negative nature of the fertiliser granule, and the resultant carbon savings made by applying less nitrogenous fertiliser, leads to significant environmental and economic benefits.

[0011] In a second aspect of the invention, there is provided a method of making a fertiliser granule, the method comprising:blending a pozzolanic material and a biochar in the presence of a wetting agent to form uncured granules; and allowing the granules to cure to form fertiliser granules.

[0012] In this embodiment, it may be that the method further com prises producing the biochar. It may be that the wetting agent is water.

[0013] In a third aspect of the invention, there is provided a method of promoting plant growth, the method comprising applying the fertiliser granules as described herein to soil in which the plants are intended to grow.

[0014] In this embodiment, it may be that the method further comprises applying a nitrogen source to the soil.

[0015] In a fourth aspect of the invention, there is provided a method of promoting plant growth, the method comprising applying the fertiliser granules obtained by the method described herein to soil in which the plants are intended to grow.

[0016] In this embodiment, it may be that the method further comprises applying a nitrogen source to the soil.Pozzolanic Material

[0017] In embodiments, the pozzolanic material is a mineral rich ash, such as poultry litter ash, meat and bonemeal ash, wood ash, rice husk ash, or olive stone ash. Thus, it may be that the pozzolanic material is selected from poultry litter ash, meat and bonemeal ash, wood ash, rice husk ash, or olive stone ash. It may be that the pozzolanic material is selected from poultry litter ash, or meat and bonemeal ash. Preferably, the pozzolanic material is poultry litter ash. It may be that the pozzolanic material is rock dust, such as basalt rock dust.

[0018] In embodiments, the fertiliser granule comprises one or more pozzolanic materials. Thus, it may be that the pozzolanic material is selected from poultry litter ash, meat and bonemeal ash, wood ash, rice husk ash, or olive stone ash, or combinations thereof. It may be that the pozzolanic material is selected from poultry litter ash, meat and bonemeal ash, wood ash, rice husk ash, olive stone ash, or basalt rock dust, or combinations thereof. It may be that the fertiliser granule comprises one pozzolanic material. For example, it may be that the fertiliser granule comprises poultry litter ash. It may be that the fertiliser granule comprises two pozzolanic materials. For example, it may be that the fertiliser granule comprises poultry litter ash, and meat and bonemeal ash. It may be that the fertiliser granule comprises three pozzolanic materials.

[0019] It will be understood that the pozzolanic material will be selected to meet the requirements of the crop. The pozzolanic material may comprise an NPK ratio in the range of from N0-P30-K15 to N0-P15-K10.

[0020] In embodiments, the pozzolanic material has a particle size distribution such that at least 80% by weight of the pozzolanic material is below 20 microns. It may be that the pozzolanic material has a particle size distribution such that at least 80% by weight of the pozzolanic material is below 10 microns. It may be that the pozzolanic material has a particle size distribution such that at least 80% by weight of the pozzolanic material is below 5 microns. In preferred embodiments, the pozzolanic material is poultry litter ash (PLA). Thus, it may be that the PLA has a particle size distribution such that at least 80% by weight of the PLA is below 20 microns. It may be that the PLA has a particle size distribution such that at least 80% by weight of the PLA is below 10 microns. It may be that the PLA has a particle size distribution such that at least 80% by weight of the PLA is below 5 microns. It will be understood that the particle size distribution of the pozzolanic material can be determined by any suitable means known in the art. For example, it may be that the particle size distribution of the pozzolanic material is determined by a particle size analyser, e.g. a Mastersizer 2000 (Malvern Instruments).

[0021] In embodiments, the moisture content of the pozzolanic material is below 25% by weight of the pozzolanic material. It may be that the moisture content of the pozzolanic material is below 20% by weight of the pozzolanic material. It may be that the moisture content of the pozzolanic material is below 15% by weight of the pozzolanic material. In preferred embodiments, the pozzolanic material is poultry litter ash (PLA). Thus, it may be that the moisture content of the PLA is below 25% by weight of the PLA. It may be that the moisture content of the PLA is below 20% by weight of the PLA. It may be that the moisture content of the PLA is below 15% by weight of the PLA. It will be understood that the moisture content of the pozzolanic material can be determined by any suitable means known in the art. For example, it may be that the moisture content of the pozzolanic material is determined with the loss on drying method. For example, it may be that the pozzolanic material is oven dried at 105 °C for 24 hours, and the moisture is determined from the direct weight lost by the sample due to heating. It may be that the moisture content of the pozzolanic material is determined with a moisture analyser (such as a Mettler Toledo HC103 Halogen Moisture Analyser).

[0022] In embodiments, the pozzolanic material has an NPK ratio in the range of from N0-P1- K1 to N2-P50-K30. It may be that the pozzolanic material has an NPK ratio in the range of from N0-P10-K5 to N2-P40-K25. It may be that the pozzolanic material has an NPK ratio in the range of from N0-P20-K10 to N1-P30-K20, for example, an NPK ratio in the range of fromN0-P30-K15 to N0-P15-K10. Preferably, it may be that the pozzolanic material is PLA. Thus, it may be that the PLA has an NPK ratio of N0-P30-K15. The NPK ratio of the pozzolanic material can be determined by any suitable means known in the art.

[0023] Poultry litter ash (PLA) is created through a thermal process. This thermal process generates a combination of different ashes, each with varying levels of phosphorus and potassium. These different ashes (referred to as “fly ash” and “bottom ash”) may be used separately, or they can be blended together to achieve the desired phosphorus and potassium profile of the ash. “Fly ash” is also known as high temperature PLA. It is so called “fly ash”, as this ash flies around in the combustion chamber until it is collected and filtered out. “Bottom ash” is also known as low temperature PLA. It is so called “bottom ash”, as this ash falls to the bottom of the combustion chamber during the thermal process.

[0024] Accordingly, in the context of the present invention, any reference to PLA encompasses both the individual and / or the combination of ashes generated in the thermal process of creating PLA. Thus, it may be that the PLA comprises fly ash. It may be that the PLA comprises bottom ash. It may be that the PLA comprises fly ash and bottom ash.

[0025] The skilled person will be aware that fertiliser analyses and inputs are expressed in oxide form for phosphorus and potassium (generally P2O5 and K2O). Therefore, reference herein to ‘phosphorus’ or ‘P’ in the pozzolanic material, generally refers to P2O5. Reference herein to ‘potassium’ or ‘K’ in the pozzolanic material, generally refers to K2O. However, reference to nitrogen (N) encompasses a range of nitrogen containing compounds, including, but not limited to ammonia, ammonium salts and urea.

[0026] Thus, in embodiments, the pozzolanic material comprises from 0% to 5% of nitrogen by weight of the pozzolanic material. It may be that the pozzolanic material comprises from 0% to 2% of nitrogen by weight of the pozzolanic material. It may be that the pozzolanic material comprises from 0% to 1 % of nitrogen by weight of the pozzolanic material. It may be that the pozzolanic material does not comprise nitrogen.

[0027] In embodiments, the pozzolanic material comprises from 1% to 50% of phosphorus by weight of the pozzolanic material. It may be that the pozzolanic material comprises from 10% to 40% of phosphorus by weight of the pozzolanic material. It may be that the pozzolanic material comprises from 20% to 30% of phosphorus by weight of the pozzolanic material.

[0028] In embodiments, the pozzolanic material comprises from 1% to 30% of potassium by weight of the pozzolanic material. It may be that the pozzolanic material comprises from 5% to 25% of potassium by weight of the pozzolanic material. It may be that the pozzolanic material comprises from 10% to 20% of potassium by weight of the pozzolanic material.Biochar

[0029] In embodiments, in the fertiliser granule (or in the central portion of the fertiliser granule), the biochar is distributed through a matrix of the pozzolanic material.

[0030] In embodiments, the biochar is present in the fertiliser granule in an amount of from 30% to 90% of the total weight of the fertiliser granules. It may be that the biochar is present in an amount of from 40% to 80% of the total weight of the granules. It may be that the biochar is present in an amount of from 50% to 70% of the total weight of the fertiliser granules. It may be that the biochar is present in an amount no more than 65% of the total weight of the fertiliser granules. It may be that the biochar is present in an amount of from 10% to 65% of the total weight of the fertiliser granules. It may be that the biochar is present in an amount of from 20% to 65% of the total weight of the fertiliser granules. It may be that the biochar is present in an amount of from 30% to 65% of the total weight of the fertiliser granules. It may be that the biochar is present in an amount of from 40% to 65% of the total weight of the fertiliser granules. It may be that the biochar is present in an amount of from 50% to 65% of the total weight of the fertiliser granules.

[0031] In embodiments, the average particle size of the biochar is in the range of from 50 microns to 200 microns. It may be that the average particle size of the biochar is in the range of from 75 microns to 150 microns. It may be that the average particle size of the biochar is in the range of from 90 microns to 110 microns. It may be that the average particle size of the biochar is about 100 microns.

[0032] In embodiments, the moisture content of the biochar is below 25% by weight of the biochar. It may be that the moisture content of the biochar is below 20% by weight of the biochar. It may be that the moisture content of the biochar is below 15% by weight of the biochar. It may be that the moisture content of the biochar is below 10% by weight of the biochar. It will be understood that the moisture content of the biochar can be determined by any suitable means known in the art. For example, it may be that the moisture content of the biochar is determined with the loss on drying method. For example, it may be that the biochar is oven dried at 105 °C for 24 hours, and the moisture is determined from the direct weight lost by the sample due to heating. It may be that the moisture content of the biochar is determined with a moisture analyser (such as a Mettler Toledo HC103 Halogen Moisture Analyser).

[0033] In embodiments, the biochar has a carbon content of from 60% to 90% by weight of the biochar. It may be that the biochar has a carbon content of from 65% to 85% by weight of the biochar. It may be that the biochar has a carbon content of from 70% to 80% by weight of the biochar, for example, 80% by weight of the biochar. It will be understood that the carboncontent of the biochar depends on the feedstock and pyrolysis temperature used to generate the biochar.The Fertiliser Granules

[0034] It will be understood that the hardness of the fertiliser granules must be such that the fertiliser granules can pass through the agricultural machinery when the granules are applied to the soil. The inventors have also found that the hardness of the fertiliser granules also plays a key factor in allowing water to penetrate the granule, such that the granule softens and disintegrates in the soil. The rate of disintegration of the fertiliser granule is important, so that the biochar particles within the fertiliser granules are ready to absorb the nitrogen compounds in the nitrogen source (e.g. a nitrogen fertiliser) which is subsequently applied to the crop. The hardness of the fertiliser granules can be tailored by varying the relative proportions of the biochar and the pozzolanic material, the type or strength of the pozzolanic material, in addition to the curing method and curing time.

[0035] It may be that granule comprises biochar distributed through a matrix of the pozzolanic material. It may be that the fertiliser granule comprises a central portion and one or more outer portions in which the central portion comprises said matrix of the pozzolanic material with the biochar distributed through. The outer portion or outer portions may be continuous. Any given outer portion may, however, be discontinuous.

[0036] It may be that the one or more outer portions are selected from: an outer portion of biochar, an outer portion of the pozzolanic material, and an outer portion of blended biochar and pozzolanic material having a different composition than that of the central portion. It may be that the fertiliser granule comprises a central portion and one outer portion. Thus, it may be that the outer portion is biochar. It may be that the outer portion is the pozzolanic material. It may be that the outer portion is a blend of biochar and pozzolanic material having a different composition than that of the central portion. It may be that the outer portion is a blend of biochar and pozzolanic material having the same composition of the central portion. The fertiliser granule may comprise a central portion and two or more outer portions. It may be that the fertiliser granule comprises a central portion and two or more outer portions selected from: an outer portion of biochar, an outer portion of the pozzolanic material, and an outer portion of blended biochar and pozzolanic material having a different composition than that of the central portion.

[0037] It may be that the outer portion is a material (other than biochar and a pozzolanic material) that controls exposure of the biochar and / or pozzolanic material to the surrounding conditions, e.g. a polymer.

[0038] Preferably, it may be that the fertiliser granule comprises a central portion and an outer portion of biochar. It may be that this outer portion acts as an additional barrier to slow the release rate of the nutrients from the central portion of the granule, to the intended plants. However, it is understood that the fertiliser granules still act as a slow-release fertiliser, without the presence of the outer portion. Thus, in other embodiments, it may be that the fertiliser granule does not comprise an outer portion.

[0039] In embodiments, the fertiliser granule comprises about 30% biochar and 70% pozzolanic material, by weight of the fertiliser granule. It may be that the fertiliser granule comprises about 10% biochar and 90% pozzolanic material, by weight of the fertiliser granule. It may be that the fertiliser granule comprises about 20% biochar and 80% pozzolanic material, by weight of the fertiliser granule. It may be that the fertiliser granule comprises about 40% biochar and 60% pozzolanic material, by weight of the fertiliser granule. It may be that the fertiliser granule comprises about 50% biochar and 50% pozzolanic material, by weight of the fertiliser granule. It may be that the fertiliser granule comprises about 60% biochar and 40% pozzolanic material, by weight of the fertiliser granule. It may be that the fertiliser granule comprises about 65% biochar and 35% pozzolanic material, by weight of the fertiliser granule. It may be that the pozzolanic material is PLA. Therefore, it may be that the fertiliser granule comprises about 30% biochar and 70% PLA, by weight of the fertiliser granule. It may be that the fertiliser granule comprises about 40% biochar and 60% PLA, by weight of the fertiliser granule. It may be that the fertiliser granule comprises about 10% biochar and 90% PLA, by weight of the fertiliser granule. It may be that the fertiliser granule comprises about 20% biochar and 80% PLA, by weight of the fertiliser granule. It may be that the fertiliser granule comprises about 50% biochar and 50% PLA, by weight of the fertiliser granule. It may be that the fertiliser granule comprises about 60% biochar and 40% PLA, by weight of the fertiliser granule. It may be that the fertiliser granule comprises about 65% biochar and 35% PLA, by weight of the fertiliser granule. In embodiments, the fertiliser granule has a hardness of at least about 20 N immediately after curing at ambient temperature. In embodiments, the fertiliser granule has a hardness of at least about 20 N after 2 days curing at ambient temperature. In embodiments, the fertiliser granule has a hardness of at least about 60 N after 7 days curing at ambient temperature. In embodiments, the fertiliser granule has a hardness in the range of from 20 N to 100 N after 30 days of curing at ambient temperature. Accordingly, when the fertiliser granule is applied to soil in which plants are intended to grow, the fertiliser granule has a hardness in the range of from 20 N to 100 N. It may be that the fertiliser granule has a hardness in the range of from 20 N to 100 N. It may be that the fertiliser granule has a hardness in the range of from 30 N to 80 N. It may be that the fertiliser granule has a hardness in the range of from 30 N to 50 N, for example, about 40 N. In embodiments, the fertilisergranule has a hardness in the range of from 20 N to 100 N up to 90 days in storage. In embodiments, the fertiliser granule has a hardness in the range of from 20 N to 100 N up to ten weeks in storage. It may be that the fertiliser granule has a hardness in the range of from 30 N to 100 N. It may be that the fertiliser granule has a hardness in the range of from 10 N to 40 N when measured 10 weeks after application to the soil.

[0040] The skilled person will be aware that fertiliser analyses and inputs are expressed in oxide form for phosphorus and potassium (generally P2O5 and K2O). Therefore, reference herein to ‘phosphorus’ or ‘P’ in the fertiliser granule, generally refers to P2O5. Reference herein to ‘potassium’ or ‘K’ in the fertiliser granule, generally refers to K2O. However, reference to nitrogen (N) encompasses a range of nitrogen-containing compounds, including, but not limited to ammonia, ammonium salts and urea.

[0041] In embodiments, the fertiliser granule has an NPK ratio in the range of from N1-P1-K1 to N10-P50-K30. It may be that the fertiliser granule has an NPK ratio in the range of from N1-P10-K5 to N5-P40-K25. It may be that the fertiliser granule has an NPK ratio in the range of from N1-P20-K10 to N3-P30-K20, for example, an NPK ratio of N1-P30-K15.

[0042] In embodiments, the fertiliser granules comprise from 1% to 10% of nitrogen by weight of the fertiliser granules. It may be that the fertiliser granules comprise from 1 % to 5% of nitrogen by weight of the fertiliser granules. It may be that the fertiliser granules comprise from 1% to 3% of nitrogen by weight of the fertiliser granules.

[0043] In embodiments, the fertiliser granules comprise from 1% to 50% of phosphorus by weight of the fertiliser granules. It may be that the fertiliser granules comprise from 10% to 40% of phosphorus by weight of the fertiliser granules. It may be that the fertiliser granules comprise from 20% to 30% of phosphorus by weight of the fertiliser granules.

[0044] In embodiments, the fertiliser granules comprise from 1% to 30% of potassium by weight of the fertiliser granules. It may be that the fertiliser granules comprise from 5% to 25% of potassium by weight of the fertiliser granules. It may be that the fertiliser granules comprise from 10% to 20% of potassium by weight of the fertiliser granules.

[0045] It may be that the fertiliser granules (i.e. after curing) are screened to achieve the required diameter. It may be that the screening process comprises sieving the fertiliser granules in order to remove the granules which are smaller or larger than the required diameter. Thus, it may be that the fertiliser granules (i.e. after curing) have a diameter in the range of from 1 mm to 10 mm. It may be that the fertiliser granules have a diameter in the range of from 2 mm to 4 mm. It may be that the fertiliser granules have a diameter in the range of from 4 mm to 6 mm. It may be that the fertiliser granules have a diameter in therange of from 6 mm to 8 mm. It may be that the fertiliser granules are screened such that at least about 95% of the fertiliser granules have a diameter in the range of from 2 mm to 4 mm.The Method of Making Fertiliser Granules

[0046] In embodiments, prior to step a) the pozzolanic material and the biochar are blended before the addition of a wetting agent such as water. This is to ensure that the pozzolanic material and the biochar are thoroughly mixed prior to the granulation process. The pozzolanic material and the biochar can be blended by any suitable means known in the art. For example, the pozzolanic material and the biochar can be blended with a ribbon blender.

[0047] In step a), the pozzolanic material and the biochar are blended in the presence of a wetting agent to form uncured granules. Typically, the wetting agent comprises water. Typically, the wetting agent comprises enough water to trigger the pozzolanic reaction to form cementitious hydration products. In embodiments, the wetting agent is selected from, but not limited to, water, urine and / or liquid digestate. Preferably, the wetting agent is water. Thus, it may be that in step a), the pozzolanic material and the biochar are blended in the presence of water to form uncured granules.

[0048] In embodiments, step a) is conducted in an intensive mixer. Accordingly, the pozzolanic material and the biochar are blended in the presence of a wetting agent (e.g. water) in an intensive mixture to form uncured granules. It may be that the intensive mixer is a high shear rotary mixture. Thus, it may be that step a) is conducted in a high shear rotary mixture.

[0049] In embodiments, the speed of the mixer (e.g. the intensive mixer) is reduced during the course of step a). Reducing the speed of the mixture induces granule growth (granulation). Thus, it may be that the speed of the mixer (e.g. the intensive mixer) is reduced during the course of step a) to induce granule growth.

[0050] It may be that the uncured granule of step a) comprises biochar distributed through a matrix of the pozzolanic material. It may be that the uncured granule of step a) comprises a central portion, wherein the central portion comprises said matrix of the pozzolanic material with the biochar distributed through. It may be that the uncured granule of step a) comprises a central portion and one or more outer portions in which the central portion comprises said matrix of the pozzolanic material with the biochar distributed through. The outer portion or outer portions may be continuous. Any given outer portion may, however, be discontinuous.

[0051] It may be that the one or more outer portions are added to the central portion of the uncured granule in step a). It may be that the one or more outer portions are selected from: an outer portion of biochar, an outer portion of the pozzolanic material, an outer portion of blended biochar and pozzolanic material having a different composition than that of the centralportion, and an outer portion of blended biochar and pozzolanic material having the same composition of the central portion. It may be that one outer portion is added to the central portion of the uncured granule in step a). Thus, it may be that the outer portion is biochar, and said biochar is added to the central portion of the uncured granule in step a). It may be that the outer portion is the pozzolanic material, and said pozzolanic material is added to the central portion of the uncured granule in step a). It may be that the outer portion is a blend of biochar and pozzolanic material having a different composition than that of the central portion, and said blend is added to the central portion of the uncured granule in step a). It may be that the outer portion is a blend of biochar and pozzolanic material having the same composition of the central portion, and said blend is added to the central portion of the uncured granule in step a). It may be that the central portion of the uncured granule in step a) is dusted with the outer portion.

[0052] It may be that two or more outer portions are added to the central portion of the uncured granule in step a), wherein the outer portions are selected from: an outer portion of biochar, an outer portion of the pozzolanic material, an outer portion of blended biochar and pozzolanic material having a different composition than that of the central portion, and an outer portion of blended biochar and pozzolanic material having the same composition of the central portion.

[0053] It may be that the outer portion is a material (other than biochar and a pozzolanic material) added to the central portion of the uncured granule in step a), that controls exposure of the biochar and / or pozzolanic material in the cured fertiliser granule of step b) to the surrounding conditions, e.g. a polymer.

[0054] Preferably, it may be that the outer portion is biochar, and said biochar is added to the central portion of the uncured granule in step a). Thus, it may be that the central portion of the uncured granule in step a) is dusted with biochar.

[0055] In other embodiments, it may be that an outer portion is not added to the central portion of the uncured granule in step a).

[0056] It may be that an outer portion as defined herein is added to the central portion of the uncured granule in step a), to absorb any excess moisture produced by the uncured granules during the granulation process.

[0057] In embodiments, the uncured granules of step a) have a diameter in the range of from about 0.5 mm to 10 mm. It may be that the uncured granules of step a) have a diameter in the range of from about 1 mm to 10 mm. It may be that the uncured granules of step a) have a diameter in the range of from about 1 mm to 5 mm, for example, in the range of from 2 mm to 4 mm.

[0058] In embodiments, the uncured granules of step a) have a hardness of less than 10 N. It may be that the uncured granules of step a) have a hardness of less than 5 N. It may be that the uncured granules of step a) have a hardness of less than 2 N. It may be that the hardness of the uncured granules is measured by a hand-held fertiliser hardness tester.

[0059] Typically, the uncured granules are not at the required hardness to pass through the agricultural machinery when they are applied to the soil. Thus, the uncured granules are cured to the required hardness for application to the soil. In some embodiments, the granules cure (harden) at ambient temperature and as such, heat is not required to cure the granules. Thus, it may be that in step b) the granules are cured at ambient temperature to form fertiliser granules. For example, it may be that in step b) the granules are cured at a temperature of from 5 °C to 30 °C to form fertiliser granules. It may be that in step b) the granules are cured at a temperature of from 10 °C to 25 °C to form fertiliser granules. It may be that in step b) the granules are cured at a temperature of from 18 °C to 22 °C to form fertiliser granules.

[0060] In other embodiments, in step b) the granules are cured at an elevated temperature to form fertiliser granules, such as in an oven or a drying tunnel. Thus, it may be that the granules are cured at a temperature of from 40 °C to 120 °C to form fertiliser granules. It may be that the granules are cured at a temperature of from 50 °C to 100 °C to form fertiliser granules. It may be that the granules are cured at a temperature of from 60 °C to 80 °C to form fertiliser granules. Curing (i.e. drying), or partially curing (i.e. partially drying) the fertiliser granules at elevated temperatures can enable greater control over the hardness of the granules and the timescale of their subsequent disintegration in the soil, and thus the rate at which they release nutrients. For example, a fertiliser granule that has been cured at an elevated temperature may have a reduced hardness, and therefore disintegrate over a shorter period of time in the soil. By contrast, a fertiliser granule that has been cured at an ambient temperature may have an increased hardness, and therefore disintegrate over a longer period of time in the soil.

[0061] In embodiments, in step b) the granules are cured for up to 30 days to form fertiliser granules. Thus, it may be that in step b) the granules are cured for 1 day to 30 days to form fertiliser granules, for example, for 1 day, for 2 days, for 7 days, or for 30 days to form fertiliser granules. Preferably, it may be that in step b) the granules are cured at ambient temperature (e.g. from 5 °C to 30 °C) for 1 day to 30 days to form fertiliser granules, for example, for 1 day, for 2 days, for 7 days, or for 30 days to form fertiliser granules.

[0062] In embodiments, the method further comprises producing the biochar.Producing the biochar

[0063] Biochar is a carbon-rich solid material derived from biomass, produced through the thermochemical transformation of biomass feedstocks. Such thermochemical processes include pyrolysis, gasification, and hydrothermal carbonisation. Biomass feedstocks include both plant- and animal-derived biomass feedstocks. Thus, in embodiments, the biochar is produced by pyrolysis of plant-derived biomass feedstocks, such as cereal straw or biomass energy crops.

[0064] In embodiments, the biochar is produced by pyrolysis of cereal straw or biomass energy crops. It may be that the biochar is produced by pyrolysis of cereal straw. It may be that the biochar is produced by pyrolysis of biomass energy crops. Thus, the biochar may be produced by pyrolysis of any suitable cereal straw or biomass energy crop known in the art. It may be that the cereal straw or biomass energy crops are selected from, but not limited to, wheat, barley, rape, hemp, corn stover, miscanthus, rice grain husk, rice straw, coconut shell, cocoa bean pod, or combinations thereof. Thus, it may be that the biochar is produced by pyrolysis of wheat, barley, rape, hemp, corn stover, miscanthus, rice grain husk, rice straw, coconut shell, or cocoa bean pod. For example, it may be that the biochar is produced by pyrolysis of wheat straw.

[0065] In embodiments, the cereal straw or biomass energy crops used to produce the biochar have an average size in the range of from 1 mm to 50 mm. It may be that the cereal straw or biomass energy crops used to produce the biochar have an average size in the range of from 5 mm to 30 mm. It may be that the cereal straw or biomass energy crops used to produce the biochar have an average size in the range of from 10 mm to 20 mm. The cereal straw or biomass energy crops used to produce the biochar are reduced to the appropriate size using suitable particle size reduction (PSR) technology, such as a debaler and hammermill.

[0066] In embodiments, the cereal straw or biomass energy crops used to produce the biochar have a moisture content of below 25% by weight of the cereal straw or biomass energy crops. It may be that the cereal straw or biomass energy crops used to produce the biochar have a moisture content of below 20% by weight of the cereal straw or biomass energy crops. It may be that the cereal straw or biomass energy crops used to produce the biochar have a moisture content of below 15% by weight of the cereal straw or biomass energy crops.

[0067] In embodiments, the cereal straw or biomass energy crops are pyrolyzed at a temperature of from 300 °C to 1000 °C. It may be that the cereal straw or biomass energy crops are pyrolyzed at a temperature of from 400 °C to 800 °C. the cereal straw or biomass energy crops are pyrolyzed at a temperature of from 500 °C to 700 °C, for example, about 650 °C. It may be that the cereal straw or biomass energy crops are pyrolyzed at a temperaturedefined herein for up to 30 minutes. For example, from 1 minute to 30 minutes, from 1 minute to 20 minutes, or from 5 minutes to 10 minutes.

[0068] The average particle size of the biochar must be reduced prior to granulation. This may be achieved by dry milling, for example, in a ball-mill, or an air classifier. In embodiments, the biochar is reduced to an average particle size in the range of from 10 microns to 200 microns. It may be that the biochar is reduced to an average particle size in the range of from 50 microns to 200 microns. It may be that the biochar is reduced to an average particle size in the range of from 75 microns to 150 microns. It may be that the biochar is reduced to an average particle size in the range of from 90 microns to 110 microns. For example, it may be that the biochar is reduced to an average particle size of about 100 microns. Accordingly, the average particle size of the biochar in step a) is in the range of from 10 microns to 200 microns.

[0069] In embodiments, the moisture content of the biochar is below 25% by weight of the biochar. It may be that the moisture content of the biochar is below 20% by weight of the biochar. It may be that the moisture content of the biochar is below 15% by weight of the biochar, for example 10% by weight of the biochar.The Methods of Promoting Plant Growth

[0070] In embodiments, the method comprises applying the fertiliser granules described herein to soil in which plants are growing or to soil in which plants are intended to grow. Preferably, the method comprises applying the fertiliser granules described herein to soil in which plants are intended to grow. In these embodiments, the method further comprises applying a nitrogen source to the soil.

[0071] In embodiments, the method comprises applying the fertiliser granules obtained by the method described herein to soil in which plants are growing or to soil in which plants are intended to grow. Preferably, the method comprises applying the fertiliser granules obtained by the method described herein to soil in which plants are intended to grow. In these embodiments, the method further comprises applying a nitrogen source to the soil.

[0072] In embodiments, the nitrogen source is biogenic or synthetic. It may be that the nitrogen source is a biogenic nitrogen source. It may be that the nitrogen source is a synthetic nitrogen source (e.g. a mineral fertiliser). It may be that the nitrogen source is a nitrogenous fertiliser. It may be that the nitrogen source is a liquid nitrogen fertiliser. It may be that the nitrogen source further comprises a sulphur source. Thus, it may be that the nitrogen source is a liquid nitrogen and sulphur fertiliser. For example, it may be that the nitrogen source is Chafer Nuram 35+S (Yara). Chafer Nuram 35+S (35% N + 7% SO3) is a liquid nitrogen andsulphate fertiliser, wherein the N content is 8.1% nitrate w / v, 10.6% ammoniacal w / v and 16.3% ureic.

[0073] In embodiments, the fertiliser granules are applied to the soil via a spinning disc spreader, a seed drill, a no-till seed-drill or banding. Preferably, it may be that the fertiliser granules are applied to the soil via a seed-drill. When the fertiliser granules are applied via the seed drill, the fertiliser granules are applied directly to the rhizosphere. This optimises the performance of the fertiliser granules. Thus, it may be that the fertiliser granules are applied directly to the rhizosphere.

[0074] It may be that the fertiliser granules are applied to the soil with the seed. It may be that the fertiliser granules are applied to the soil before the seed. It may be that the fertiliser granules are applied to the rhizosphere. It may be that the fertiliser granules are applied to the rhizosphere with the seed. It may be that the fertiliser granules are applied to the rhizosphere before the seed.

[0075] It may be that the fertiliser granules are applied to the soil at a rate of 1 tonne per hectare. It may be that the fertiliser granules are applied to the soil at a rate of 2 tonnes per hectare.

[0076] The phosphorus and potassium levels present in soil varies depending on the amounts of these nutrients removed by the preceding crop. The components of the fertiliser granules of the present invention can therefore be carefully tailored in order to replenish the phosphorus and potassium levels in the soil required by the succeeding crop (also known as the replenishment values).

[0077] Once the fertiliser granules are applied to the soil, they begin to soften and disintegrate. The rate of granule disintegration is controlled by the formulation of the granules and influenced by the prevailing soil conditions, particularly total soil moisture. The total soil moisture can be determined by any suitable means in the art, such as the drying and gravimetric method. Granules with a high biochar content disintegrate more quickly than granules with a low biochar content. Granules comprising a strongly pozzolanic material such as high temperature PLA (i.e. PLA fly ash) disintegrate more slowly than those made from a weakly pozzolanic material such as wood ash.

[0078] Accordingly, by varying the composition of the fertiliser granule, it is possible to create a slow-release fertiliser granule tailored to the crop agronomy.

[0079] In embodiments, the fertiliser granules soften up to 10 days after they are applied to the soil. It may be that the fertiliser granules soften up to 20 days after they are applied to the soil. It may be that the fertiliser granules soften up to 30 days after they are applied to thesoil. The skilled person will understand that the rate at which the fertiliser granules soften and disintegrate will depend on, but not limited to, the following factors: exposure to rainfall, pozzolanic material strength index, the ratio of biochar to pozzolanic material, granule size, soil pH, invertebrate activity in the soil, or combinations thereof. To determine the fertiliser granule softness, the fertiliser granules can be measured by any suitable method known in the art, such as the methods to determine fertiliser granule hardness (i.e. granule crush strength) described herein.

[0080] As discussed above, the granules disintegrate via water absorption by the biochar particles which absorb water from the surface layer formed around each granule. The absorbed water is then absorbed further into the granule until full hydration is achieved. At this point, the pozzolanic particles no longer maintain structural integrity and the granule disintegrates. If too little biochar is incorporated into the formulation the pozzolans will maintain integrity and the granules will not disintegrate, inhibiting the agronomical benefits described below.

[0081] As the granules disintegrate several effects occur. Firstly, the pH around the granule is modified to be alkaline, which in turn makes the phosphorus released from the disintegrating granule more available to the developing plants and less likely to be lost through leaching.

[0082] Secondly, as the granules disintegrate, the biochar particles become dispersed further in the soil and are subsequently colonised by soil micro fauna (including nitrogen fixing bacteria) and mineralised with plant nutrients. Thus, holding them in the rhizosphere and reducing losses due to leaching. Further, the large surface area of the porous biochar particles ensures that the cationic exchange capacity of the soil is increased, thereby increasing nutrient use efficiency (NUE) overall.

[0083] When chemical nitrogen fertilisers are subsequently applied to the soil, the biochar particles adsorb the nitrogen compounds due to their high surface area, and the bacteria involved in the nitrogen cycle make the nitrogen available to the growing plants.

[0084] The overall Nitrogen Use Efficiency of the applied nitrogen fertiliser is thereby improved, allowing the farmer to reduce the total nitrogen applied whilst maintaining yield.

[0085] Typically, the granule disintegration is fully complete prior to the first application of nitrogen fertiliser. Thus, it may be that the nitrogen source (e.g. nitrogen fertiliser) is applied to the soil about 16 weeks after the application of the fertiliser granules. It may be that the nitrogen source (e.g. nitrogen fertiliser) is applied to the soil about 20 weeks after the application of the fertiliser granules. It may be that the nitrogen source (e.g. nitrogen fertiliser) is applied to the soil about 24 weeks after application of the fertiliser granules. It will beappreciated that much of the arable land in the UK is designated to be a Nitrate Vulnerable Zone (NVZ). This means that there are strict controls on when, and how much nitrogen fertiliser can be applied to the fields. It is therefore envisaged that one advantage of the present invention is that the fertiliser granules described herein may unlock NVZ status by intercepting nitrate runoff, so that NVZ is no longer required.

[0086] It will also be understood that the application of the nitrogen source to the soil (after application of the fertiliser granules) will depend on when the crop seeds are sown. For example, once the seeds are sown, a nitrogen source may not be applied to the soil until the crop has emerged and the plants are becoming established (for example, about 4 months after the seeds are sown). In this instance, the plants are able to use the nitrogen applied to the soil. It may also be that two separate nitrogen sources are applied to the soil. For example, it may be that a nitrogen source is applied about 4 months after the seeds were sown, and a further nitrogen source is applied about 6 months after the seeds were sown.

[0087] Thus, it may be that more than one nitrogen source is applied to the soil after the application of the fertiliser granules. For example, it may be that the first nitrogen source (e.g. nitrogen fertiliser) is applied to the soil about 16 weeks, about 20 weeks, or about 24 weeks after the application of the fertiliser granules. It may be that a second nitrogen source (e.g. nitrogen fertiliser) is applied to the soil about 8 weeks, about 12 weeks, or about 16 weeks after the application of the first nitrogen source.

[0088] It may be that the fertiliser granules are applied to the rhizosphere to encourage root growth. It may be that the nitrogen source is then applied to the crops once the leaves have developed chlorophyll.BRIEF DESCRIPTION OF THE DRAWINGS

[0089] Embodiments of the invention are further described hereinafter with reference to the accompanying drawings:Figure 1 is bar chart showing the difference in breakforce (or hardness or crush strength) of fertiliser granules as applied (at T=0); after 90 days under ambient conditions; after 10 weeks under ambient conditions; and after 10 weeks in soil.Figure 2A is an SEM / EDX image of an unused fertiliser granule. Figure 2B is an SEM / EDX image of a fertiliser granule after 10 weeks in soil. After 10 weeks in soil, the fertiliser granule showed the-migration of phosphorus and potassium into the soil.Figure 3 is an image of a Rhizobox containing ten winter wheat seedlings each of which have been fertilised with a single fertiliser granule.Figure 4 shows images depicting the difference in above ground sprouting (tillering) of winter wheat when fertiliser granules are not used (in the control) and when they are used (Biochar).Figure 5 shows the tracing of below ground roots of winter wheat when fertiliser granules are not used (in the control) and when they are used (Biochar).DETAILED DESCRIPTION

[0090] Unless otherwise stated, the following terms used in the specification and claims have the following meanings set out below.

[0091] The term “biochar” refers to any biogenic material (such as cereal straw or biomass energy crops) that has been carbonised under high temperatures (e.g. 300 to 1000 °C), in the presence of little, or no oxygen. This process (called “pyrolysis”) releases bio-oils and gases, but leaves a solid residue of at least about 60% elemental carbon which is termed “biochar”. The process of biomass pyrolysis, when operated correctly, captures more carbon dioxide than it emits and is recognised by the IPCC as a Carbon Capture technology.

[0092] The term “pozzolanic material” refers to a material with an amorphous siliceous or siliceous and aluminous content that reacts with calcium hydroxide in the presence of water to form cementitious hydration products (such as calcium silicate hydrates and calcium silicate aluminate hydrates). It will be understood that when the pozzolanic material is present in a formed fertiliser granule of the present invention, the pozzolanic material has already reacted in the presence of a wetting agent (such as water) and therefore has already formed the cementitious hydration products. Suitably, in the context of the present invention, the “pozzolanic material” is also a source of potassium and / or phosphorus.

[0093] The pozzolanic material may contain >25% by weight (wt%) SiO2. The pozzolanic material may contain >30 wt% SiO2. The pozzolanic material may contain >10 wt% AI2O3. Pozzolanic materials may contain AI2O in the range from between 10-30 wt%. Pozzolanic materials may contain combined SiO2and AI2O3in the range from between 35-70 wt%. Pozzolanic materials may contain combined SiO2and AI2O3in the range from between 40- 60 wt%.

[0094] Pozzolanic materials may also contain calcium oxide (CaO), which, when mixed with water, hydrates to form calcium hydroxide (Ca(OH)2) in an exothermic reaction. The Ca(OH)2then participates in the pozzolanic reaction with silica (SiO2) and alumina (AI2O3) to form cementitious hydration products. Such a pozzolanic material is PLA.

[0095] The pozzolanic activity of PLA can be evaluated by mixing it with water and detecting a temperature rise due to the exothermic hydration of CaO into Ca(OH)2. A typical mixing ratio for this test is 9 parts pozzolanic material to 1 part water. The PLA may be mixed with ambient tap water in a polyethylene bag. An increase in temperature (e.g. detected by hand), indicates the pozzolanic reactivity of the material. This method can be used to determine whether any granules formed from blending the PLA with biochar will exhibit the desired pozzolanic activity.

[0096] The pozzolanic material (e.g. PLA) may contain <50 wt% CaO. The pozzolanic material (e.g. PLA) may contain CaO in the range from between 5-50 wt%. The pozzolanic material (e.g. PLA) may contain CaO in the range from between 10-40 wt%.

[0097] The chemical composition of the pozzolanic material (e.g., SiO2, AI2O3, and CaO levels) can be determined using standard analytical methods such as those described in ASTM C618.

[0098] The term “poultry litter ash” or “PLA” refers to the ash produced from the incineration of poultry litter, feathers and / or straw.

[0099] The term “NPK ratio” is the amount (%) of nitrogen ‘N’ (in the form of nitrogencontaining compounds such as, but not limited to, ammonia, ammonium salts and urea), phosphorus ‘P’ (generally in the oxide form of P2O5) and potassium ‘K’ (generally in the oxide form of K2O) present in the material, by weight of the material. For example, a fertiliser granule with an NPK ratio of N1-P30-K15, means that said fertiliser granule comprises 1 % nitrogen (in the form of nitrogen-containing compounds), 30% phosphorus (generally in the form of P2O5), and 15% potassium (generally in the form of K2O), by weight of the fertiliser granule.

[0100] The term “slow-release” fertilisers herein refers to fertilisers that degrade slowly over time when in contact with soil, and thus provide controlled release, extended (or sustained) release or delayed release or any combination thereof of the components within the fertiliser.

[0101] Reference to “hardness” of the fertiliser granules and / or uncured granules described herein refers to the granule crush strength. Thus, these terms can be used interchangeably throughout this specification. For example, it may be that the fertiliser granule has a hardness in the range of from 20 N to 100 N. Accordingly, it may also be that the fertiliser granule has a granule crush strength in the range of from 20 N to 100 N. It may be that the uncured granules have a hardness of less than 10 N. Accordingly, it may also be thatthe uncured granules have a granule crush strength of less than 10 N. The hardness of the granules (i.e. the granule crush strength) may be determined by any suitable means known in the art. For example, by crushing a granule between two metal plates and recording the force using a load cell. Therefore, the hardness of the granules (i.e. the granule crush strength) may be measured using automated equipment such as the Mecmesin Multitest-dv (motorised force tester), or a hand-held fertiliser hardness tester such as the SCS Fert Analysis Kit Crush Strength Tester. Thus, it may be that the hardness of the granules (i.e. the granule crush strength) is measured using a hand-held fertiliser hardness tester (such as a SCS Fert Analysis Kit Crush Strength Tester), wherein an average of at least three readings are taken of similar sized granules. Preferably, an average of at least five readings are taken of similar sized granules.

[0102] The term “ambient temperature” refers to a temperature in the range of from 5 °C to 30 °C. It may be that ambient temperature refers to a temperature in the range of from 10 °C to 25 °C. It may be that the term ambient temperature refers to a temperature in the range of from 18 °C to 22 °C. It will be understood that the ambient temperature can fluctuate within this range. For example, when the fertiliser granules of the invention are cured at ambient temperature, it may be that the temperature fluctuates between about 10 °C and about 22 °C, depending on the time of day.

[0103] Reference to “about” in the context of a numerical is intended to encompass the value + / - 10%. For example, about 20% includes the range of from 18% to 22%.

[0104] The particle size average and the particle size distribution of a material (e.g. pozzolanic material or biochar) can be determined by any suitable means known in the art. For example, by a particle size analyser. The particle size analyser may be a laser diffraction particle size analyser, e.g. a Mastersizer 2000 (Malvern Instruments), which is specifically designed to analyse the particle size of powders. The particle size average and the particle size distribution can be automatically determined from the tabulated data and a frequency distribution curve (histogram) generated by the laser diffraction particle analyser.

[0105] Throughout the description and claims of this specification, the words “comprise” and “contain” and variations of them mean “including but not limited to”, and they are not intended to (and do not) exclude other moieties, additives, components, integers or steps. Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

[0106] Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and / or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and / or steps are mutually exclusive. The invention is not restricted to the details of any foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

[0107] For the avoidance of doubt, the information disclosed earlier in this specification under the heading “Background” is relevant to the invention and is to be read as part of the disclosure of the invention.

[0108] The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.EXAMPLESExample 1 - Method for preparing fertiliser granules1) Preparation of Biochar

[0109] Cereal straw bales with a maximum moisture content of 18% were broken down using a bale-breaker or shredder such as a KIDD 850 bale shredder. The resultant loosely chopped straw was transferred to a proprietary straw shredder and processed until the feedstock was in the average size range of from 10 mm to 20 mm.

[0110] The chopped cereal straw was then dried in a dryer to achieve a target of 10% moisture by weight. The dryer was heated using syngas from the pyrolysis process downstream.

[0111] The chopped and dried cereal straw was mechanically conveyed via a flighted conveyor to the pyrolysis unit where it was pyrolyzed at a peak temperature of 650 °C for a target residence time of 7 minutes. The syngas liberated during pyrolysis was recirculated to provide fuel to heat the pyrolysis reaction vessel and the straw dryer.

[0112] Once pyrolyzed, the hot biochar was dispensed via a screw conveyor into a cooling conveyor consisting of a screw rotating within a water-jacketed vessel and supplied with mains potable water.

[0113] Once cooled to 30 °C, the biochar was dispensed into an intermediate bulk container (IBC) and stored uncovered in a holding area (Intermediate storage) until ambient conditions were reached. The IBC can be closed or covered and the biochar can be stored for up to 6 months at ambient temperature and humidity.2) Particle Size Reduction of Biochar

[0114] To prepare the biochar for granulation it is necessary to reduce the particle size until all particles sit in the range of from 50 microns to 200 microns with the average particle size being 100 microns. This can be achieved using dry milling, typically in a ball-mill or air classifier. In order to achieve a consistent product the moisture content of the biochar should be no more than 23% by weight, ideally less than 18%.

[0115] Any pozzolanic material which is intended to be blended with the biochar should also be size-reduced to a similar particle size and moisture profile to ensure consistent granulation.3) Blending of Biochar with Pozzolanic materials

[0116] In this example, the composition comprised of 30% by weight of wheat straw biochar with a carbon content of 80%, and 70% by weight of Poultry Litter Ash with a nutrient ratio of N=0, P=30 and K=15. The Poultry Litter Ash (PLA) is expected to be naturally pozzolanic, however material tests should be undertaken prior to blending to ensure the PLA exhibits an exothermic reaction when mixed with water in the ratio of 9 parts PLA to 1 part tap water. The PLA was mixed with ambient tap water in a polyethylene bag, until a rise in temperature was detected. This indicated that an exothermic reaction is occurring between the calcium oxide within the PLA and the water, which in turn indicates the blend will have the desired pozzolanic character.

[0117] Once the material has been confirmed as pozzolanic, the chosen components can be blended to form a uniform mixture. Blending can be undertaken in any proprietary blender suitable for flours, such as a ribbon blender. Mix homogeneity studies as advised by the equipment manufacturer should be performed to ensure a consistent well-mixed product.4) Granulation

[0118] The process of granulation requires the pore spaces between the particles of the blend to be systematically saturated with water or another suitable wetting agent so thatthe particles are brought close enough together so that Van Der Waals forces allow small spheres to form (nucleation). These spheres or nuclei are then grown through accretion where several nuclei coalesce into a “blackberry” formation. The “blackberry” is consolidated into a coherent granule by squeezing the excess liquid from the pore spaces between the nuclei.

[0119] As pore saturation is taken beyond 100% in the blackberry stage it may be necessary to characterise the dry blend in terms of its water holding capacity prior to granulation for the first time. This can be done using a simple measure of water holding capacity (WHC) whereby a funnel with filter paper is filled with a known weight of the blend and a measured amount of water is poured through the funnel, with any excess which is not held by the material being captured in a volumetric flask beneath. The WHC is expressed as a percentage calculated by the weight of water retained by the dry blend divided by the weight of the dry blend.

[0120] The WHC will be specific to each blend and may vary with variation in raw material batches. It is used to indicate how much water to add in total during the granulation process, too little and nuclei will not form, too much and the “blackberries” will coalesce into a “wet slurry” which cannot be recovered.

[0121] To commence the granulation cycle, the required amount of dry powder blend was added to the high intensity mixer chamber, closed, and mixed on high speed. Water was added to the dry powder blend in stages, typically by adding 50% of the expected total initially, (from the WHC test) on high speed. The composition was continuously mixed at high rotor speed and moderate bowl rotation speed until nuclei formation was observed. Additional water was added as necessary, in smaller increments until nuclei were formed.

[0122] Once nuclei were formed, the bowl rotation speed was maintained, and the rotor speed was slowed to a low rotor speed (approximately 10 rpm). This allows the nuclei to grow to the blackberry stage, where all the powder in the mixer is incorporated into the blackberries. The mixer was continued at a slow rotor speed, and water was added as necessary, until the blackberries coalesced and formed coherent granules. It may be necessary to add more dry material at this stage because the blackberries expel excess pore water as they coalesce into granules, and if the pore water is not absorbed it will cause the granules to form a wet slurry.

[0123] This step of adding more dry material (i.e. the outer portion) to the uncured granules (i.e. the central portion) can be achieved using the dry blend, or any component of the dry blend. In this example, the finishing material was air-classified biochar.

[0124] Once the dry granules had formed, the mixing cycle was complete and the granules were dispensed from the mixer onto a suitable surface for air drying. As at least one of the ingredients is pozzolanic, the granules “cured” (hardened) at ambient temperature.

[0125] At this stage, the uncured granules have a typical diameter of 2 mm to 4 mm and a hardness as measured by a hand-held fertiliser hardness tester (such as the SCS Fert Analysis Kit Crush Strength Tester) of less than 10 N. It may be necessary to screen the granules through a series of sieves to remove dust, over-sized and under-sized granules until the desired diameter range is achieved.

[0126] The granules were left to cure for several days, with the hardness being measured daily. The granules typically have a hardness of 20 N on day 2, rising to 60 N by day 7. Once the granules have achieved 40 N they are robust enough to be applied to the soil through existing agricultural machinery such as a seed drill or spinning disc fertiliser spreader.Example 2 - Detailed method for fertiliser granule production1. A 2 Kg blend of dry powder consisting of 1400 g Poultry Litter Ash (PLA) and 600 g wheat straw Biochar was prepared. Both PLA and Biochar were air classified to an average particle size of 100 microns.2. The dry powder blend of step 1) was placed in a mixing bowl of a Eirich R02 Laboratory Mixer (batch size 2 to 4 Kg).3. The dry powder blend of step 2) was mixed with a bowl speed at 38 Hz, and a mixer speed at 75Hz for 30 seconds.4. 625 mL water was then added to the dry powder blend of step 3), and the blend was further mixed at speeds outlined in 3) for 120 seconds.5. 100 mL water was added to the mixture of step 5), and the mixer speed was reduced to 10 Hz.6. The mixture of step 5) was mixed for 60 seconds, until nucleation occurred.7. The mixer speed was then reduced to 5 Hz, and the mixture of step 6) was mixed for a further 60 seconds, until granulation occurred.8. 145 g Biochar powder (air classified to an average particle size of 100 microns) was then added to the granules of step 7), and mixed for a further 30 seconds. The mixer was then stopped and the uncured granules were retrieved.9. Uncured granules were dispensed onto a solid metal tray, and left to cure at ambient temperature (about 10 °C during the night, and 22 °C during the day).10. Samples were taken to analyse hardness (i.e. crush strength) at T = 0 hours, T = 24 hours, and every subsequent 24 hours until a granule hardness (i.e. crush strength) of about 20 N was achieved. Samples were similarly assessed for moisture content (using the methods described herein).11. Once a minimum hardness (i.e. crush strength) value of about 20 N was reached, the fertiliser granules were dispensed into an IBC and stored at ambient temperature to await transportation to the field.Example 3 - Granule curing and softening, slow nutrient release1) Background

[0127] The fertiliser granules are composed of wheat straw biochar (BC) and poultry litter ash (PLA). The crush strength was monitored over time, from the onset (T=0) through to 90 days at ambient storage.

[0128] The granules were applied to the rhizosphere at approximately 10 cm depth to sit alongside wheat seeds. Periodically some granules were recovered from the soil and their crush strength was tested. Granules were also sent for SEM / EDX analysis. The data below refer to a granule composed of 30 parts BC to 70 parts PLA (which were prepared as described in example 1).2) Method

[0129] The method to evaluate crush strength is an industry standard hand-held plunger used by farmers to evaluate the hardness of fertiliser granules when calibrating spinning disc fertiliser spreaders.

[0130] The tester was supplied by SCS UK, sometimes known as spreadcheck. As the method is manual and therefore prone to a high degree of error a number of repeats were undertaken, usually 5, and the average recorded. This proved to be sufficient to distinguish between recipes and storage duration.3) Resultsparts BC and 70 parts PLA by measuring granule crush strength of in Kg Force (with N in brackets).

[0131] Fig. 1 shows how the granules breakforce (crush strength or hardness) changed over time.

[0132] Fig. 1 and Table 1. also describe how, when applied to the soil, the granules crush strength is lost as it softens. These granules were also compared in Figs. 2A and 2B using SEM / EDX for elemental analysis at T=0 and after 10 weeks in the soil.4) Conclusions and discussion

[0133] The BC I PLA granule forms to have a crush strength sufficient to pass through farm machinery, achieving a crush strength of over 4 Kgf (39 N) at T=0. This compares favourably with the industry standard prilled urea which typically has a crush strength of 2 to 3 Kgf (19N to 30N) and demonstrates that the fertiliser granules can be manufactured using a standard granulation system without the need for additional drying.

[0134] The granule continues to improve in crush strength over time. This is due to the curing of the granule brought about by the pozzolanic nature of the PLA. The granule “cures” in much the same way as cement or concrete, which also exploit the pozzolanic properties of calcium hydroxide in the presence of silicates. This further illustrates the importance of using PLA , as not all biomass ashes exhibit the required level of pozzolanic behaviour.

[0135] These results also indicate that there is a limit to the process capability of granule forming based upon the proportion of BC: PLA. In experiments it was determined that the upper limit for BC inclusion was 65% by weight, meaning formulations containing more than 65% BC did not form granules with a breakforce of >3Kgf.

[0136] The softening observed after some time in the soil is a highly desirable characteristic, as it relates directly to the release of plant nutrients as groundwater penetrates the granule. The SEM / EDX images of Figs. 2A and 2B demonstrate how the Phosphorous and Potassium has left the granule whilst the carbon remains. This is the mechanism by which essential plant nutrients are slowly delivered to the developing plant.

[0137] As the granules were placed directly into the rhizosphere at sowing this nutrient delivery is highly effective during the time in which the plant requires Phosphorus for root development, typically the first ten weeks of growth for winter wheat.

[0138] Varying the proportion of BC to PLA in the granule and observing the hardening prior to soil application and the subsequent softening in the soil provides an opportunity to create a fertiliser granule with controlled nutrient release characteristics. The higher the proportion of BC in the formulation, the faster the granule will soften to release the nutrients.Example 4 - Nitrogen Interception by fertiliser granules1) Background

[0139] A dose response study was conducted which tested yield versus differing doses of biochar fertiliser in a fertilised system and with 50% reduction of fertiliser to that system.

[0140] The fertiliser granules were assessed in a field trial using winter wheat. Five half-hectare plots, designated A to E were sown at a rate of 200 seeds per square metre in October 2023. Each of the 5 plots were subdivided into two equal parts, i.e. A1 , A2, B1 , B2, C1 , C2, D1 , D2, E1 , E2.

[0141] All plots designated 1 (except E1) received a normal level of nitrogenous fertiliser (2 x 90 Kg) which was Nuram liquid applied via a 28m spraybar. All plots designated 2 (except E2) received half the normal level of Nuram (90 Kg). Plot E was totally unfertilised and represented the base fertility of the field. The Nuram was applied in two splits, the first in March 2024 to all plots except E at a rate of 90Kg per hectare (or 9 g / m2). The second split of Nuram was applied in May 2024 but only to plots designated 1 , except E. The second split was also 90Kg per hectare (or 9 g / m2).

[0142] Plots A, B, and C were treated with 130Kg, 240Kg and 420Kg of biochar fertiliser granules, respectively. Plots D and E received no biochar fertiliser granules.2) Evaluation of Nitrogen Requirement

[0143] The farm was registered on the Yara At Farm App and the test plots were assessed using the Yara N-tester which measures chlorophyll development in the leaves. Based upon the results the At Farm application then recommends what additional Nitrogen should be applied to achieve maximum yield at the end of the growing season.

[0144] The test plots were assessed in June 2024, after the second split of Nuram. Yara recommend to take 30 measurements across a field to get an accurate result. Each of the sub-plots in this study were tested one hundred times, to establish a meaningful distribution.

[0145] Plot D1 represents a normally fertilised plot, and plot E2 represents an unfertilised, or baseline fertility situation. Some of the results are observed in Table 2.3) Discussion

[0146] When compared to E2 both B2 and C2 showed a reduced requirement for further Nuram application, as described in Table 2. Plot E2 was assessed for soil organic nitrogen at the start of the trial. This showed it had a baseline fertility of 64Kg of N per hectare (6.4 g / m2of N).

[0147] When evaluating plot E2 the N-tester recommendation was accurate, as a rate of 200 to 220 Kg of N per hectare (20 to 22 g / m2of N) was recognised as the requirement in order to maximise yield in winter wheat. Plot E was predicted to need an additional 144 Kg ofN per hectare (14.4 g / m2of N) in addition to the baseline of 64Kg of N per hectare (6.4 g / m2of N), giving a total of 208Kg of N per hectare (20.8 g / m2of N), in line with expectations.

[0148] Plot D1 was normally fertilised and required no more Nitrogen to optimise yield, as expected.

[0149] Plot B2 only received 50% of the recommended nitrogen application, 90Kg per hectare (9 g / m2of N), yet the N tester recommended only 37Kg of additional nitrogen per hectare (3.7 g / m2of N) was required, versus the expected requirement of 144Kg of N per hectare (14.4 g / m2of N) derived from plot E2 this represents a saving of 17Kg of N per hectare (1 .7 g / m2of N) or 11 .8 % of the total.

[0150] Similarly plot C2 only received 50% of the recommended nitrogen application, 90Kg per hectare (9 g / m2of N), yet the N tester recommended only 20Kg of additional nitrogen per hectare (2 g / m2of N) was required, versus the expected requirement of 144Kg of N per hectare (14.4 g / m2of N) derived from plot E2 this represents a saving of 34Kg of N per hectare (3.4 g / m2of N) or 23.6% of the total.

[0151] Without being bound by theory, the biochar was pyrolyzed at 650 °C for 7 minutes, meaning it would have an overall negative charge on its’ surface. Ammonium ions, with a positive charge, are attracted to the biochar by physisorption. The ammonium ions are then immobilised by chemisorption involving cationic exchange. Most biochars are recognised as having a high cationic exchange capacity. This prevents the ammonium ions being lost to diffuse nutrient pollution and makes them available for plant growth.

[0152] It is this interception that accounts for the reduced requirement for further Nuram addition.

[0153] It is worth noting that the highest level of applied biochar fertiliser resulted in the greatest saving in Nitrogen.Example 5 - Fertiliser impact on winter wheat growth

[0154] In order to understand the impact of the fertiliser granules on the early development of winter wheat, a study was undertaken to grow plants in rhizoboxes.

[0155] Two Plexiglas® (poly[methyl methacrylate]) sheets were held apart by spacers and clamped together. A growing medium was placed into the space created. A line at approximately 20 cm depth was marked on the outside of the box to indicate where the fertiliser granules were placed.

[0156] Eighteen rhizoboxes were created (see Fig. 3). Each box contained a nutrient depleted sandy loam to mimic post-harvest soil. To each was added ten randomly drawn winter wheat seedlings, which were evenly spaced apart. In the nine test variant boxes a single fertiliser granule was placed along the indicator line for each plant. Ten fertiliser granules in total were therefore added to each of the nine test variant boxes. No fertiliser granules were added to the nine control boxes.

[0157] Over a four week growth cycle each box was watered at the same time, and each box was given the same daily amount of ammonium fertiliser. The amount of fertiliser was varied depending on the recommended amount for the growth stage of the plant. The root development was captured every three days by placing tracing paper over the Plexiglas® and tracing the root pattern.

[0158] At the end of the four week study the biomass was harvested and growth data collected from the fresh and dried biomass.Above Ground Biomass Results

[0159] Above ground results are shown in Table 3.granules.

[0160] Biomass measurements were taken at the end of the study, as indicated in Table 3. In all cases the treated boxes showed significant or highly significant levels of change versus the control.

[0161] Tillering is a key indicator of yield potential. As shown in Table 3, the tiller count showed a 211% increase over the control (see also Fig. 4).

[0162] Highly significant results were observed across all plant measures in Table 3. The effect sizes were large for most measures with high level of confidence in effect sizes across the plant measures. Clear clustering and separation between treatment groups was observed when the data was analysed as PCA (87.3% of total variance in the data preserved). Highly significant results were observed when the data was run through PERMANOVA (P <0.001).Below Ground Biomass Results

[0163] Below ground results are shown in Table 4.Table 4. Impact of biomass on below ground segments of plants after a four week growth cycle and harvesting. The control is an average of the nine rhizoboxes that received no fertiliser granules. The treatment is an average of the nine rhizoboxes that received fertiliser granules.

[0164] The treatment showed significant root development versus the control (see Fig. 5), including side rooting, both in the fresh and dried biomass.

[0165] Significant results across all root measures were observed in Table 4. The effect sizes were large for most measures with high level of confidence in effect sizes across the root measures. Biochar roots retained more mass compared to the control roots.Conclusions and Discussions

[0166] The planting density of the winter wheat seedlings in the study equated to a field planting density of 200 seeds per square metre, which is a typical value for winter wheat. The fertiliser granules were applied to the treated boxes at the rate of one per plant, 200 granules per square metre. With each fertiliser granule weighing 0.2g this equates to atreatment of 40g per square metre, or 400kg per hectare. This application rate equates to the maximum amount of fertiliser which was applied in Example 4, 420Kg per hectare, plot C.

[0167] The rhizobox study accurately recreated the field conditions of Example 4 at the time of sowing. The soil was depleted in Potassium and Phosphorus as those nutrients were removed by growing the previous crop. The seed density and fertiliser rate equated to the field study, and water and ammonia fertiliser were applied equally across all boxes and in sufficiency so as not to inhibit plant growth.

[0168] The significant differences observed between the control and treatment boxes can only be explained by the presence or absence of the fertiliser granule.

[0169] The fertiliser granule was formulated to provide replenishment values of Potassium and Phosphorus for winter wheat based on recommendations published by AHDB RB209 Section 4 arable crops and cross checked with recommendations from various agricultural guidance provided by Yara and the Potash Development Association 2023 guidance for Potassium and Phosphorus.

[0170] The fertiliser granule was placed directly into the rhizosphere where the nutrients then become available to support root growth and above ground biomass development.

[0171] The distribution of root development indicated higher levels of side root branching in the treatment boxes as shown in Fig. 5. This is consistent with the known behaviour of roots in the presence of phosphorus i.e. that they are positively phosphotropic.

[0172] Figs. 2A and 2B are SEM / EDX images showing that the fertiliser granule behaves as a slow release fertiliser in the way both Phosphorus and Potassium are released by the granule.

[0173] The significant differences between the control and treatment boxes can be interpreted as the direct result of the fertiliser addition and demonstrate the benefit of this fertiliser granule to plant nutrition in winter wheat.

Claims

CLAIMS1) A fertiliser granule comprising a pozzolanic material and a biochar, wherein the pozzolanic material is poultry litter ash.2) A fertiliser granule of claim 1 , wherein the granule comprises biochar distributed through a matrix of the pozzolanic material.3) A fertiliser granule of claim 2, wherein the fertiliser granule comprises a central portion and one or more outer portions in which the central portion comprises said matrix of the pozzolanic material with the biochar distributed through.4) A fertiliser of claim 3, wherein the one or more outer portions are selected from: an outer portion of biochar, an outer portion of the pozzolanic material, and an outer portion of blended biochar and pozzolanic material having a different composition than that of the central portion.5) A fertiliser granule of any preceding claim, comprising two pozzolanic materials.6) A fertiliser granule of any preceding claim, wherein the biochar is present in an amount of from 30% to 90% of the total weight of the fertiliser granules, optionally wherein the biochar is present in an amount from 30% to 65% of the total weight of the fertiliser granules.7) A fertiliser granule of any preceding claim, wherein the fertiliser granule has a hardness in the range of from 20 N to 100 N.8) A method of making a fertiliser granule, the method comprising: a) blending a pozzolanic material and a biochar in the presence of a wetting agent to form uncured granules, wherein the pozzolanic material is poultry litter ash; and b) allowing the granules to cure to form fertiliser granules.9) A method of claim 8, wherein the fertiliser granule comprises two pozzolanic materials.10) A method of any one of claims 8 to 9, wherein the wetting agent is water.11) A method of any one of claims 8 to 10, wherein the pozzolanic material has a particle size distribution such that at least 80% by weight of the pozzolanic material is below 10 microns.12) A method of any one of claims 8 to 11 , wherein the average particle size of the biochar is in the range of from 10 microns to 200 microns.13) A method of any one of claims 8 to 12, wherein the moisture content of the biochar is below 25% by weight of the biochar.14) A method of any one of claims 8 to 13, wherein the biochar is present in an amount from 30% to 90% of the total weight of the fertiliser granules, optionally wherein the biochar is present in an amount from 30% to 65% of the total weight of the fertiliser granules.15) A method of any one of claims 8 to 14, wherein step a) is conducted in an intensive mixer.16) A method of claim 15, wherein the speed of the mixer is reduced during the course of step a).17) A method of any one of claims 8 to 16, wherein the uncured granules in step a) comprise a central portion, wherein the central portion comprises a matrix of the pozzolanic material with the biochar distributed through.18) A method of claim 17, wherein the method comprises adding one or more outer portions to the central portion, and wherein the one or more outer portions are selected from: an outer portion of biochar, an outer portion of the pozzolanic material, an outer portion of blended biochar and pozzolanic material having a different composition than that of the central portion, and an outer portion of blended biochar and pozzolanic material having the same composition of the central portion.19) A method of any one of claims 8 to 18, wherein the method comprises producing the biochar.20) A method of claim 19, wherein the biochar is produced by pyrolysis of cereal straw or biomass energy crops.21) A method of claim 19 or claim 20 wherein the biochar is reduced to an average particle size in the range of from 50 microns to 200 microns. 22) A method of promoting plant growth, the method comprising applying the fertiliser granules of any one of claims 1 to 7 to soil in which the plants are intended to grow.23) A method of promoting plant growth, the method comprising applying the fertiliser granules obtained by the method of any one of claims 8 to 21 to soil in which the plants are intended to grow.24) A method of claim 22 or claim 23, the method further comprising applying a nitrogen source to the soil, optionally wherein the nitrogen source is Chafer Nuram 35+S (Yara).