Key Practices for effective Nutrient Management in Organic Farming

Organic Agriculture: Benefits and Sustainable Practices

Organic agriculture sustains the health of soils, ecosystems, and people. It relies on ecological processes, biodiversity, and cycles adapted to local conditions, avoiding harmful inputs. Organic agriculture combines tradition, innovation, and science to benefit the environment and promote fair relationships and a good quality of life for all involved (Faux et al., 2021).

Nutrient management on organic farms should economically meet crop nutrient needs and avoid soil nutrient depletion while maintaining or improving soil productivity without excessive nutrient losses. Soil nutrient availability depends on diverse soil chemical, physical, and biological properties, their interactions, and their interaction with the cropping system. While measurements can be made for many soil properties, crop performance is the best indicator of soil productivity. Farmers typically manage to minimize soil physical and chemical constraints to sustainable productivity through practices such as (Thompson, 2021)

• Applying organic materials such as manure, compost, and bio-fertilizers to supply nutrients and maintain soil organic matter. 
• Cultivating cover crops to cycle soil nutrients and biologically fix atmospheric nitrogen.

Fertility Building in Organic Farming

Several routes exist for importing nutrients onto organic farms. However, the cornerstone of the organic philosophy is alternating fertility-building and fertility-depleting phases. 

Nitrogen Management

Organic farming aspires to be nitrogen-self-sufficient through atmospheric nitrogen (N2) fixation, crop residue recycling, and careful management and application of manures and compost. Organic crop rotations frequently incorporate an extra N boost by growing legumes (e.g., field beans or peas) during the fertility-depleting period in addition to legume-based leys.

The effective management of legumes, which capture atmospheric N and convert it to plant-available forms, is critical to developing a successful organic crop rotation. Although recycled plant residues and animal manures assist in maintaining the farm's overall nutritional balance, the only actual nitrogen source is the fixation of N2 by legumes. (Briggs S et al., 2015)

Phosphorus Management

Soil phosphorus supply relies both on microbial activity to convert ('mineralize’) organic P sources and on chemical transformations within the soil. Regulations on organic farming only allow the input of rock phosphates and P-containing organic materials. P-containing organic materials may originate from animal manure, slurry, composts or organic fertilizers (such as guano, blood, horn, bone and fishbone meals, etc.)   (Nesme et al., 2014)

Potassium Management

Regular applications of soluble K, regardless of the source, will increase the concentration of K in the soil solution and the proportion of K on the cation exchange sites. Crushed rocks and minerals have been evaluated as K sources in several fields and greenhouse experiments. Greensand, Langbeinite [potassium–magnesium sulfate (K2SO4-MgSO4)], seaweed, rock powders, sylvinite (KCL), and wood ash are some of the sources of potassium that can be used in organic production. (Mikkelsen, 2007)

Manure management in Organic Farming

Animal feed and bedding are usually the primary sources of nutrients introduced onto the farm. Animal manure is a significant tool for dispersing nutrients across the farm, particularly N, P, K, S, and Mg. Manure is also a good source of organic materials. Fresh manure, particularly slurry and poultry manure, contains a significant amount of N in readily available (mostly ammonium-N) forms that can quickly be lost to the atmosphere. Nutrients (especially N and K) can also be carried away by precipitation. Both ammonia and nitrate losses can pollute the environment and constitute a loss of nitrogen that the crop could use.

Correct manure treatment can reduce nutrient losses and increase crop benefits. The two basic treatment strategies are aerating slurries and actively composting and piling solid manure. Mechanical separation is also an option for slurries.

Composting

Composting is not merely heating organic materials and allowing them to rot. Instead, it is a biological process that requires careful monitoring of air and moisture levels in compost piles or windrows to produce specific temperature ranges that promote the growth of beneficial microorganisms. Compost is the material that results when recycled plant wastes, biosolids (solid materials like manure), fish, and other organic materials decompose aerobically through the action of microorganisms that live in the presence of air. (Baldwin et al., 2009)

Cover crops

Soil physical characteristics, nutrient cycling, and microbial activity can all be improved by cover crops. A cover crop absorbs soil nitrogen that would otherwise be lost through leaching or denitrification if the field were left fallow, reducing potential nitrate pollution and preserving the N in organic form, which becomes available to subsequent crops once the cover crops have been incorporated into the soil. Cover crops also help to keep soil from eroding.(Hue & Silva, 2000) 

However, unlike other organic nitrogen sources, nitrogen in cover crop biomass is not completely available to the next crop. It's crucial to consider the cover crop residue's C: N ratio. In the short term, species with a high C:N ratio (>20:1; e.g., grasses) result in net soil nitrogen immobilization, whereas nitrogen will be more easily available after the breakdown of species with a low C:N ratio (20:1, e.g., legumes). It's crucial to evaluate the total nitrogen concentration of the cover crop residue when employing cover crops for nitrogen management. 

When a cover crop is terminated with a 3 percent nitrogen concentration, the soil input is 60 pounds of organic nitrogen per ton of dry matter. After four weeks, the ammonium-nitrogen release from the organic nitrogen is projected to be 19 pounds per ton, and after ten weeks, it is expected to be 28 pounds per ton. If a producer can produce 3 tons of dry matter per acre of a 3% nitrogen cover crop, around 84 pounds of plant-available nitrogen per acre might be mineralized within 10 weeks after termination. Cover crops may be a sustainable and cost-effective fertilizer source for organic cultivation when combined with other organic amendments to fulfill plant phosphorus, potassium, and micronutrient requirements. For example, rye is frequently used as a winter cover crop to conserve nitrogen and control weeds. A well-managed legume cover crop may fix 150–200 pounds of nitrogen per acre in three to six months.

Crop rotation:

Crop rotation enhances the soil's physical and chemical characteristics, increasing overall fertility. In crop rotations, nitrogen-fixing legumes like soybeans and alfalfa fix atmospheric nitrogen into the soil via root nodules. After that, nitrogen is available for succeeding crops. Deep-rooted cover crops can pull nutrients like potassium and phosphate from deep in the soil profile, making them available to shallow-rooted cash crops later. Tilth and bulk density can be enhanced by growing a hay crop in a rotation. The soil will be loose and have a good granular texture and tilth when a hay crop is plowed. Protecting the soil from rain, the network of fine roots in the soil, and the development of humus from decomposing plant roots all contribute to these increased qualities. Compared to a non-legume as the preceding crop, legumes in the rotation (e.g., beans, alfalfa, or clover) might result in a nitrogen credit for succeeding crops due to biological nitrogen fixing and less nitrogen immobilization. However, because most nitrogen is removed during grain harvest, the nitrogen credit for forage legumes is higher than for grain or vegetable legumes. Forage legumes, on the other hand, produce nitrogen from vegetative biomass, which can be comparable to cover crop nitrogen delivery if the forage is allowed to regenerate between cuttings. In organic farming, cereal and other non-legume crops in rotation can help create soil organic matter, which is an essential nutrient store. Root architecture is critical for long-term crop rotation. Long-term planning and a broad mix of cultural practices and inputs are required for nutrient management on organic farms.

Biofertilizers

Bio-fertilizer is a product that contains living microorganisms that colonize the rhizosphere or the interior of the plant and encourage development when applied to seed, plant surfaces, or soil. Bio-fertilizers improve soil fertility by providing nutrients through natural processes such as nitrogen fixation and phosphorus solubilization and stimulating plant growth by adding growth-promoting chemicals.

The extensive use of synthetic fertilizers has led to soil pollution and contamination, which in turn has polluted water basins, destroyed beneficial microorganisms and insects, and made crops more prone to diseases. This has also reduced soil fertility. The following points highlight major concerns:

• Demand vs. Availability: By 2020, to achieve the targeted production of 321 million tons of food grain, the nutrient requirement was estimated to be 28.8 million tons. However, the availability was projected to be only 21.6 million tons, resulting in a deficit of about 7.2 million tons.
• Rising Costs: Depleting fossil fuels and the increasing cost of fertilizers are becoming unaffordable for small and marginal farmers.
• Soil Fertility: There is a widening gap between nutrient removal and supply, leading to depleting soil fertility.
• Environmental Hazards: There are growing concerns about the environmental hazards associated with synthetic fertilizers.

Biofertilizers offer a sustainable alternative. They include:

• Nitrogen fixers, such as Rhizobium, Azospirillum, Azotobacter, Blue-Green Algae (BGA), and Azolla.
• Phosphate absorbers, Such as mycorrhizae.
• Zinc solubilizers, that help in nutrient mobilization

Using biofertilizers can improve soil health and reduce the dependency on synthetic fertilizers, promoting more sustainable agricultural practices (Mahdi et al., 2010).

Green Manure:

After pasture, green manures are the next most important source of nitrogen. Green manure is a crop that will develop quickly between two cash crops. When incorporated into the soil or left to die on the soil surface, it will provide nitrogen and other nutrients to the next crop, increase the soil's organic material and water-holding capacity, and reduce weed population. A typical green manure consists of a 50:50 mixture of cereal and legumes. This will produce the maximum biomass and will be able to fix more nitrogen than a pure legume stand. This is because the grain absorbs a large amount of soil nitrogen during growth, reducing soil-accessible nitrogen and allowing the legume to fix more nitrogen. When there is abundant nitrogen in the soil, legumes reduce N fixation and instead utilize soil nitrogen because fixation demands a lot of energy and minerals that may be used elsewhere. Green manures can be planted at any time of year, but because cash crops occupy the fields during the summer in most cropping systems, the main usage of green manures is during the winter. Often, fast-growing species like Phacelia (Phacelia tanacetifolia) or brassicas like mustard are employed (Brassica juncea). (Barry et al., 2008)

References

• Faux, A.-M., Decruyenaere, V., Guillaume, M., & Stilmant, D. (2021). Feed autonomy in organic cattle farming systems: A necessary but not sufficient lever to be activated for economic efficiency. Organic Agriculture. https://doi.org/10.1007/s13165-021-00372-0
• Barry, P., Merfield, C., Advisory, T. M., & Cork, C. (2008). Nutrient management on organic farms. https://www.teagasc.ie/media/website/publications/2000/NutrientManagementonOrganicFarms24-11-08.pdf
• Mahdi, S. S., Hassan, G. I., Samoon, S. A., Rather, H. A., Dar, S. A., & Zehra, B. (2010). Bio-fertilizers in organic agriculture.
• Thompson, A. A. (2021). NebGuide. June, 1–7.
• Briggs, S., Cuttle, S., Goodlass, G., Hatch, D., King, J., Roderick, S., & Shepherd, M. (2015). Soil nitrogen building crops in organic farming. ABACUS Ltd., IGER, ADAS & Duchy College, UK.
• Nesme, T., Colomb, B., Hinsinger, P., & Watson, C. A. (2014). Soil phosphorus management in organic cropping systems: From current practices to avenues for a more efficient use of P resources. In Organic farming, prototype for sustainable agricultures: Prototype for sustainable agricultures (pp. 23–45). https://doi.org/10.1007/978-94-007-7927-3_2
• Mikkelsen, R. L. (2007). Managing potassium for organic crop production. HortTechnology, 17(4), 455-460.
• Baldwin, K. R., & Greenfield, J. T. (2009). Composting on organic farms. Center for Environmental Farming Systems, New York, NY, USA.
• Hue, N. V., & Silva, J. A. (2000). Organic soil amendments for sustainable agriculture: organic sources of nitrogen, phosphorus, and potassium. Plant nutrient management in Hawaii’s soils, approaches for tropical and subtropical agriculture. College of Tropical Agriculture and Human Resources, University of Hawaii, Manoa, 133-144.