enrich soil as a green manure through nitrogen fixation from the atmosphere; as well as phosphorus (through nutrient mobilization) content of soils. Comparison Nutrient density In general, the nutrients in organic fertilizer are both more diluted and also much less readily available to plants. This may be however desired as a form of slow-release fertilizer containing insoluble nitrogen. By their nature, organic fertilizers increase physical and biological nutrient storage mechanisms in soils, mitigating risks of over-fertilization. Organic fertilizer nutrient content, solubility, and nutrient release rates are typically much lower than mineral (inorganic) fertilizers. A University of North Carolina study found that potential mineralizable nitrogen (PMN) in the soil was 182–285% higher in organic mulched systems than in the synthetics control. There do exist 'fast-release' organic fertilizers with a risk of fertilizer burn. These include uncomposted animal manures, fish emulsion, blood meal, and urine. Composting converts nitrogen in these sources into more stable forms (with some loss). Soil biology Organic fertilizers have been known to improve biodiversity (soil life) and long-term productivity of soil, and may prove a large depository for excess carbon dioxide. Organic nutrients increase the abundance of soil organisms by providing organic matter and micronutrients for organismal relationships such as fungal mycorrhiza, (which aid plants in absorbing nutrients), and can drastically reduce external inputs of pesticides, energy and fertilizer, at the cost of decreased yield. Consistency Organic fertilizers from composts and other sources can be quite variable from one batch to the next. Without batch testing, amounts of applied nutrient cannot be precisely known. Nevertheless, one or more studies have shown they are at least as effective as chemical fertilizers over longer periods of use. See also Biosecurity Compost Controlled release fertiliser Cover crop Fertilizer Food additive Grasscycling Manure Vermicompost See also Seaweed fertilizer Biofertilizer Organic hydroponic solutions Reuse of excreta References Organic gardening Horticulture