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Organic fertilizer refers to those organic amendments applied to soils, other than direct deposition of excreta by grazing animals, and includes animal manure, sewage sludge and compost, along with rendering waste, guano, brewery waste, digestate and other bio-wastes. They can contribute large amounts of nutrients to soils, for example, estimates of the potential amount of cattle manure produced in different countries show a range between 8,304,000.00 (UK) and 77,094,000.00 Mg y−1 (US) (Thangarajan et al., 2013). They are favored from the farmer's point of view due to their potential to increase soil fertility and productivity but can be vulnerable to nutrient losses to water and the atmosphere due to priming effects and their susceptibility to promote nitrification and denitrification. Moreover, there is a concern about the potential risk of toxic elements inputs (e.g., heavy metals) mainly under intense rainfall events when organic amendments are applied. A rigorous regulation should consider the field conditions to ensure a safe application and provide guidance. For instance, grazing is not allowed for 3 weeks after spreading sewage sludge in the UK, and there is a soil testing requirement. The method of application of organic amendments influences the form of nitrogen lost, for example, trailing shoe, splash plate.