Nitrogen is an essential element required for successful plant growth. Although inorganic nitrogen compounds (i.e., NH4+, NO2‒, and NO3‒) account for less than 5% of the total nitrogen in soil, they are the main form of the element absorbed by most plants. Inorganic and organic fertilizers are applied to maintain the nutritional condition of different cropping systems. For an organic agricultural system, continuous application of manure increases the nitrogen (N), phosphorus (P), potassium (K), calcium, and magnesium content in soil. Once organic fertilizers are applied to soils and mineralization begins, inorganic nitrogen is released and absorbed by plants. However, the rate of mineralization is controlled by several factors, including agricultural management, microorganism, soil properties, temperature, and water content, as well as the type of organic fertilizer. Many models have been developed to predict the release of nitrogen in applied organic fertilizers.
With the increased cost of nitrogen (N) fertilizer and concerns about the adverse environmental impacts of N losses, there is great interest in fine-tuning N fertilizer management. The goal is to match application source, rate, timing and method to supplement on-farm sources of N (e.g., manure, soil organic N, sod, legume cover crops) to meet crop needs and achieve optimum levels of N use efficiency. Optimum N fertilizer management requires an understanding of the different N fertilizers.
