Strategies to reduce gaseous emissions of nitrogen from irrigated agriculture

Fertilizer nitrogen (N) is not used efficiently in irrigation agriculture because much of the N applied is lost from the plant-soil system by emission of gaseous compounds to the atmosphere. Nitrogen may be emitted by ammonia volatilization, and as nitrous oxide, nitric oxide and dinitrogen during nitrification, biological denitrification and chemodenitrification. Nitrogen emitted to the atmosphere as ammonia may be returned to the biosphere and recycled thus adding to the nitrous oxide and nitric oxide burden in the atmosphere. Thus ammonia volatilization needs to be controlled as well as nitrification-denitrification to limit emission of nitrogen oxides. Many approaches have been suggested for controlling losses of fertilizer N including optimal use of fertilizer form, rate and method of application, matching N supply with demand, supplying fertilizer in the irrigation water, applying fertilizer to the plant rather than the soil, and use of slow-release fertilizers. While these techniques have the potential to increase the effectiveness of the applied N none of them have a large impact on gaseous loss of N. However, the results of recent experiments in tropical and temperate regions with flooded rice, and irrigated cotton, wheat and maize show that use of newly developed urease and nitrification inhibitors has the capacity to prevent loss of N and increase the yield of crops.