Nitrogen Nutrition of Crop Plants: Soil Nitrogen Vis-à-Vis Fertilizer Nitrogen

In unmanaged ecosystems, soil nitrogen (N) released through mineralization of organic matter constitutes the source of N for the plants. In agro-ecosystems, N is applied additionally as mineral or organic fertilizers in order to compensate N which is removed with products. Adequate and timely application of fertilizer N as dictated that by contribution of soil N to crop production is important for minimizing production costs from overuse of N fertilizer and for reducing possible environmental impacts. Using 15N-labelled fertilizers, it has now been convincingly proved that majority of the plant N comes from the soil N. Thus, soil N plays a vital role in supplying N to crop plants and dictates the efficiency of applied fertilizer N. Size of available N pool, though relatively small as compared to total soil N, throughout the crop growth season determines whether crop gets adequate N nutrition or N is lost from the soil-plant system. As fertilizer N contributes directly to available N pool and by N substitution to the soil organic matter pool, N management at that point following the principles of synchrony between crop N need and application of N through soil and fertilizer N can lead to high fertilizer NUE (nitrogen use efficiency). Evaluation of site-based N management in cereals using gadgets like chlorophyll meter, leaf colour chart or optical sensors or OTG (on the go) crop sensing spreaders revealed that same yields can be achieved with less N fertilizer applied but with enhanced fertilizer NUE and diminished losses of N to the environment