Nitrogen Hotspots on the Farm—A Practice-Oriented Approach

The proactive management of nitrogen (N) on a farm is the best way to protect the environment against N pollution. The farm is the basic business unit, where simple and low-cost methods of identifying and ameliorating weaknesses (nitrogen hotspots) in the N-flow chain can be applied. The basis for the effective use of mineral N fertilizers (Nf) is the farmer’s knowledge of the farm’s own N resources, their quantity, and the potential availability for growing crops. These resources include both primary sources of N (N2 fixed by legumes) and those that are recyclable, which include crop byproducts and manure. On the other hand, crop requirements must be accurately quantified to exploit the yield potential of the crop varieties grown on the farm. The basic challenge for the farmer is to maximize the use efficiency of the N resources. In this regard, the farmer has two diagnostic tools available to recognize nitrogen hotspots and to quantify N resources. These are (1) the N balance method (difference between the N inputs and outputs), which allows for a surplus or deficiencies in the N-flow between farm units (fields, livestock housing) to be identified, and (2) the nitrogen gap, which is based on the amount of Nf applied and the yield of a given crop. It is possible to calculate the maximum attainable yield as well as identify the fields on the farm that require a correction of N management.