Managing Risk Through Efficient N Use in Field Crops

Opportunities for reducing N imports (e.g. feeds and fertilizers) and making better use of on-farm N supplies (e.g. manure, soils, and crops) require a team approach across the soil/crop, feed storage, herd, and manure systems on the farm. In many dairy farm mass balance studies, purchased feeds, alone, account for 60-90% of the imported N, with fertilizers and N fixation by legumes responsible for the remainder of the N imports (Cerosaletti et al., 2003; Klausner, 1993; Klausner et al., 1998; Tylutki and Fox, 1997). This section will focus on N losses and approaches to reduce N losses from the crops enterprise/landbase, the initial focus of many nutrient management regulations, such as CAFO.

Nitrogen losses from farm fields are most likely to occur when N is present in excess of crop requirements and/or at a time of the year of low crop nutrient uptake. Manure and fertilizer application methods can also influence nitrogen losses, via ammonia volatilization. The following pages detail N losses to watercourses and the atmosphere and provide approaches to make efficient use of N through precision forage management.