A nitrogen index for improving nutrient management within commercial Mexican dairy operations

Some intensive dairy operations in Mexico are contributing to large, negative environmental impacts, especially in regions dominated by high concentrations of animals. Excessive manure inputs plus additional nitrogen (N) fertilizer has, in some cases, resulted in background nitrate–nitrogen (NO3–N) levels in irrigation water that are so high, it is not safe for human consumption. One reason is that commercial farmers in this region are currently not using any method to rapidly calculate N budgets based on their practices, N inputs and/or crop N uptake. The Nitrogen Index, a quick tool that can be used to conduct an assessment within a few minutes, was developed for Mexico, but needed further testing under commercial field operations. We conducted studies in 2010 and 2011 and collected soil and crop information from several commercial farming operations to test the tool. The index accurately assessed (P<0.0001) residual soil nitrate after harvesting corn (Zea mays L.) and oats (Avena sativa L.); and also accurately assessed the N uptake of these crops (P<0.01). The Mexico N Index is a tool that can be used to quickly conduct N balances, show when N is being over-applied, and help reduce over-application, thus reducing N losses to the environment and improving management of dairy forage systems in Mexico.