A new Nitrogen Index to evaluate nitrogen losses in intensive forage systems in Mexico

Although nitrogen inputs to agricultural fields are necessary for global food sustainability, they present a major nutrient management challenge, because nitrogen inputs can increase nitrogen losses to the environment, which can negatively impact water quality across key surface and groundwater resources. The need to evaluate the potential risk of nitrogen losses for a given forage type, management scenario, and field quickly and easily can be met with new tools that assist in environmental risk assessment. An example is the Mexico Nitrogen Index: this new tool aims to help its users quickly evaluate the risk of nitrogen loss for a given field under a given set of management practices. The objective of this study was to evaluate the accuracy of the Mexico Nitrogen Index in ranking the risk of nitrogen loss for a given field under a given set of management practices. To perform this evaluation, data for several different management scenarios were collected and entered into the Mexico Nitrogen Index. The capability of the Index to assess the fate and transport of nitrogen and to rank the risk of nitrogen loss was evaluated by comparing predicted soil residual nitrate and forage nitrogen uptake with observed values. Nitrogen fate and transport were accurately predicted under many different scenarios (P < 0.001); for example, the Index was successful in accurately predicting higher potential risk for nitrogen loss for scenarios with excessive nitrogen applications. It was concluded that the Mexico Nitrogen Index can accurately perform these risk assessments and that it has the potential to facilitate communication between scientists, extension personnel and farmers about the effects different management practices may have on nitrogen losses.

► The Mexico N Index can be used to help preserve water quality in Mexico.
► Average N inputs in the region are higher than needed, affecting the environment.
► The Mexico N Index can assist its users in determining how much N to apply.
► The index identifies forage management changes that can increase sustainability.
► The Mexico N Index can be an informative and educational tool.