Use of the Nitrogen Index to assess nitrate leaching and water drainage from plastic-mulched horticultural cropping systems of Florida

Water quality in Florida is significantly impacted by nitrate (NO3-N) leaching losses from agriculture in a large part of the state. Horticultural crops are planted across large areas of Florida on coarse sandy soils with low soil water retention and soil organic matter, increasing the potential for NO3-N leaching. Nitrate leaching losses from the root zone of vegetable cropping systems can negatively impact groundwater. New tools such as the Nitrogen Index (N-Index) are able to quickly assess N use efficiency and losses via NO3-N leaching from agricultural systems. Furthermore, the N-Index provides technical information about N losses pathways tied to agricultural management practices with a great level of confidence; this information has been used by researchers, growers and policymakers as a decision support system. However, the current version of the N-Index that has been used for different field crops has not been calibrated to be used in plastic-mulched horticultural cropping systems. The aim of this work was to calibrate and validate the N-Index for plastic-mulched horticultural cropping systems of Florida. This study found that the N-Index tool accurately identified and ranked the risk of N losses in the evaluated horticultural systems. The N-Index was calibrated for Florida's plastic-mulched horticultural cropping systems using a sensitivity analysis. The adjusted N-Index was validated using compiled data of vegetables grown under plastic mulching systems during three consecutive seasons. Results from these studies suggest that the N-Index can be an easy-to-use tool capable of assessing nitrogen management practices for vegetable systems. The tool can be used to guide nutrient managers in the implementation of best nitrogen management practices that could contribute to reduced NO3-N leaching losses from vegetable systems in Florida, contributing to a smaller environmental footprint and conservation of water quality.