QUANTIFYING NITRATE LEACHING IN IRRIGATED WHEAT WITH DIFFERENT NITROGEN FERTILIZATION STRATEGIES IN AN ALFISOL

Consumption of water contaminated with nitrates is associated with important health effects such as methemoglobinemia and gastric cancer. Intensive agriculture, which uses large quantities of N fertilizer, is the main source of nitrates in water systems. There are several strategies to reduce leaching and increase Nitrogen Use Efficiency (NUE). An experiment was conducted with spring wheat (Triticum aestivum L.) under sprinkler irrigation (center pivot) to determine if adjusted N applications using precision agriculture tools and plant demand resulted in a lower groundwater nitrate load. Evaluated treatments were: producer fertilization (Pr), precision agriculture (Pa), chlorophyll meter (Sm), and control without N (W/N). The ceramic capsule methodology was used to evaluate N leaching losses that were sampled after each irrigation (six) and drainage water was also estimated. Differences among treatments in terms of N loss and grain yield were not significant (p > 0.05). However, N balance showed significant differences (p < 0.01) in soil residual N among treatments. A regression between applied and residual soil N after harvest showed that N, applied as fertilizer, explained 98% of residual soil N variation, which would probably be leached in the following winter since the soil would be bare. It was concluded that NUE can be improved to result in a lower environmental load by using precision agriculture tools and considering plant N demand.