Comparison of different approaches for optimizing nitrogen management in sprinkler-irrigated maize

The gap between scientifically sound nitrogen (N) fertilizer application rates and the actual rates used by farmers in maize is still significant. The improvement of nitrogen use efficiency in such a highly N-demanding crop is necessary to decrease the negative effects of N fertilization. The objective was to compare the performance of different N management treatments in maize grown under semiarid Mediterranean sprinkler-irrigated conditions to the standard farmer practice. We compared an agronomically sound fixed rate of N fertilizer (FR) with a variable N rate obtained based on a soil mineral balance at pre-planting (SB) or based on a portable chlorophyll meter readings (CM) made just before tasseling. Additional treatments were a N control, without fertilizer (T0), and a non-limiting N (NL) treatment wich was typical of the current farmer practice. The study was replicated at 5 sites in one-year experiments and under 3 pre-planting soil mineral nitrogen environments (SMN, Low, Medium, and High). The results demonstrate the potential to reduce N rates from zero to 236 kg N ha-1 compared to the NL in irrigated maize fields without compromising yields in most of the situations with a subsequent increase of NUE. Averaging over sites, the use of fine-tuning N fertilizer strategies that considered field-specific conditions (SB and CM) reduced N rates (38 %) compared to the reductions under the FR strategy (26 %) relative to the NL conditions, which is the treatment closest to a typical farmer`s application rate