Rainfall amount and distribution regulate DMPP effects on nitrous oxide emissions under semiarid Mediterranean conditions

Nitrogen fertilizer application timing and the use of nitrification inhibitors are currently promoted as agronomic practices with potential to reduce nitrous oxide (N2O) emissions. However, the efficacy of these practices is to a large extent regulated by weather variability, particularly rainfall and temperature. This is primarily the case for rainfed crops under semiarid Mediterranean climate, where large fluctuations occur in the amount and frequency of rainfall from year to year. In this 3-year field experiment, we explored the potential of fertilizer application timing and a nitrification inhibitor (3,4-dimethyl pyrazole phosphate; DMPP) to achieve low N2O, for a rainfed barely (Hordeum vulgare L. cv Pedrezuela) crop under a semiarid Mediterranean climate. Five fertilizer management practices were tested: split fertilizer application at planting and at tillering with (1) or without DMPP (2); the same split fertilizations but applying DMPP only at tillering (3); and single fertilizer application al tillering with (4) or without DMPP (5). During the dry conditions of year 1, the application of DMPP reduced N2O emissions (up to 72%) whereas timing of fertilizer application had no effect. Conversely, under the wet conditions of year 2 the effect of DMPP was suppressed but fertilizer timing was successful diminishing N2O, with lower emissions measured with single fertilizer application at tillering. In year 3, where rainfall distribution was remarkably erratic, N2O emissions were mitigated by both DMPP and single fertilizer applications. Overall, our results show that DMPP offers an opportunity for N2O abatement in semiarid soils under Mediterranean environments. The low moisture content of these soils during long periods favors nitrification; by inhibiting this process, products such as DMPP are able to achieve large N2O reductions. Although single fertilizer application at tillering as opposed to the traditional split application at planting and tillering may provide a management opportunity for N2O mitigation, we also found that this practice may lead to yield reductions in years with sufficient rainfall in spring. Therefore, general implementation of this practice should not be encouraged.