Nitrogen and water use efficiency under rain-fed potato agriculture: an experimental study

Water and nitrogen (N) use efficiency is an important focus in agricultural research. Moreover, the estimation of N-uptake efficiency of inorganic fertilizer application is a key aspect to develop best management practices (BMPs). The general objective of this study is to assess potato nitrogen and water use efficiencies for different inorganic nitrogen fertilization levels in the Peruvian Central Andes (Mantaro Valley). A further objective was to evaluate the seasonal change of potato biomass and N-uptake. During the 2015-2016 rainy cropping season, one experiment with different N fertilization (0, 100, 200, 300 and 400 kg N ha‑1) was established on a clay loam soil. Destructive measurements were periodically performed in order to calculate leaf area index (LAI), biomass and N-uptake dynamics. Actual total evapotranspiration was adjusted to LAI measurements reaching 343, 436, 426, 438 and 438 mm, not representing a limiting factor in relation to the water supply (462 mm). An improvement of aboveground biomass from 51.2 (100 kg N ha(‑1)) to 61.8 t ha(‑1) (400 kg N ha(‑1)) in relation to N fertilization was achieved. Fresh tuber yield (13.6, 41.9, 47.2, 55.0 and 52.3 t ha(‑1) was significantly enhanced by N fertilization, reaching optimal production with 200-300 kg N ha(‑1). Similarly, N treatments markedly improved N-agronomic efficiency (NAE; 31.9, 26.8, 24.2 and 21.9 kg kg(‑1)), N-apparent recovery efficiency (NARE; 50.5, 48.1, 55.1 and 50.7%) and N-harvest index (NHI; 72.9, 78.8, 71.7 and 73.8%). A not obvious increasing trend in function of the N treatments was obtained for NARE and NHI due to the combined effect of N-uptake, N-assimilation and N-losses. However, 200 and 300 kg N ha(‑1) represented the most efficient treatments for NARE and NHI, respectively. Water use efficiency was indirectly enhanced from 8.45 kg m‑3 (100 kg N ha(‑1)) to 15.28 kg m‑3 (400 kg N ha(‑1)). Future developments of soil-crop BMPs under rain-fed conditions should focus on optimizal time and dosing of N application under integrated approaches to enhance N-use efficiency indices under local conditions.