Effects of irrigation and nitrogen application rates on nitrate nitrogen distribution and fertilizer nitrogen loss, wheat yield and nitrogen uptake on a recently reclaimed sandy farmland

Monitoring of drinking water has shown an increase in nitrate-nitrogen (NO 3 − -N) concentration in groundwater in some areas of the Heihe River Basin, Northwest China. A combination of careful irrigation and nitrogen (N) management is needed to improve N uptake efficiency and to minimize fertilizer N loss. A 2-year experiment investigated the effects of different irrigation and N application rates on soil NO 3 − -N distribution and fertilizer N loss, wheat grain yield and N uptake on recently reclaimed sandy farmland. The experiment followed a completely randomized split-plot design, taking flood irrigation (0.6, 0.8 and 1.0 of the estimated evapotranspiration) as main plot treatment and N-supply as split-plot treatment (with five levels of 0, 79, 140, 221, 300 kg N ha−1). Fertilizer N loss was calculated according to N balance equation. Our results showed that, under deficit irrigation conditions, N fertilizer application at a rate of 300 kg ha−1 promoted NO 3 − -N concentration in 0–200 cm depth soil profiles, and treatments with 221 kg N ha−1 also increased soil NO 3 − -N concentrations only in the surface layers. Fertilizer N rates of 70 and 140 kg ha−1 did not increase NO 3 − -N concentration in the 0–200 cm soil profile remaining after the spring wheat growing season. The amount of residual NO 3 − -N in soil profiles decreased with the amount of irrigation. Compared with N0, the increases of fertilizer N loss, in N79, N140, N221 and N300 respectively, were 59.9, 104.6, 143.5 and 210.6 kg ha−1 over 2 years. Under these experimental conditions, a N rate of 221 kg ha−1 obtained the highest values of grain yield (2775 kg ha−1), above-ground dry matter (5310 kg ha−1) and plant N uptake (103.8 kg ha−1) over 2 years. The results clearly showed that the relative high grain yield and irrigation water productivity, and relative low N loss were achieved with application of 221 kg N ha−1 and low irrigation, the recommendation should be for those farmers who use the upper range of the recommended 150–400 kg N ha−1, that they can save about 45% of their N and 40% of their irrigation water application.