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 N-0, the increases of fertilizer N loss, in N-79, N-140, N-221 and N-300 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.