Effects of Different Irrigation and Nitrogen Supply Levels on Nitrate-N Dynamics in a Recently Reclaimed Sandy Farmland in Heihe River Basin
灌溉与施氮对黑河中游新垦沙地农田土壤硝态氮动态的影响

Improper nitrogen (N) and irrigation management are major causes leading to deterioration in water environmental quality in the middle reaches of Heihe River basin. A controlled experimental study of different irrigation and N supply levels was therefore conducted in the Linze Inland River Basin Research Station, Chinese Academy of Sciences, to determine the influences of N addition and irrigation regime on the dynamics of nitrate-N (NO3--N) distribution in soil profiles over the growing season of spring wheat. The experiment employed a completely randomized block split-plot design, with irrigation treatments 0.6, 0.8, 1.0 of the estimated evapotranspiration (ET), denoting I0.6, I0.8 and I1.0 respectively] and N addition treatments 0, 140, 221, 300 kg.hm-2, denoting N0, N140, N221 and N300 respectively] as the main-plot and split-plot, respectively. Our results show that the rate of N is the key factor in influencing NO3--N content and its leaching. The content of NO3--N in the 0-200 cm soil profiles was found to increase with increased N rates, and in particular this increase was more pronounced when the N rates ranged between 221 kg.hm-2 and 300 kg.hm-2. In addition, NO3--N leaching is relatively less apparent at the N rates in the range of 0-140 kg.hm-2, but this effect became significant when the N rates exceeded 140 kg.hm-2. Our results also show that NO3--N contents were generally higher at the anthesis stage than at the harvest stage within the same soil layer. The observed differences in NO3--N contents between the irrigation treatments of I0.6, I0.8 and I1.0 were insignificant across N rates. This finding suggests that N addition treatments may have greater impacts on NO3--N leaching than irrigation treatments. Although the among-irrigation differences of NO3--N contents within the same soil layer varied with N level, there was a tendency that NO3--N content of I1.0 treatment was significantly lower than that of I0.8, and that of I06 irrigation treatment in the soil layer with significant differences in N contents. This result suggests declined NO3--N leaching with decreased irrigation levels.