[Effects of different irrigation and nitrogen supply levels on nitrate-N dynamics in a recently reclaimed sandy farmland in Heihe River basin].

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 x hm(-2), denoting N0, N140, N221 and N30 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 x hm(-2) and 300 kg x hm(-2). In addition, NO3(-) -N leaching is relatively less apparent at the N rates in the range of 0-140 kg x hm(-2), but this effect became significant when the N rates exceeded 140 kg x 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.