灌溉与施氮对黑河中游新垦农田土壤硝态氮积累及氮素利用率的影响

Effects of different irrigation and N supply levels on NO_3^--N accumulation and N use efficiency on a recently reclaimed sandy farmland in Heihe River basin

通过田间试验系统研究了黑河中游边缘绿洲区新垦沙地农田不同灌溉与施氮量(0、140、221kgNhm-2和300kgNhm-2,分别为N0、N140、N221和N300)对2m土层土壤硝态氮的积累和分布、春小麦产量、植株吸氮量及氮肥利用效率的影响。结果表明:在378～504mm灌溉水平下,当施氮量大于221kghm-2(超过作物吸氮量)时会导致收获期NO3--N在根层土壤剖面的显著积累(50～140kghm-2);在灌溉量为630mm时,收获期各处理根层土壤NO3--N的积累量(25～47kghm-2)要低于播种前(58～63kghm-2)。当施氮量超过221kghm-2时,春小麦籽粒产量、地上干物质量、植株吸氮量、氮肥表观利用率及生理效率均不再显著增加,N221与N0、N140、N300相比,其籽粒产量分别提高46.7%、41.3%与9.5%,地上干物质量分别提高31.3%、25.2%与3.5%。灌溉水生产力的变化介于2.0～5.3kghm-2mm-1,氮肥生产力的变化介于6.3～10.8kgkg-1。研究还表明,灌溉与施氮对土壤贮水量的影响不显著,在378mm低灌水量时,小麦产量与地上干物质量无显著的影响,这说明在黑河流域新垦沙地农田系统低灌溉(灌溉量378mm)与221kghm-2施氮是最优的水肥耦合组合,因为在此管理模式下不仅可以获得相对较高的产量,而且灌溉水和氮素的利用效率较高,硝态氮的积累量较小。

In the middle reaches of the Heihe River basin, environmental deterioration in agricultural ecosystems caused by excessive nitrogen （N） supply and high irrigation rate has received much attention in recent years. A field experiment was designed to investigate the effects of different irrigation and N supply levels on soil grain yield, N uptake and N use efficiency in a recently reclaimed sandy farmland NO3^- -N accumulation and distribution, system in the Heihe River basin. The experiment followed a completely random split-plot design, taking the irrigation treatment as main-plot （with three levels of 378, 504 mm, and 630 mm for the whole growing season） and N supply treatment as split-plot （with four levels of 0, 140, 221, 300 kg hm^-2 ; denoting N0, N140, N221, andN300, respectively）. Our results showed that grain yields, above-ground dry-matter biomass, plant N in above-ground dry-matter biomass, apparent N recovery fraction, and physiological efficiency did not increase significantly with increasing N supply rates when N supply rate exceeded 221 kg hm^-2. Average grain yields in N221 were found to be 46.7%, 41.3% and 9.5% higher than N0, N140 and N300, respectively, whereas average above-ground dry-matter biomasses in N221 were 31.3%, 25.2% and 3.5% higher than No, N140and N300, respectively. Under the rates of irrigation between 378 mm and 504 mm, a rate of N supply over 221 kg hm^-2 resulted in a significant accumulation of NO3^- -N （from 50 kg hm^-2 to 140 kg hm^-2） in the 0 -200 cm soil profile. Under the rate of irrigation of 630 mm, NO3^- -N accumulation in the 0 -200 cm soil profile ranged from 25 kg hm^-2 to 47 kg hm^-2at harvest stage, being lower than that （58 kg hm^-2 to 63 kg hm^-2） at sowing. Overall, N fertilizer productivity varied from 6.3 kg kg^-1 to 10.8 kg kg^-1 , while irrigation water productivity varied from 2.0 kg hm^-2mm^-1 to 5.3 kg hm^ -2mm^ -1 in this recently reclaimed sandy farmland system. However, we found that neither irrigation nor nitrogen supply had a significant influence on soil water storage. The results of this study suggest that the combination of irrigation and nitrogen supply of 378 mm and 221 kg N hm^-2may be the best management strategy because of its relatively higher grain yield, higher irrigation water productivity, and higher N use efficiency, as well as lower NO3^- -N accumulation.