A controlled study of irrigation and nitrogen (N) supply was conducted in the Hexi oasis to investigate the effects of different irrigation and N supply levels on soil organic carbon(OC),soil total nitrogen(TN),soil carbon and nitrogen ratio (OC/TN) of spring wheat on no-tillage farmland with standing stubble.With an increase in N supply rate,TN and OC contents considerably increased in soils.However,when N supply rates were higher than 140 kg N/ha,TN did not continuously increase with the increase in N supply rate,and OC even showed a decreasing trend.Irrespective of nitrogen levels,with an increase in irrigation level,TN and OC contents initially increased but then decreased in soils.An appropriate amount of irrigation (20％ water-saving irrigation) promoted the mineralization rate of soil nitrogen and carbon,thus increasing the TN and OC contents.However,a smaller amount of,or excessive,irrigation reduced soil nitrogen and carbon mineralization rates,and increase soil nitrogen and carbon losses.The highest TN (0.9 g/kg) and OC (14.22 g/kg) were measured under 20％ water-saving irrigation.When the N supply rate was 221 kg N/ha,the grain yield reached a maximum (6 365 kg/ha) irrespective of the irrigation levels but the grain yield of spring wheat increased with an increase in irrigation level.%在甘肃省石羊河流域绿洲灌区,研究不同灌溉量和施氮量对留茬免耕春小麦收后0～30 cm土层土壤有机碳、土壤全氮和土壤碳氮比的影响.结果表明,在0～140 kg/hm2施氮范围,土壤全氮和有机碳含量增施氮肥均明显增加,当施氮量超过140 kg/hm2时,土壤有机碳随施氮量增加而降低,土壤全氮含量无明显变化.就平均施氮水平而言,土壤全氮和有机碳含量随灌溉量增加呈先升高后下降的趋势,适量灌溉(节水20％灌溉)促进土壤氮和碳的矿化速率,从而增加全氮和有机碳含量,但少量或过量灌溉降低土壤氮和碳的矿化速率,同时增加土壤氮和碳的损失,导致节水20％灌溉的土壤全氮含量(0.9 g/kg)和有机碳含量(14.22 g/kg)最高.就各灌溉水平平均值而言,当施氮达到221 kg/hm2,春小麦籽粒产量(6 365 kg/hm2)达到最大值,春小麦籽粒产量随灌溉量增加而增加.
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