| Effects of different water-nitrogen conditions on yield and water and nitrogen use efficiency were studied
by field experiment in marginal oasis regions of Heihe River Basin. The results showed that:Compared with that of high water and fertilizer (W1F1)，the other treatments decreased plant height, increased root-shoot ratio and the root depth(except of W1F2)，among which the treatment of low water and nitrogen (W3F2) caused most remarkable change in plant height, root-shoot ratio and the root depth, and the plant height decreased by 14.1%, the root depth and root-shoot ratio increased by 13.3% and 88.9%, respectively. The above-ground biomass yield increased with nitrogen amount increas-ing in same irrigation amount，but the effect on production increase was more significant in low irigation amount with ni-trogen amount increasing; it also increased with irrigation amount increasing in same nitrogen amount，but the effect on production increase was the best in low fertilizer condition along with irigation amount increasing. Water use fficiency presented decreasing trend with the increase of irrigation amount in two nitrogen conditions, but nitrogen use efficiency showed increasing trend. The above ground biomass yield and total biomass yield in high water and fertilizer were maxi-mum，and the values were
87 t/ hm2 and 99 t/hm2, respectively . The low water and fertilizer were opposite to it, and the values were 73 t/hm2 and 90 t/ hm2，but they had no significant difference, while the nitrogen use eficiency in W3F2 in-creased by 13.2% compared with W1F1. All these indicated that the high biomass yield and high water and nitrogen use efficiency could be acquired in the marginal oasis regions through adopting irmigation amount of 7 760 m3/hm2，accompa-nied by nitrogen fertilizer amount of 220 kg/hm2. |