Effect of long-term fertilizer application on soil productivity and nitrate accumulation in Gansu Oasis

chinois. 在甘肃河西绿洲灌漠土上进行的长期定位试验表明，连续20年不施用任何肥料，导致农田土壤生产能力严重衰退。2001年不施肥的小麦产量仅是试验开始时（1982年）的25.7%，2000年的玉米产量为1984年的28.2%。肥料是影响农田土壤生产力的重要因素，不同肥料的影响程度依次是：氮肥＞有机肥＞磷肥＞钾肥，其平均增产率分别为36.5%、27.3%、24.7%和2.9%。随着试验年限的延长，不施任何肥料的对照产量持续降低，故氮肥的增产效果增加；磷肥增产效果比较平稳；钾肥在试验开始后最初6年（1982～1987年）无显著增产效应，中期具有一定的增产作用（1988～1992年），后期8年（1993～2001年）显著增产。施用有机肥的增产作用随着试验延续呈逐步增加的趋势，表明长期施用有机肥具有明显的残效叠加效应。不同施肥处理对土壤中NO-3-N的积累与分布有显著的影响。施用化肥的处理（NP和NPK）导致NO3--N在土壤剖面中大量积累，尤其是在20～140 cm土层。化肥与有机肥配合施用(MNP 和 MNPK) NO3--N在土壤剖面中的积累显著低于化肥处理。长期连续施用化肥和有机肥均导致土壤剖面中硝态氮的积累；与化肥相比，有机肥导致更深土壤剖面（140～180 cm）中硝态氮的积累，因此，长期有机无机肥配合施用可显著增加绿洲农田土壤生产力，维持和提高土壤质量，但从持续农业发展及保护生态环境等方面考虑，应适当降低施肥量。

anglais. A long-term (1982-2001) field experiment was conducted on a calcareous soil at Zhangye, Gansu under wheat (Triticum aestivum L.)-wheat(Triticum aestivum L.)-corn (Zea mays L.) rotation system in order to determine the effects of long-term fertilization on crop yield, content and accumulation of nitrate-N in soil profiles. Twenty-four plots in a split-plot include eight treatments [nitrogen (N), phosphorus (P), potassium (K) and farmyard manure (M) application] and 3 replicates were designed. Main treatments were M and no M, and the sub-treatments were no-fertilizer (CK), N, NP and NPK. In P and K were part of treatments, their ratio to N was 1Ns0.22Ps0.42K. All M, P and K fertilizers were applied as the basal dressing. The crops were harvested for grain yield in all years and for straw yields from 1988 to 1997. After crop harvest in 2000, the soil was sampled from the 0-20, 20-60, 60-100, 100-140 and 140-180 cm depths to determine NO3--N content. The twenty-year grain yield decreased in the order of MNPK≥MNP＞NPK＞MN＞NP＞M＞N＞CK. Corn yield of CK in 2000 was only 28.2% of that in 1984, and wheat in 2001 was 25.7% of that in 1982. Average impact of fertilizers on grain yield decreased in the order of N＞M＞P＞K. Yield response to N and P fertilizers increased with progression of the experiment. K fertilizer showed no effects on increase of grain yield during the initial 6 years (1982-1987), moderate effects in the next 5 years (1988-1992), and dramatic effects in the last 9 years (1993-2001). The straw yield trend was similar to grain yield. Accumulation and distribution of NO3--N in soil was significantly affected by annual fertilizations. Chemical fertilizers (NP and NPK) caused NO3--N accumulation in most subsoil layers, with major impact in the 20-140 cm depth. The combination of chemical fertilizers and M (MNP and MNPK) reduced soil NO3--N accumulation as compared to chemical fertilizers alone. In conclusion, long-term fertilization significantly improved grain and straw yield in this rotation. The findings suggest that it is important to balance the application of chemical fertilizers and manure in order to protect soil and underground water from potential NO3--N pollution while keeping high productivity in the Oasis agro-ecosystem.