| Irrigation area in Western Guanzhong Plain is the major wheat-growing area. In this area, great amount of fertilizers is always used to enhance the wheat yield. But in recent years, the fertilizers use were excessive and unbalanced. But, the crops yield wasn't increased significantly, and also the fertilizer use efficiency, economic benefits were decreased, and Environment was threated. According to the evaluation of the soil fertility in Zhouzhi, Hu, Fufeng County and Yangling region, many"3414"field experiments were carried out in this area to study the effects of nitrogen, phosphorus and potassium fertilizer application on wheat yield, N P Knutrients uptakes, and mineral N accumulation in the soil profile. In a word, the paper was wrote to provide some theories and technologies about scientific fertilization in this area. The results as following:(1) Soil fertility in the research area were measured, evaluated by the soil fertility evaluation standard of Shaanxi in the paper. The results showed that, soil organic matter was the forth fertility level (nine levels totally), soil total nitrogen was the sixth level (seven levels totally), soil available phosphorus was the forth level (eight levels totally), and soil available potassium was the second level (nine levels totally). The soil fertility was overall low. The rang of soil available P was large, and the soil available K was high. But, the mineral N accumulation was great in 2m soil profile before wheat seeding, the average in 1m soil profile was 262-381 kg/hm2, and 419-580 kg/hm2 in 2m soil profile. Maybe large N fertilizer use is the main reason.(2) The results of"3414"experiments in Zhouzhi County showed that the addition of the fertilizers increased the yield of winter wheat in comparison with the un-fertilized treatment. The response of the yield to N fertilizer was significantly higher than that of P and K fertilizer; and the responses of the yield to P and K fertilizer were similar. The economic optimum application rates of nitrogen, phosphorus and potassium fertilizers in the south plateau region of Zhouzhi were N 106 kg / hm2, P2O551 kg /hm2 and K2O 95 / hm2, respectively; for the central irrigation area, the corresponding rates were N 191 kg / hm2, P2O597 kg /hm2 and K2O 133 / hm2, respectively; and for the region with rich groundwater, N 194 kg / hm2, P2O580 kg /hm2 and K2O 127 / hm2, respectively.(3) Seventeen field experiments were used to assess the effects of the N2P2K0 N2P0K2 N0P2K2 N2P2K2 fertilization treatments on the N, P and K uptakes and fertilizers recovery. The results showed that the N, P, K uptakes, fertilizers use efficiency(UE) and partial factor productivity(PFP) were the highest in the N2P2K2 treatment which increased N,P uptakes significantly.(4) The two"3414"field experiments were carried out in Houzhai village and Wangcaitun village, which were used to study the effects of fourteen different N P K application treatments on nutrients accumulation. The results showed that all fertilizers applied treatments enhanced the N P K nutrients accumulation significantly, compared with the control treatment. The two significant ternary quadratic models were fitted to explain the effects of N P K fertilizer applications on nitrogen nutrients accumulation in winter wheat in Houzhai village and Wangcaitun village. The models showed that nitrogen nutrient accumulation was first increased and then decreased as nitrogen, phosphorus and potassium fertilization increased. Within the fertilization levels which were designed in the experiments, nitrogen nutrient accumulation was first increased and then decreased as nitrogen and potassium fertilization increased, and was increased as phosphorus application increased in Houzhai village; nitrogen nutrient accumulation was increased as nitrogen and phosphorus fertilization increased, and was decreased as potassium application increased. A significant linear model can be used to explain the effect of P fertilizer application on phosphorous accumulation in Houzhai village. So this model showed that phosphorus nutrient accumulation was increased as the phosphorus fertilizer application increased.(5) According to the results of the seventeen field experiments, the relationship between wheat yield and N P K nutrients accumulation can be explained by power function. The function showed that nutrients accumulation was increased slower and slower as the yield increased. Under the different wheat yield levels (4000～8000 kg/hm2) , the demands of N, P, K nutrients per 100 kg wheat grain were 2.52～3.06 kg N, 0.56～0.66 kg P, and 2.20～2.65 kg K, respectively. And they were decreased as the yield increased.(6) The eight experiments were designed to study the effect of nitrogen application on soil mineral nitrogen accumulation and distribution in 2m soil profile. The result showed that soil mineral nitrogen accumulation and distribution were also increased faster and faster, as the nitrogen application increased. When the nitrogen application was more than 200 kg/hm2, the soil mineral nitrogen accumulation and distribution were increased sharply.
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