| Western Guangzhong region is one of major grain crop production region in Shaanxi Province. Summer maize and winter wheat rotation is the main rotation system in this region. In recent years, high amounts of chemical fertilizer were applied by the farmers in order to increase the crop yield. It increased the soil fertility greatly. The excessive application of fertilizers became a serious problem, especially for the usage of nitrogen fertilizer. This results in the great loss of N fertilizer, damages the environment, affects the human health.Therefore, more than 20 field experiments designed with"3414"plan and the experiments of long-term cultivation pattern under maize-wheat rotation system were carried out to studythe relationship between fertilization and accumulation of nitrogen in soil of the maize-wheat rotation; and the nutrient balance in the different cultivation patterns was also evaluated to analyse the nutrient management and fertilization in Guanzhong region in Shaanxi. The results were as following:(1) More than 20 field experiments designed with"3414"plan were carried out in Huxian County and Zhouzhi County, Guanzhong Plain, Shaanxi from 2008 to 2009 in order to evaluate the accumulation of NO3-N in soil profiles after harvesting winter wheat; and their relationship with the apparent N budget in soil was also studied. The results showed the amount of NO3-N accumulated in the soil profiles and its extent to leach into the deeper soil layer increased significantly as the nitrogen fertilizer usage increased. When the N fertilizer rate added reached to the N2 level (180～240 kg/ha), positive budget of nitrogen in soil was observed in some experiment sites; and when N fertilizer rate reached to the N3 level (270～360 kg/ha), positive budget of nitrogen in soil was observed in the all experiment sites. There was a positive correlation between the balances of soil N and the accumulation of NO3-N in 0-2 m of soil profiles. It indicates the amount of NO3-N in soil profile was mainly determined by the N budget balances in soil. The NO3-N accumulated in soil profile increased about 62.5 kg/ha when N balance in soil was at each 100 kg/ha.(2) The six field experiments designed with"3414"plan were carried out in Huxian County and Zhouzhi County to evaluate the accumulation of NO3-N in soil profiles after harvesting summer maize; and their relationship with the apparent N budget in soil was also studied. The results showed the amount of NO3-N accumulated in the soil profiles and its extent to leach into the deeper soil layer increased significantly as the nitrogen fertilizer usage increased. When the N fertilizer rate added reached to the N1 level (90～150 kg/ha), balance of nitrogen in soil was observed in some experiment sites; and when N fertilizer rate reached to the N3 level (270～450 kg/ha), positive budget of nitrogen in soil was observed in the all experiment sites. There was a positive correlation between the balances of soil N and the accumulation of NO3-N in 0-2 m of soil profiles. It indicates the amount of NO3-N in soil profile was mainly determined by the N budget balances in soil. The NO3-N accumulated in soil profile increased about 47.6 kg/ha when N balance in soil was at each 100 kg/ha.(3) A 7-year's field experiment was used to study the effects of long-term cultivation pattern and nitrogen application rate on N, P and K nutrient net balances soil under maize-wheat rotation system, and their relationship with nutrient contents in soil was also evaluated. The results showed that the nutrient deficits in soils under the two patterns with straw additions, i.e., mulching and furrow planting, were lower than that of conventional and water-controlling patterns, indicating that straw addition plays an important role in balancing the nutrients in soil. Nitrogen in soil added with 120 kg/ha of nitrogen fertilizer was near balance; when nitrogen fertilizer was increased to 240 kg/ha, nitrogen accumulation in soil increased significantly (averaged at 1471 kg/ha). There were significantly positive relationships between nitrogen balance value in soil and nitrate accumulated in 0–2 m soil profile, and P and K balance values in soil and Olsen-P and available K in soil. The accumulated nitrate increased about 38.3 kg/ha when N balance in soil was increased at each 100 kg/ha. The deficit of each 100 kg/ha of P and K nutrients in soil, Olsen-P and available K in soils declined about 3.5 mg/kg and 1.0 mg/kg, respectively. It indicates the deficit and accumulation of available nutrients in soils was mainly determined by the nutrient balances in soil. |
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