Effects Of Rotation With Legume And Nitrogen Application On Yield And Mineral Nutrition Of Wheat Grain And Its Soil Mechanism On Dryland Of The Loess Plateau

Wheat is the second important staple food after rice in China, and it is also the major staple food in northern China, especially in the provinces of Shaanxi, Gansu, Ningxia, Qinghai, and Xinjiang where soil micro-nutrient deficiency is common and the wheat flour is the most important source of food. Thus it is of profound importance to study effects of rotation with leguminous green manure and N input levels on wheat yield and grains nutrient contents on dryland of Loess Plateau which is a typical zone with nutritional deficient soil. A field experiment was carried out to study effects of rotation with legumes on wheat yield and grain nutrient contents with four rotation types (fallow-wheat, mung bean-wheat, soybean-wheat, and Qiu bean (local bean)-wheat) at four N input levels of 0, 108, 135 and 162 kg/hm2 on dryland of Loess Plateau. Meanwhile, we compared the content of mineral nutrients in 0~40cm soil during different growth stage of legumes and wheat. We investigated the soil mechanism on effects of rotation with leguminous green manure and nitrogen application on mineral nutrients of wheat grains. Obtained results showed that:1. Wheat yield was significantly decreased by 9.7%~26.6% due to water deficiency after rotation with legumes in the first year. However, effect of planting leguminous green manure on soil moisture was not significant in the second year. By rotation with legumes, the average contents of Zn, P, K, Ca, and Mg of wheat grains were increased by 22.0%, 18.5%, 8.8%, 7.9% and 7.8%, respectively. Among three N input levels, wheat yields were higher at 108 kg N/ha. With the increasing of N input, contents of N, S, Ca, Fe, Cu of wheat grains tended to be increased, P, Mg and Mn contents on the contrary were decreased, and K, Zn, B, Al were not significantly influenced.2. By comparison with control,after planting legumes in two consecutive years, soil organic matter was increased by 15.6% in the first year and 9.1% in the second year, and soil pH was decreased by 0.16 in the second year. Mineral nutrients content of 0~40cm soil layer was greatly improved after rotation with legumes. Evaluated by averaged content of nutrients in 0~40 cm soil before sowing of wheat in two respective year, nitrate nitrogen content was significantly increased by 93.4% and 96.1%; available phosphorus was increased by 8.1% and 32.0%; available potassium was increased by 11.6% and 13.9%; available manganese, copper, and zinc in 0~40cm soil layer was increased by 10.7%, 26.1%, 96.9% and 22.0%, 9.0%, 44.1%, respectively. Exchangeable calcium and magnesium of 0~40cm soil layer was significantly increased by 48.2% and 13.1% in the second year. At heading stage, soil available phosphorus, potassium and manganese contents were increased by 64.3%, 17.3% and 15.4%. Meanwhile, contents of soil nitrate nitrogen and available copper trended to be increased. At the harvest, contents of soil available phosphorus, potassium, manganese and zinc were still higher than that of the control. However, the content of soil ammonium nitrogen and available iron was not affected by planting leguminous green manure.3.Nitrogen input showed significant effects on soil mineral nutrition in early growth stage of wheat. With increasing of nitrogen input, soil nitrate nitrogen was increased by 17.6%~31.3% in 0~20cm soil layer at heading stage. Soil ammonium nitrogen was the highest when applied 108 kg N/hm2, but excessive nitrogen fertilizer input reduced the soil ammonium nitrogen content. However, high nitrogen input as 135 and 162 kg N/hm2 led to lower content of available phosphorus in 0~20cm soil layer but higher in 20~40cm soil layer compared to the control. Evaluated by averaged values in 0~40cm soil layers, contents of soil exchangeable magnesium were increased by 5.2% and 4.7% when applied 135 and 162 kg N/hm2. With nitrogen input increasing, soil available potassium content decreased by 4.3% to 6.8% in 0~20cm soil layer while soil exchangeable calcium content increased by 4.2% to 6.2% in 20~40cm soil layer. Short term nitrogen application had no significant effects on most of the soil trace elements, except soil available manganese which decreased significantly by 17.0%~19.0% in 0~20cm soil layer at heading stage as nitrogen input were increased. Soil mineral nutrients had no significant difference over different treatments at harvest of wheat.