Soil Nitrogen Loss in Runoff and Sediment as Affected by Level Trench and Crop Rotation

Compared with conventional tillage, level trench might reduce 7% in average of runoff amount on different slope land, the ammonium concentration in runoff increases 19%, its loss amount reaches 13.01 kg/(km²·a), also increases by 1.11 kg/(km²·a), the nitrate concentration in runoff reduced 27%, its loss amount is 16.18 kg/(km²·a) with reduction of 7.68 kg/(km²·a), in conclusion, the soil available nitrogen loss in level trench might reduce 6.57 kg/(km²·a) than that of conventional tillage. Level trench might retain 25% of soil loss, increase 13% of total nitrogen enrichment in sediment than that of conventional tillage, accordingly, soil nitrogen loss amount reaches 457 kg/(km²·a), it also reduces 13% of nitrogen loss than that of conventional tillage. Five years' rotation experiments show the erosion modules of rotation systems with a season black soybean, a season soybean, and two seasons black soybean, a black soybean, reach 896 and 984 t/(km²·a) respectively, their modules are twice less than that of rotation system with broom millet and potato.