[Effects of straw returning amount and type on soil nitrogen and its composition]. / 秸秆还田量和类型对土壤氮及氮组分构成的影响.

Straw returning to soil can supplement soil nutrients required for crop growth, fertilize soil, and improve soil quality. To explore the long-term effect of straw returning on soil total nitrogen and its composition, herein, five treatments including no rice straw + no wheat straw returning (NRW), no rice straw + all wheat straw returning (W), all rice straw + no wheat straw returning (R), half rice straw + half wheat straw returning (HRW), and all rice straw + all wheat straw returning (ARW) were conducted in triplicate in Taihu Lake region, China. The effects of both straw amount and type were examined. Compared with the results obtained in 2007, the results herein obtained in 2017 showed that after 10 years of straw returning, soil total nitrogen and heavy fraction nitrogen increased, while light fraction organic matter decreased. Among the five treatments, ARW had the largest decrease in light fraction nitrogen of 8.09 g·kg-1; the R treatment had the highest contents of both total and heavy fraction nitrogen, and also the highest contents of ammonium and nitrate. There was no significant difference in alkali-hydrolyzable nitrogen among the five treatments. These results indicated that crop straw was the critical material source for soil nitrogen, and that the effects of straw returning on soil nitrogen depended on the type and amount of crop straw returned to soil. The changes of light fraction nitrogen were more sensitive to straw returning, while the heavy fraction nitrogen was relatively stable, which was the key fraction sustaining soil fertility. With the prolonging of straw returning, the relationship between the total nitrogen and diffe-rent nitrogen components changed. The processing manner of all rice straw returning + no wheat straw returning was the way that could most significantly enhance soil nitrogen content.

[Effects of poplar-amaranth intercropping system on the soil nitrogen loss under different nitrogen applying levels].

Characteristics of soil nitrogen loss were investigated based on field experiments in two types of poplar-amaranth intercropping systems (spacing: L1 2 m x 5 m, L2 2 m x 15 m) with four N application rates, i. e., 0 (N1), 91 (N2), 137 (N3) and 183 (N4) kg · hm(-2). The regulation effects on the soil surface runoff, leaching loss and soil erosion were different among the different types of intercropping systems: L1 > L2 > L3 (amaranth monocropping). Compared with the amaranth monocropping, the soil surface runoff rates of L1 and L2 decreased by 65.1% and 55.9%, the soil leaching rates of L1 and L2 with a distance of 0.5 m from the poplar tree row de- creased by 30.0% and 28.9%, the rates with a distance of 1. 5 m decreased by 25. 6% and 21.9%, and the soil erosion rates decreased by 65.0% and 55.1%, respectively. The control effects of two intercropping systems on TN, NO(3-)-N and NH(4+)-N in soil runoff and leaching loss were in the order of L1 > L2 > L3. Compared with the amaranth monocropping, TN, NO(3-)-N and NH(4+)-N loss rates in soil runoff of L1 decreased by 62.9%, 45.1% and 69.2%, while the loss rates of L2 decreased by 23.4%, 6.9% and 46.2% under N1 (91 kg · hm(-2)), respectively. High- er tree-planting density and closer positions to the polar tree row were more effective on controlling the loss rates of NO(3-)-N and NH(4+)-N caused by soil leaching. The loss proportion of NO(3-)-N in soil runoff decreased with the increasing nitrogen rate under the same tree-planting density, while that of NH(4+)-N increased. Leaching loss of NO(3-)-N had a similar trend with that of NH(4+)-N, i. e. , N3 > N2 > N1 > N0.