不同施氮水平下杨树-苋菜间作系统对土壤氮素流失的影响

采用田间试验方法,研究了杨树 苋菜间作系统,即株行距2 m×5 m(L₁)和2 m×15 m(L₂)在0(N₀)、91(N₁)、137(N₂)和183(N₃) kg·hm^-2施氮水平下的土壤氮素流失特征.结果表明: 不同施氮水平对地表径流量、淋溶量和土壤侵蚀量的控制效果均为L₁＞L₂＞L₃ (单作苋菜);L₁、L₂地表径流量分别比L₃降低65.1%、55.9%;L₁、L₂距林带0.5 m处淋溶量比L₃降低30.0%、28.9%,距林带1.5 m处淋溶量比L₃降低25.6%、21.9%;L₁、L₂土壤侵蚀量分别比L₃降低65.0%、55.1%.对地表径流和淋溶损失中TN、NO₃^--N、NH₄⁺-N流失量的控制效果均为L₁＞L₂＞L₃;常规施氮(91 kg·hm^-2)水平下,L₁地表径流中TN、NO₃^--N、NH₄⁺-N流失量较L₃分别降低62.9%、45.1%、69.2%,L₂较L₃分别降低23.4%、6.9%、46.2%;杨树间作密度越大、距离林带越近,对土壤NO₃^--N、NH₄⁺-N的淋溶损失削减作用越强.同一间作密度下,随着施氮量的增加,地表径流中NO₃^--N流失比例减少,NH₄⁺-N流失比例增加;淋溶流失中
NO₃^--N、NH₄⁺-N浓度变化趋势一致,均为 N₃＞N₂＞N₁＞N₀.

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×5 m, L₂ 2 m×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 decreased 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, NO₃^--N and NH₄⁺-N in soil runoff and leaching loss were in the order of L₁＞L₂＞L₃. Compared with the amaranth monocropping, TN, NO₃^--N and NH₄⁺-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. Higher tree planting density and closer positions to the polar tree row were more effective on controlling the loss rates of NO₃^--N and NH₄⁺-N caused by soil leaching. The loss proportion of NO₃^--N in soil runoff decreased with the increasing nitrogen rate under the same tree planting density, while that of NH₄⁺-N increased. Leaching loss of NO₃^--N had a similar trend with that of NH₄⁺-N, i.e., N₃＞N₂＞N₁＞N₀.