Abstract: A 2-year field experiment was conducted to study the dynamics of soil nitrogen content and urease, proteinase, and nitrate reductase activities in a wheat/maize/soybean relay strip intercropping system under effects of five planting modes, i.e., wheat-soybean (A₁), wheat-sweet potato (A₂), maize (A₃), wheat/maize/soybean (A₄), and wheat/maize/sweet potato (A₅). Among the five planting modes, A₄ increased the soil total nitrogen content and urease and protease activities at flowering (or spinning) and maturing stages, and the total nitrogen content and urease and protease activities were relay strip intercropping > single cropping, soybean > sweet potato, and fringe row > central row. A₄ decreased the NO₃^--N and NH₄⁺-Ncontents of wheat and maize soil, and the nitrate reductase activity of wheat soil. The nitrate reductase activity of maize soil was higher in single cropping than in relay strip intercropping at jointing stage but was in adverse at maize spinning and maturiting stages, and the nitrate reductase activity of soybean soil was higher than that of sweet potato soil. At the branching stage of soybean, the soil NO₃^--N and NH₄⁺-N contents and nitrate reductase activity were higher in single cropping than in relay strip intercropping; whereas at flowering and maturing stages, the soil NO₃^--N and NH₄⁺-Ncontents and nitrate reductase activity were in the sequences of strip intercropping > single cropping, soybean > sweet potato, and center row > fringe row.

Key words: wheat/maize/soybean relay strip intercropping, soil nitrogen content, soil enzyme activity, nitrogen transformation