小麦/玉米/大豆和小麦/玉米/甘薯套作对土壤氮素含量及氮素转移的影响

为探讨小麦/玉米/大豆套作对氮素营养的种间促进机制, 采用叶片¹⁵N富积标记法研究了小麦/玉米/大豆(A1)和小麦/玉米/甘薯(A2) 2种套作系统中不同施氮水平下的土壤培肥效果和氮素转移规律。结果表明,施氮可以提高小麦、玉米的土壤总氮含量,以施纯氮150~300 kg hm^-2处理最高;大豆较甘薯更有利于保持土壤肥力,施氮0、150、300和450 kg hm^-2水平下种植大豆后的土壤总氮含量比种植大豆前(小麦收获后)高38.6%、20.2%、9.4%和16.7%,而种植甘薯则降低总氮含量3.1%、1.8%、14.0%和3.8%。A1系统中小麦和玉米季土壤中NO₃-N含量低于A2系统,且随施氮量的增加而增加;大豆季土壤中NO₃-N含量高于甘薯季。A1和A2系统均存在¹⁵N的双向转移,¹⁵N转移量随施氮量的增加而降低,且A1的¹⁵N净转移量和转移强度高于A2;A1系统中小麦、玉米和大豆的¹⁵N净转移量比A2系统的¹⁵N净转移量分别高3.3%~12.1%、27.0%~166.2%和26.2%~78.7%。玉米与小麦之间的¹⁵N净转移方向为从玉米向小麦,玉米与大豆之间的¹⁵N净转移方向为从大豆向玉米,玉米与甘薯之间的¹⁵N净转移方向为从玉米向甘薯。

Effect of Wheat/Maize/Soybean and Wheat/Maize/Sweet Potato Relay Strip Intercropping on Soil Nitrogen Content and Nitrogen Transfer

The aim of this study was to characterize nitrogen transfer in the relay strip intercropping system of wheat/maize/soybean, and to investigate the N promotion mechanism. A pot experiment was conducted to determine the soil N content and transfer in the relay strip intercropping of wheat/maize/soybean and wheat/maize/sweet potato using the direct ¹⁵N foliar feeding technique. The N application rates were 0, 150, 300, and 450 kg ha^-1. The results showed that N application increased the soil total N contents in wheat and maize seasons. The total N content of soil reduced when N applied in an excessive rate, and the highest values of soil total N content appeared at the N rate of 150–300 kg ha^-1. Moreover, the soil total N contents in wheat and maize seasons in the relay strip intercropping of wheat/maize/soybean were higher than those in the wheat/maize/sweet potato system. After soybean planted in the relay strip intercropping, the soil total N contents increased by 38.6%, 20.2%, 9.4%, and 16.7% at applied N rates of 0, 150, 300, and 450 kg ha^-1, respectively. Whereas after sweet potato planted, they were reduced by 3.1%, 1.8%, 14.0%, and 3.8%, respectively. Therefore, the soybean season was beneficial to maintaining soil fertility. The soil NO₃-N contents in wheat and maize seasons increased with the raising of N application rate, and the values in wheat/maize/soybean system were lower than those in wheat/maize/sweet potato system. The soil NO₃-N contents in soybean season were higher than those in sweet potato season. Bi-directional ¹⁵N transfer existed in both relay systems. The amount of transferred ¹⁵N reduced with the increasing of N application rate. The strength and amount of net transferred ¹⁵N in the wheat/maize/soybean system were higher than those in the wheat/maize/sweet potato system. The amounts of net transferred ¹⁵N in wheat, maize, and soybean in the wheat/maize/soybean system increased by 3.3–12.1%, 27.0–166.2%, and 26.2–78.7% compared to the corresponding crops in the wheat/maize/sweet potato system, respectively. Moreover, the directions of the ¹⁵N transfer were evident, which were from maize to wheat, from soybean to maize, and from maize to sweet potato.