小麦蚕豆间作体系氮素吸收累积动态及其种间氮素竞争关系

  【目的】  通过研究小麦//蚕豆间作地上部的氮含量和吸收量，明确不同氮水平下小麦//蚕豆间作的氮吸收累积特征，解析间作小麦和蚕豆种间氮素竞争关系。  【方法】  田间试验采用两因素随机区组试验设计，设置3个种植模式 (单作小麦，单作蚕豆及小麦//蚕豆间作) 及4个氮水平 (N0，N1，N2，N3)，其中小麦的4个施氮量依次为0、90、180、270 kg/hm2，蚕豆的4个施氮量依次为0、45、90、135 kg/hm2。测定了单间作小麦和蚕豆的产量、地上部氮累积含量，利用Logistic模型模拟小麦蚕豆的氮吸收关键参数及氮吸收动态，分析了间作小麦和蚕豆的氮素竞争关系。  【结果】  小麦//蚕豆间作整体平均提高小麦产量33.4% (除N3外)、降低蚕豆产量20.7%，N0和N1水平下，间作具有显著产量优势。通过Logistic模型分析发现，间作条件下小麦的氮吸收高峰比蚕豆晚12～19天。4个氮水平下，间作主要提高了小麦最大氮累积量 (A)、最大氮吸收速率 (R_max) 和初始氮吸收速率 (r)，却降低了蚕豆的A、达到最大氮吸收速率所需的时间 (T_max) 和R_max。在营养生长阶段，小麦的氮素竞争力低于蚕豆，施氮可提高小麦的氮素吸收量。从施氮水平和种植模式共同作用角度分析，N0、N1和N2水平下，间作分别提高小麦的R_max 34.1%、44.6%和21.0%。因此，当小麦达到氮吸收高峰后，间作分别提高小麦氮吸收速率和氮素累积量15.1%～48.4%和9.2%～28.9%，却降低蚕豆氮吸收速率和氮素累积量7.3%～28.4%和7.9%～14.0%。此时，间作小麦氮素竞争力大于蚕豆，在N1水平下小麦的氮素竞争力最强。  【结论】  小麦//蚕豆间作提高了小麦的初始及最大氮素吸收速率 (r和R_max)，提高了小麦生殖生长阶段的氮素吸收和累积，是间作小麦产量优势的基础。优化氮肥投入量，可调控小麦和蚕豆的种间竞争及互补关系，是小麦//蚕豆间作体系产量优势形成、氮素高效吸收利用的关键。

Dynamics of N acquisition and accumulation and its interspecific N competition in a wheat-faba bean intercropping system

  【Objectives】  We studied the nitrogen (N) content and N uptake of intercropping wheat and faba bean to clarify the relationship in nitrogen competition and accumulation between wheat and faba bean under different N application levels, so to propose a scientific nitrogen management for the intercropping system.  【Methods】  A field experiment of two factors with randomized block design was conducted under wheat monocropped, faba bean monocropped and wheat and faba bean intercropping conditions, and the four N levels were 0, 90, 180 and 270 kg/hm2 for wheat and 0, 45, 90, 135 kg/hm2 for faba bean. Both grain yield and above-ground N accumulation of wheat and faba bean were measured, and Logistic model was used to simulate the key N uptake parameters and N uptake dynamics. The N competition capacity between intercropping wheat and fababean was analyzed.  【Results】  The yield of wheat was increased by 33.4%, but faba bean yield was decreased by 20.7% in the intercropping system, as compared to corresponding mono-cropping. However, the intercropped wheat and faba bean had a yield advantage under N0 and N1 levels (LER > 1). Through Logistic model analysis, the peak N uptake of wheat was 12–19 days later than that of faba bean. Intercropping increased the maximum N accumulation (A), the maximum N uptake rate (R_max) and the initial N uptake rate (r) of wheat, but decreased the A, the time needed to reach the maximum N uptake rate (T_max) and R_max of faba bean under the four N levels. During the vegetative growth stage, intercropping tended to decrease N uptake and accumulation of wheat, and the N competitiveness of wheat was lower than that of faba bean in intercropping, but N application could improve the N competitiveness of wheat. Intercropping increased R_max of wheat by 34.1%, 44.6%, 21.0% under N0, N1 and N2 levels due to the interaction between N level and planting pattern, respectively. Thus, when wheat reached its N uptake peak, intercropping increased the N uptake rate and N accumulation of wheat by 15.1%–48.4% and 9.2%–28.9%, but decreased those values of faba bean by 7.3%–28.4% and 7.9%–14.0%, respectively. During reproductive growth stage, the N competitiveness of wheat was greater than that of faba bean, and the strongest N competitiveness of wheat was under N1 level.  【Conclusions】  The yield advantage of intercropping is due to the increased initial and maximum N uptake rate of wheat (r and R_max), and the increased wheat N uptake rate and N accumulation in the reproductive stage. Reasonable N input could relieve the competition and increase the synergistic role for the N nutrition of wheat and faba bean, to achieve high yield and high nitrogen efficiency.