Wheat and faba bean intercropping to improve yield and response to nitrogen

The wheat and faba bean intercropping system improves crop yield. However, there are few systematic reports on the relationship between the yield advantage and the interspecific interaction and its response to nitrogen fertilizer. Nitrogen applications were tested to improve nitrogen management in intercropped legumes and grasses, gather information on efficient nutrient use, and determine the interspecific influence on wheat and faba bean yields. The field positioning test was conducted from 2015 to 2017 to study yield advantages and interspecies relationship of wheat||faba bean intercropping system under various nitrogen application levels:no nitrogen (N0), low nitrogen (N1, 90 kg·hm^-2), conventional nitrogen (N2, 180 kg·hm^-2), and high nitrogen (N3, 270 kg·hm^-2). Compared with monocropped wheat, the intercropped wheat yield was significantly higher in all treatments2016:24.55% (N0), 20.71% (N1), 19.92% (N2), 16.77% (N3); 2017:35.89% (N0), 28.63% (N1), 23.32% (N2), 18.25% (N3). The mono and intercropped faba bean yields were both around 4 000 kg·hm^-2. The land equivalent ratio of the intercropping system under different nitrogen levels was N0 > N1 > N2 > N3 > 1, and the average intercropping productivity reached 5 023 kg·hm^-2 in two years. The intercropped wheat dry matter accumulation ratio after flowering, transfer rate, and contribution rate increased by 37.68%, 7.95%, and 10.59%, respectively, and the intercropped faba beans increased by 19.66%, 41.43%, and 17.64%, respectively, compared with the monocultured crops. The increase rate decreased as nitrogen increased, and the intercropped wheat dry matter accumulation ratio after flowering was significantly different at N2 and N3 levels in 2016. The average wheat relative interaction indexes were 0.13 (N0), 0.11 (N1), 0.10 (N2), and 0.08 (N3), showing mutually beneficial effects, but the faba bean indices were -0.008 (N0), -0.03 (N1), -0.08 (N2), and -0.08 (N3), indicating a competitive effect. The average wheat relative competition intensity values were -0.19 (N0), -0.08 (N1), 0.21 (N2), and 0.32 (N3), indicating intraspecific competition at low nitrogen levels (N0, N1) and interspecific competition at conventional (N2) and high (N3) nitrogen levels. All faba bean values indicated intraspecific competition:-0.75 (N0), -0.75 (N1), -0.66 (N2), and -0.65 (N3). The relative interspecific competitiveness values of wheat versus faba beans were 0.51 (N0), 0.54 (N1), 0.56 (N2), and 0.58 (N3), suggesting different degrees of competitive advantage. Competitiveness was significantly correlated (a quadratic curve) with the above-ground dry matter of the intercropping system. The maximum mixed dry matter mass of the intercropping system (16 093 kg·hm^-2) was reached when the wheat versus faba bean interspecific competitiveness value was 0.629 2. Wheat and faba bean intercropping reduced the interspecific competition intensity in a low nitrogen environment (N0, N1). It also expanded the mutually beneficial effects and competitive advantages of wheat and increased the dry matter accumulation ratio after flowering and the dry matter contribution rate of intercropping crops. The maximum competitive advantage of intercropped wheat was at the conventional nitrogen level (N2, 180 kg·hm^-2).