Effects of ratios of ammonium /nitrate nitrogen on the competition and complementarity of wheat and faba bean intercropping systems^*

It is of great significance to investigate the competition relationships and compensation effect among crops in intercropping systems under different nitrate-to-ammonium nitrogen ratios, which is important for elucidating the mechanisms driving system stability and guiding rational fertilization practices. This study take wheat (Tricum aestivum) and faba beans (Vicia faba) intercropping system as subjects, different ratios of nitrate and ammonium nitrogen were used to measure crop yield and biomass under intercropping condition, namely nitrate: ammonium nitrogen =0:4(N1), nitrate: ammonium nitrogen =1:3(N2), nitrate: ammonium nitrogen =2:2(N3), nitrate: ammonium nitrogen =3:1(N4), nitrate: ammonium nitrogen =4:0(N5). The root shoot ratio, interspecific competitiveness (AWF), relative intensity of impact(RII), net effect(NE), compensation effect (CE)and selection effect (SE)of intercropping were calculated to determine the effects of different nitrate and ammonium nitrogen ratios on interspecific competition and complementarity. The results show that the land equivalent ratio of intercropping crop was greater than 1 under different treatment conditions. Compared with other treatments, the partial land equivalent ratio of faba bean had significant difference sand reached the maximum value under N2 treatment. Among all ammonium nitrate nitrogen ratio treatments, the AWF of wheat was all greater than 0, and AWF of wheat was the most obvious under N2 treatment. Compared with other treatments, the relative action strength (RII) of wheat under N2 was significantly increased by 1.38-6.25 times(p≤0.05). The compensation effect CE of intercropping system is greater than 0, the selection effect SE is less than 0, and CE reaches the maximum value under N2 treatment. The interspecific competitiveness and relative interaction intensity of wheat were obvious stronger than faba bean in wheat and faba bean intercropping system. There was a positive correlation between interspecific competitiveness of wheat and compensation effect CE, and there was a positive correlation between partial soil equivalent ratio PLERf of faba bean and compensation effect CE in intercropping system, respectively. In conclusion, the ratio of ammonium and nitrate nitrogen affects the competitiveness and complementarity in wheat and faba bean intercropping system, and N2 treatment has the most obvious effect in intercropping system.