Characteristic of Nitrogen Acquisition and Proportion for Different Rows of Intercropping Wheat and Its Response to Nitrogen Rates

Two years of field experiments were conducted to investigate the wheat nitrogen(N) uptake, accumulation and N use efficiency in wheat and faba bean strip intercropping system. Four N levels(the N application rate for wheat at N₀, N₁, N₂, and N₃ levels was 0, 90, 180 and 270 kg/hm², respectively) and 2 planting patterns including mono-cropped wheat(MW) and wheat and faba bean strip intercropping(W//F) were designed, so as to further reveal the mechanism of high N use efficiency in W//F. The results showed that W//F only increased border row intercropping wheat(IW₁) shoot N content at jointing stage as compared to MW, and no difference in shoot N content between inner intercropping wheat and MW was found. However, the wheat spike N content was increased when wheat intercropped with faba bean under N₀, N₁ and N₂ levels, and the tendency was IW₁(border row wheat which close to the faba bean in a intercropping pattern) > IW₂(the second row of intercropping wheat which slightly far away from the faba bean in a intercropping pattern) > MW(mono-cropped wheat) = IW₃(the third row of intercropping wheat which far away from the faba bean in a intercropping pattern). Secondly, the more N was allocated to wheat spike when wheat intercropped with faba bean, intercropping significantly increased N uptake in wheat spike, especially at maturity, the N accumulation in IW₁ and IW₂ spikes was significantly higher than MW at 4 nitrogen levels(N₀, N₁, N₂, and N₃), with increases of 40.23%–21.84% and 31.78%–10.13%, respectively; the N allocation proportion of IW₁ and IW₂ spikes increased by 19.74%–9.87% and 37.09%–4.65%. Wheat N use efficiency in intercropping either row was higher than MW, and N use efficiency for IW₁, IW₂ and IW₃ increased by 17.26%, 18.20% and 19.52% in comparison with MW in 2 years experiments; the overall nitrogen harvest index showed IW₁ = IW₂ > IW₃ > MW. In conclusion, W//F seldom changed wheat N content in leaf, but increased wheat spike N content and improved N shift from stem and leaf to spike. Both border and inner row effect were help to increase wheat N uptake and utilization in intercropping system. Optimal N application rates to stimulate intercropping advantage of inner row could maximize intercropping saving N effect.