Yield and nutrient uptake dissected through complementarity and selection effects in the maize/soybean intercropping

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Abstract
The yield and nutrient uptake advantages in an intercropping system are commonly supposed to be driven by the overall functional complementarity and temporal/space niche differentiation between the species. However, studies on the separation of the complementarity effect (CE) and selection effect (SE) on yield and nutrient uptake to understand the underlying mechanisms of intercropping mediated by N application rates are relatively few. Here, field experiments with four N application rates (maize: 0, 180, 240, and 300 kg N ha−1; soybean: 0, 40, 80, and 120 kg N ha−1) were conducted to study yield and nutrient uptake advantages in the maize/soybean intercropping system in 2017 and 2018. Intercropping significantly enhanced the maize yield and decreased the soybean yield, and yield advantage was observed across all N application rates. Also, the gross profit was significantly affected by N application rates and intercropping, and the maximum increase in intercropped compared to that of monoculture appeared at the N2 treatment in 2018. Moreover, nutrient uptake was significantly affected by intercropping and N application rates; the N uptake of the intercropping system (on average of two years) was highest at the N2 application rate, which increased by 13.8% compared to that of monoculture system. CE and SE of grain yield were positive over the two‐year study and were both the main contributions. Furthermore, SE in N and P (only observed in 2017) uptake increased with the increase in N application rate, and SE was the main contribution to P uptake. Application of the additive partitioning method to intercropping may help to analyze the drivers of yield and nutrient advantage of intercropping and promote careful management of fertilizer application to improve nutrient use efficiency.

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