Nitrogen and phosphorus uptake and yield of wheat and maize intercropped with poplar

This study investigated the N and P uptake and yield performances of winter wheat (Triticum aestivum) and maize (Zea mays) upon intercropping with 1- to 2-year-old poplar (Populus x euramericana cl. "74/76'') trees compared to a sole wheat and maize rotation in fertilized and unfertilized subplots. Aboveground biomass, grain yield, yield components, and N and P contents of wheat and maize were measured in each plot, in addition to soil available N and P. No significant differences in biomass, grain yield, and N and P uptake of wheat were found between the intercropping and sole-crop systems within the same fertilization treatment. Maize biomass and grain yield decreased by 37% and 31%, and 28% and 34% for the fertilized and unfertilized treatment at maize maturity in the same order. The N and P contents in maize intercropped with poplar were found to be significantly lower than in the sole-maize. For the fertilized treatment, intercropping with poplar led to significantly lower soil NO3-N and Olsen-P in the 0-20-cm layer during the active wheat growth period and a significant increase in soil NO3-N and Olsen-P during the active maize growth period due to less N and P uptake by maize. The poplar induced a decrease in soil NO3-N and Olsen-P during both wheat and maize season under unfertilized conditions, thereby influencing the yield and nutrient uptake of intercrops. Therefore, enough available nutrients had to be provided for the agroforestry systems, especially during the active growth period of intercrops.