Interspecific interactions affect N and P uptake rather than N:P ratios of plant species: evidence from intercropping

Quantifying stoichiometry of crop N and P acquisition (i.e. removal from farmland) under different agronomic practices is essential for understanding nutrient budgets and optimizing N and P fertilizer application in agroecosystems. It is not clear how plant N and P uptake and N:P stoichiometry vary between monoculture and intercropping throughout an entire growing season under different N fertilization and mulching practices. Here, we addressed how plant interspecific competition for nutrients have affected the temporal dynamics of crop N and P uptake (and N:P ratios) in five cropping systems (wheat, maize and barley monocultures, and wheat/maize and barley/maize intercropping), under two N levels (0 and 225 kg N ha−1) and two maize mulching treatments (with and without). Wheat and barley had greater N and P competitive ability than maize, leading to an increase in N and P uptake of wheat and barley and a decrease in N and P uptake of maize during co-growth stages in intercropping. N:P ratios of three crop species decreased with plant growth. Crop-level N:P ratios were either not affected by intercropping or did not change consistently with N fertilization while film mulching decreased maize N:P ratios. Community-level N:P ratios of the two intercrops were different from those of the corresponding monoculture at maturity. Because (i) the proportion of N and P removal from intercropping differs from monocultures, and (ii) N and P uptake by crops is decoupled under N fertilization and mulching, these findings may have practical implications for the nutrient budget of intercropping systems.