Uptake and utilization of nitrogen, phosphorus and potassium as related to yield advantage in wheat/soybean intercropping

Nitrogen, phosphorus and potassium absorption efficiency and utilization efficiency in the intercropping or sole cropping of wheat and soybean were investigated by field plot and microplot experiments. The results showed that nitrogen, phosphorus and potassium uptakes by intercropped species were higher than the weighted means of uptakes by sole cropping species; Increases in N, P and K uptake by intercropped species over sole cropping species were 24%～29%, 6%～27% and 24%～26%, respectively. However, nitrogen, phosphorus and potassium utilization efficiency (kg biomass per kg nutrient uptake) were reduced due to intercropping. The reductions in the N, P and K utilization efficiency of intercropping ranged from 5% to 20%, from 5% to 7% and from 6% to 32%, respectively. Land equivalent ratio(LER) analysis in term of N, P and K utilization efficiency showed that the increase in LER over unity was due largely to a higher total uptake of nutrients by the component crops in the intercropping than by the sole crops. The greater nutrient harvest index of intercropped soybean than that of sole soybean also contributed to the yield advantage. Interspecific root partition experiment demonstrated that interspecific root intermingle also affected nutrient utilization efficiency in intercropping.