Uptake and conversion efficiencies of NPK and corresponding contribution toyield advantage in cotton-based intercropping systems

Cotton-based intercropping is a popular agronomic practice in Northwest China. This agronomic practice addresses theconflict in planting area/space between cereals and cotton. However, not sufficient knowledge exists on the yield advantage and nutrientuptake and conversion of cotton-based intercropping. In this paper, the uptake and conversion efficiency of nitrogen (N), phosphorus(P) and potassium (K) were assessed in several cotton-based intercropping systems, including cotton/peanut, cotton/soybean,cotton/chickpea, cotton/onion, cotton/radish and cotton/line-chilli intercropping systems, and the corresponding monocropping systems.Then yield advantage and nutrient uptake and conversion of cropping systems were determined. Compared with weighted meanof monocultured crops of sole cropping systems, cotton/peanut, cotton/chickpea, cotton/onion and cotton/radish intercropping systemsincreased N uptake by the range of 18%~74%. Also, compared with corresponding weighted mean of monocultured crops, cotton/soybean and cotton/chilli intercropping systems decreased N uptake by 10% and 34%, respectively. P uptake under intercroppingsystems of cotton/peanut, cotton/chickpea, cotton/onion, cotton/radish and cotton/soybean was higher than that under the correspondingsole cropping systems by 5%~104%. However, the reverse was the case for cotton/chill, where it was lower by 6%. About20%~58% increase in K uptake was noted under cotton/peanut, cotton/onion and cotton/radish intercropping systems over the correspondingsole cropping systems. However, K uptake dropped by 19%~22% under cotton/soybean, cotton/chickpea and cotton/chilliintercropping systems over the corresponding sole cropping systems. Land equivalent ratios (LER) of cotton/chickpea, cotton/peanut,cotton/onion and cotton/radish intercropping systems were 1.02, 1.30, 1.12 and 1.68, respectively, indicating a significant yield advantage.However, LER of both cotton/soybean and cotton/chilli intercropping systems were 0.91 and 0.99, respectively, indicatingno yield advantage. The contributions of the uptake efficiencies of N, P and K to LER were 0.41~0.82, 0.25~1.04 and 0.15~0.59 incotton/peanut, cotton/onion and cotton/radish intercropping systems, respectively. The corresponding conversion efficiencies were?0.35~?0.04, 0.03~0.14 and ?0.16~0.01, respectively. Yield advantage of intercropping was mainly from enhanced nutrient uptakeefficiency, and not from nutrient conversion efficiency.