Cotton-based intercropping is a popular agronomic practice in Northwest China that addresses the conflict on planting area between cereals and cotton. However, not sufficient knowledge exists on the yield advantage, nutrient uptake 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: cotton-peanut, cotton-soybean, cotton-chickpea, cotton-onion, cotton-radish, cotton-line-chilli intercropping systems and the corresponding monocropping systems. Yield advantage, nutrient uptake and conversion of cropping systems were determined.

Compared with weighted mean of monoculture crops of sole cropping systems, cotton-peanut, cotton-chickpea, cotton-onion and cotton-radish intercropping systems increased N uptake by the range of 18-74%. Compared with the corresponding weighted mean of monoculture crops, cotton-soybean and cotton-chilli intercropping systems decreased N uptake by 10% and 34%, respectively. P uptake under intercropping systems of cotton-peanut, cotton-chickpea, cotton-onion, cotton-radish and cotton-soybean was higher than that under the corresponding sole cropping systems by 5-104%. However, the reverse was the case for cotton-chill, where it was lower by 6%. About 20-58% increase in K uptake was recorded under cotton-peanut, cotton-onion and cotton-radish intercropping systems over the corresponding sole cropping systems. However, K uptake dropped by 19-22% under cotton-soybean, cotton-chickpea and cotton-chilli intercropping 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 ad-vantage. However, LER of both cotton-soybean and cotton-chilli intercropping systems were 0.91 and 0.99, respectively, indicating no 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 in cotton-peanut, cotton-onion and cotton-radish intercropping systems, respectively. The corresponding conversion efficiencies were 0.3-0.04, 0.03-0.14 and 0.16-0.01, respectively. Results indicate that yield advantage of intercropping occurred mainly from enhanced nutrient uptake efficiency, and not from nutrient conversion efficiency.