Wheat/maize or wheat/soybean strip intercropping I. Yield advantage and interspecific interactions on nutrients

This study investigated yield advantage of intercropping systems and compared N, P and K uptake by wheat, maize, and soybean in two field experiments in Gansu province. At Baiyun site the field experiment compared two P levels (0 and 53 kg P ha(-1)), two planting densities for wheat and maize, and three cropping treatments (wheat/maize intercropping, sole wheat and sole maize). The design for the wheat/soybean intercropping experiment at Jingtan site was similar, except that fertilization rates were 0 and 33 kg P ha(-1) without plant density treatment. Yield and nutrient acquisitions by intercropped wheat, maize and soybean were all significantly greater than for sole wheat, maize and soybean with the exception of K acquisition by maize. Intercropping advantages in yield (40-70% for wheat intercropped with maize and 28-30% for wheat intercropped with soybean) and in nutrient acquisition by wheat resulted from both the border- and inner-row effects. The relative contribution to increasing biomass was two-thirds from the border-row effect and one-third from the inner-row effect. Similar trends were noted for N, P and K accumulation. During the co-growth period, lasting for about 80 days from maize or soybean emergence to wheat harvesting, yield and nutrient acquisition by intercropped wheat increased significantly while those by maize or soybean intercropped with wheat decreased significantly. Aggressivities of wheat relative to either maize (0.26-1.63 of A(wm)) or soybean (0.35-0.95 of A(ws)) revealed the greater competitive ability of wheat than either maize or soybean. The nutrient competitive ratio, 1.09-7.54 for wheat relative to maize and 1.2-8.3 for wheat relative to soybean, showed that wheat had greater capability to acquire nutrients compared to soybean and maize. Comparison of overall N and K acquisition by intercropping with weighted means of those of sole cropping revealed interspecific facilitation in nutrient acquisition during co-growth. (C) 2001 Elsevier Science B.V. All rights reserved.