Effect of planting patterns on crop yield, nutrients uptake and interspecific competition in maize-soybean relay strip intercropping system

To deal with the contradiction between population growth and land shortage, maize-soybean relay strip intercropping system has become increasingly popular and widely adopted in Southeast China. The conventional maize-soybean relay strip intercropping system used by farmers have not been good for high maize-soybean yields and nutrient uptake. To therefore explore the characteristics of competition for resources between crops and the mechanism of yield increase under maize-soybean relay strip intercropping system, a two-year field experiment was conducted where the effects of planting patterns on crop yield, nutrient uptake and interspecies competition for resources were investigated. The tested planting patterns included maize-soybean relay intercropping in continuous strips with wide-narrow rows (A1), maize-soybean relay intercropping in rotation strips with wide-narrow rows (A2), maize-soybean relay intercropping in continuous strips with equal rows (A3), maize monoculture (A4) and soybean monoculture (A5). The density of maize and soybean under relay intercropping was equal to that under monoculture. The results showed that compared with monoculture and equal width spacing, relay strip intercropping decreased maize grain yield while increased soybean bean yield significantly. Maize grain yield under A2 treatment was 4.9% and 5.7% lower than those under A4 and A3 treatments, respectively. However, soybean bean yield under A2 treatment was 25.5% and 89.2% higher than those under A5 and A3 treatments, respectively. Compared with A1 treatment, maize grain yield and N, P, K uptake increased under A2 treatment. The maize grain yield and N, P, K uptake under A2 treatment were 7.5%, 18.5%, 9.1% and 14.1% higher than those under A1 treatment. However, yield and N, P, K uptake of soybean were not significantly different between A2 and A1 treatments. Compared with the monoculture treatments, the economic coefficient and nutrient harvest index of soybean in maize-soybean relay strip intercropping systems significantly increased. The economic coefficient and N, P, K harvest indexes of soybean under A2 treatment increased by 40.9%, 11.9%, 20.6% and 39.9%, respectively. In maize-soybean relay strip intercropping systems, maize competition was weaker than that of soybean for N, P, K (A_ms<0,CR_ms<1). However, rotation helped improve interspecific competition and nutrient competition ratio of maize. In 2013, interspecific competition was close to 0 while nutrient competition ratio was close to 1 under A2 treatment. Comparison of A2 with A1 and A3 treatments showed that rotation benefited harmonious symbiosis between maize and soybean. This symbiosis enhanced nutrient uptake of both maize and soybean, subsequently increasing yield and land equivalent ratio (LER) of the cropping system.