Effect of row spacing under maize-soybean relay intercropping system on yield, competition, and economic returns

Interrow spacing of intercrop species directly affects yield and competition indices such as land equivalent ratio of intercropping. The objectives of this research were to analyze (i) the maize and soybean yields under different spatial arrangements in maize-soybean relay strip intercropping (MSR) and (ii) the interspecies competition to provide a basis for optimization of row-spacing in MSR. The field trial was conducted in 2011 and 2012 at the Research Farm of the Sichuan Agricultural University in Yaan to determine the impacts of various interrow planting distances on yield and competition indices in cereal (maize crop)-legume (soybean crop) relay strip intercropping. Three planting arrangements were utilized based on the distance between maize-maize, maize-soybean, and soybean-soybean as (T1) 50, 40, and 70 cm, (T2) 50, 50, and 50 cm, and (T3) 50, 60, and 30 cm, respectively, and comparison was made with the sole maize (SM) and sole soybean (SSB). Experimental results revealed that grain yield of maize crop was improved with enhancing row spaces between maize and soybean, while "low-high-low" trend was observed for soybean yield in T1, T2, and T3, respectively, in both years. Competitive ratio, aggressivity, and relative crowding coefficient were consistently greater for maize than soybean in all treatments. The highest LER (1.67) was reported in T2 treatment, which was 9% and 4% higher than in T1 and T3, respectively. Higher LER explains that both crops are facilitating each other in a positive way and increase the average net income of T2 as compared to T1 and T3. Enhancing distance between maize-soybean rows with reducing distance between soybean rows put pressure on soybean due to intraspecific competition. Combined results of competitive indices and economic analysis showed that intercrops performed at their maximum in treatment T2. Therefore, the maximum intercropping advantages can be achieved by changing the row spacing, which determines the competitive relationship and productivity of MSR.