Expanding row ratio with lowered nitrogen fertilization improves system productivity of maize/pea strip intercropping

Intercropping is increasingly applied to confront food security issues in a sustainable manner. However, whether changing of row ratio and lowering N fertilization will affect interspecific interactions in maize (Zea mays L.)/pea (Pisum sativum L.) strip intercropping is unknown. Here we determined interspecific competition and yield response of pea and maize in a substitutive strip intercropping field experiment with irrigation in arid northwestern China from 2009–2011. Expanding the maize-to-pea row ratio from 2 : 4 to 3 : 4 intensified interspecific competition by 39, 96 and 154 % at 45, 60 and 75 d after maize sowing, and increased crop growth dynamics index of maize by 102, 89 and 16 % during 75–105, 105–135, and 135–165 d after maize sowing. Accordingly, grain yield of pea and maize with row ratio 3 : 4 was improved by 12 and 8 %, respectively, compared to row ratio 2 : 4. Meanwhile, the overyielding effect of pea and maize with row ratio 3 : 4 at 28 and 35 %, respectively, was significantly greater than row ratio 2 : 4. Lowering N fertilizer rate from 450 to 300 kg N ha⁻¹ intensified interspecific competition without affecting grain yield of pea and maize in the intercropping system. Grain yield of pea was positively correlated with interspecific competition, while that of maize was positively correlated with crop growth dynamics index of maize. Consequently, expanding row ratio with reduced N fertilizer rate could optimize interspecific interactions and improve system productivity of maize/pea strip intercropping.