Optimised sowing date enhances crop resilience towards size-asymmetric competition and reduces the yield difference between intercropped and sole maize

Intercropping is becoming an attractive and profitable agricultural practice, and a growing body of literature investigate on the plant-plant interaction between intercrops. However, little is known on how sowing date alters interspecific interaction causing a yield difference between the intercropped and sole crop. A two-year field experiment was undertaken to investigate the impacts of varying competitive interaction on plant growth and grain yield of a maize/watermelon intercropping system. Both intercropped and sole maize were sown 28 days, 33 days and 38 days after a consistent transplanting date for watermelon to generate varying intensities of asymmetric competition between species in the maize/watermelon intercropping system. Growth patterns were monitored over two years and described with logistic growth curves. Compared with conventional sowing date, changes in maize sowing date significantly enhanced the intercropped maize grain yield by 21%-42%, but barely affected the sole maize yield, consequently reducing the yield difference between intercropped and sole maize. An earlier sowing date empowered the intercropped maize to reach the maximum absolute growth rate 11 days earlier, producing greater aboveground biomass and larger growth rate over its growing period, and thereby enhanced the maize resilience towards size-asymmetric competition derived from the presence of watermelon. Changes in the maize sowing date did not alter the fruit yield of intercropped watermelon in the most cases, but overmuch improvement in the aggressivity and growth rate of the maize sown on 13 June in 2014 caused a 16% reduction in fruit yield. We concluded that the yield difference can be reduced by adjusting the sowing date to manipulate plant-plant interaction between intercrops, and an optimal sowing date not only enhances crop growth but also brings on no penalty on companion crop yield.