Mixed-cropping systems of different rice cultivars have grain yield and quality advantages over mono-cropping systems

Mixed-cropping system is a centuries-old cropping technique that is still widely practiced in the farmers field over the globe. Increased plant diversity enhances farmland biodiversity, which would improve grain yield and quality; however, the impacts of growing different rice cultivars simultaneously were rarely investigated. In present study, five popular rice cultivars were selected and ten mixture combinations were made according to the growth period, plant height, grain yield and quality, and pest and disease resistance. Seedlings of the five cultivars and ten mixture combinations (mixed-sowing of the seeds in an equal ratio, then mixed-transplanting and finally mixed-harvesting) were grown in plastic pots under greenhouse during the early and late growing seasons in 2016. Results showed that, compared with the corresponding mono-cropping systems, almost all combinations of the mixed-cropping systems have advantages in yield related traits and grain quality. Compared with the mono-cropping systems in the early and late growing seasons in 2016, mixed-cropping systems increased the number of spikelets per panicle, seed-setting rate, and grain weight per pot and harvest index by 19.52% and 5.77%, 8.53% and 4.41%, 8.31% and 4.61%, and 10.26% and 6.98%, respectively (paired t-test). In addition, mixed-cropping systems reduced chalky rice rate and chalkiness degree by 33.12% and 43.42% and by 30.11% and 48.13% in the early and late growing seasons, respectively (paired t-test). These results may be due to enhanced SPAD indexes and photosynthetic rates at physiology maturity in mixed-cropping systems. In general, it was found that mixed-cropping with different rice cultivars have potential for increasing grain yield and improving grain quality.