Toward yield improvement of early-season rice: Other options under double rice-cropping system in central China

Rice (Oryza sativa L.) grain yields vary considerably between seasons under subtropical irrigated conditions. Reports on comparisons of grain yield between early- and late-season rice in subtropical environments are lacking. In order to evaluate the role of climatic and physiological factors under double rice-cropping system in determining rice grain yield in farmers’ fields, six field experiments were conducted in both early and late seasons from 2008 to 2010 in Wuxue County, Hubei province, China. For early season crop, the attainable yield was highest under dense planting (38.5 hills m−2) when N was applied at a rate of 120–180 kg ha−1. However, the effect of hill density on grain yield was relatively smaller for late season crop, while moderate hill density (28.1 hills m−2) and nitrogen rate (120 kg ha−1) were advantageous in terms of grain yield and lodging resistance. Remarkably higher grain yields were achieved in late season crops compared with early season crops, as the former had superiority over the latter in sink size (sink capacity, such as spikelets per m2) and biomass production. The comparatively lower yield under early season mainly resulted from slower growth during the vegetative phase, which can be attributed to the lower temperature rather than reduced mean daily radiation. Summary statistics suggested that there was ample opportunity to improve rice yield in early season crops, compared with late season crops. Correlation analysis further showed that spikelets per m2, panicles per m2, leaf area index at panicle initiation and flowering, biomass at physiological maturity and biomass accumulation after flowering should be emphasized for increasing grain yield, especially in early season crops under the double rice-cropping system in central China. Current breeding programs need to target strong tillering ability, large panicle size and greater grain filling (%) for early season crops, and high yield potential and lodging-resistance for late season crops as primary objectives.

► Rice grain yield was higher in the late season than the early season in central China.
► The late-season rice had advantages over early-season rice in sink size (sink capacity, such as spikelets per m2) and biomass production.
► Grain yield was positively correlated with biomass accumulation after flowering.
► Grain yield improvement in the early season seems more promising than the late season.
► The main agronomic and physiological traits responsible for high yield of the early-season rice were its strong tillering ability, large panicle size, high grain-filling percentage and greater biomass production.