Double cropping of rice in China went through three phases: continuous cropping replacing intercropping, japonica varieties replacing indica varieties in the second cropping and use of hybrid varieties.
In 1984 the areas with double cropping of rice amounted to 10.4 million hectares, accounting for 31.3% of the total rice areas. The mean yield obtained by double cropping was 9.87 t/ha or 61.15 higher than that by single cropping. In recent years, the yield obtained by double cropping has increased due to the cultivation of hybrid rice varieties. The area in which hybrid rice varieties were used for the second cropping accounted for 58.1% of the total area in Hunan Province. The highest yield for double cropping of hybrid rice for 36.9 hectares amounted to 14.83 t/ha.
The major constraints encountered included low temperature injury of the first crop at the seeding stage, transplanting of the second crop at a late time and low temperature including spikelet sterility at the flowering time in the second crop.
The current research activities aim at the following objectives: variety improvement, increase of the benefit of and studies on the effect of the rice double cropping system on soil fertility.
The potential to develop double cropping of rice will be considerable in future in China.