Alleviating soil sickness caused by aerobic monocropping: Responses of aerobic rice to fallow, flooding and crop rotation

Yield decline is a major constraint in the adoption of continuous cropping of aerobic rice. Therefore, monocropping system of aerobic rice should be avoided and crop rotation should be encouraged. The objective of this study was to examine if fallow and rotation with flooded rice and upland crops can reverse the yield decline of continuous aerobic rice. A long-term field experiment was conducted from 2001 dry season (DS) at the International Rice Research Institute (IRRI) farm and a severe yield decline was observed when aerobic rice has been grown continuously. The yields of aerobic rice after two-season fallow and after three-season flooded rice were significantly higher than that of continuous aerobic rice. The effects of fallow and rotation with flooded rice on yield improvement were attributed to higher total biomass production, larger sink size (spikelet m(-2)), and greater 1000-grain weight. Increases in yield response to N application and soil water holding capacity and decrease in 0-10 cm soil bulk density of aerobic rice after fallow and rotation with flooded rice were observed. Aerobic rice yielded more after two seasons of upland crops than after two seasons of fallow. Our experiments suggest that crop rotation and fallow could be used to reverse the yield decline of continuous aerobic rice. Studies on the mechanisms of the effects of crop rotation and fallow on yield improvement of aerobic rice will help to find the causes of yield decline due to the monocropping of aerobic rice.