Alleviating soil sickness caused by aerobic monocropping: Responses of aerobic rice to nutrient supply

Yield decline is a major constraint in the adoption of monocropping of aerobic rice. The causes of the yield decline in the continuous aerobic rice system are still unknown. The objective of this study was to determine if nutrient application can mitigate the yield decline caused by continuous cropping of aerobic rice. Micro-plot experiment was conducted in 2005 dry season (DS) in a field where aerobic rice has been grown continuously for eight seasons from 2001 DS at the International Rice Research Institute (IRRI) farm. Pot experiments were done with the soil from the same field where the micro-plot experiment was conducted and aerobic rice has been grown continuously for 10 seasons. Apo, an upland rice variety, was grown under aerobic conditions with different nutrient inputs in field and pot experiments. The field micro-plot experiment showed that micronutrients had insignificant effect on plant growth under continuous aerobic rice cultivation but the combination of N, P, and K mitigated the yield decline of continuous aerobic rice. A series of pot experiments studying the individual effects of nutrients indicated that N application improved plant growth under continuous aerobic rice cropping, while P, K, and micronutrients had no effect. Increasing the rate of N application from 0.23 to 0.90 g per pot in the continuous aerobic rice soil increased the vegetative growth parameters, chlorophyll meter readings, and aboveground N uptake consistently. Our results suggested that N deficiency due to poor soil N availability or reduced plant N uptake might cause the yield decline of continuous cropping of aerobic rice.