The effects of soil drying and rewetting on rice growth in lowland aquatic Ferralsols in the southeastern forest region of Madagascar

In the southeastern-forest region of Madagascar, the year-around anaerobic condition of most lowlands favors soil organic matter (SOM) accumulation, while the inherently nutrient-poor soils limit rice yields. Accelerating decomposition of the accumulated SOM through the soil surface drainage before transplanting is a conceivable approach to improve rice production. However, the effect of soil drying on rice growth has been little studied in highly weathered Ferralsols. A pot experiment was conducted to examine the soil-drying effect on rice growth. One-month period of the soil drying before transplanting substantially increased the biomass production compared to those grown in the continuously submerged soils, which was mainly attributable to the large N uptakes derived from the 'soil-drying effect'. However, soil-drying treatment decreased the physiological nitrogen use efficiency (PNUE: gBiomass/gNuptake) associated with the reduced plant P and K concentrations. Application of NPK fertilizer ameliorated the PNUE, and plant P and K concentrations. However, the plant K and Si dilution with soil-drying treatment and plant Si dilution with NPK fertilizer application negatively affected grain fertility due to blast infection. Our study indicated balanced nutrient management would be important to maximize the benefit of the soil-drying effect, and to prevent biotic damages to rice plants.