Effect of planting density on grain yield and water productivity of rice (Oryza sativa L.) grown in flooded and non-flooded fields in Japan

The effect of planting density on grain yield and water productivity was evaluated in rice (Oryza sativa L.) grown in non-flooded lowland fields in Japan in comparison with flooded fields. One rice cultivar, IR24 was grown both in flooded and non-flooded lowland fields in 2001 and 2002, and only in flooded field in 2003, with different planting densities ranging from 5.6 to 44 hills m(-2). Another rice cultivar, Dontokoi was also grown in 2001. Straw mulching treatment was added in non-flooded field in 2002. In non-flooded fields, standing water disappeared from 36 and 8 days after transplanting until maturity in 2001 and 2002, respectively, the mean water content of surface soil during non-flooded period was 72 % g g(-1) on a dry basis and 63 % v v(-1). Grain yield in flooded fields (637 g m(-2); average of 2001 and 2002) was higher than that in non-flooded fields (467 g m(-2); average of 2001 and 2002), due to larger spikelet number per panicle in both years, larger 1000 grain weight in 2001, and higher percentage of ripened grains in 2002. Straw mulching tended to increase sink size but reduced percentage of ripened grains, resulting in no yield advantage in 2002. Water productivity in non-flooded fields (0.34 kg m(-3); average of 2001 and 2002) was significantly higher than that in flooded fields (0.14 kg m(-3)). Grain yield increased with higher planting density in flooded fields in 2001 and 2003. In non-flooded fields, however, the effects of planting density on grain yield were little or marginal in both cultivars, due to the trade-off relationship between panicle number and spikelet number per panicle. This study showed that higher planting density would result in higher grain yield in favourable flooded fields, but is not advantageous for higher grain yield under non-flooded lowland fields in Japan in improved cultivars with relatively high tillering and yielding abilities.