Yield of aerobic rice in rainfed lowlands of the Philippines as affected by nitrogen management and row spacing

Management practices need to be developed for aerobic rice, a system in which rice is grown under nonflooded conditions in nonsaturated soil. We evaluated the effects of amount and timing of fertilizer nitrogen (N) application and of row spacing on the yield of aerobic rice under rainfed conditions in the 2004 and 2005 wet seasons in 3 and 2 locations, respectively, in Central Luzon, Philippines. N timing and management were also evaluated under irrigated conditions at one location in the dry season in 2005. Yields were 3.1–4.9 t ha−1 with 60–150 kg ha−1 of applied N. Yields increased with N rate, up to rates of 60–150 kg ha−1 depending on site and season, but at rates beyond 90 kg ha−1 the risk of lodging increased, especially in the wet season. Yields were similar for different splits of N over time, and the regional practice for lowland rice of three to four splits can also be used for aerobic rice. Yields were similar for row spacings ranging from 25 to 35 cm. Although the number of panicles per square meter was significantly higher at 25-cm spacing than at 35-cm spacing, this difference was compensated for by significantly more spikelets per panicle at 35-cm spacing, while spikelet fertility and grain weight were similar for all row spacings. Lodging and bending resistance of stems were not affected by row spacing. The results suggest that a row spacing of 35 cm can be used to enable easier weeding between the rows, and allows for mechanized field operations in which tire tracks do not damage the crops.