Trends in irrigated-rice yields under intensive cropping at Philippine research stations

Abstract

Trends in rice yields were estimated from N-response experiments conducted at four locations in the Philippines – Maligaya Rice Research and Training Center (MRRTC), Bicol Rice and Corn Experiment Station (BRCES), Visayas Rice Experiment Station (VRES), and IRRI. The largest dry-season decline in yield of IR8 occurred at IRRI, where yields fell by about 0.3 t ha−1 year−1. IR8 yields in the same season fell by slightly more than 0.1 t ha−1 year−1 at BRCES, and did not decline at MRRTC. In the wet season, the yield decline of IR8 was highest at BRCES (more than 0.2 t ha−1); at IRRI it was more than 0.1 t ha−1 year−1. However, wet-season yields of IR8 or of the highest yielding entry (HYE) at MRRTC or VRES did not decline. Yield declines of the HYEs were less than those of IR8. In the dry season, they were more than 0.1 t ha−1 year−1 at IRRI but no significant decline was observed at MRRTC or BRCES. In the wet season, they were in the order of 0.1 t ha−1 year−1 at IRRI and BRCES. No significant wet-season yield decline was observed at MRRTC or VRES. Declining yields at IRRI are thought to be largely due to boron toxicity, zinc deficiency, increased disease and insect pressure and lodging. However, their causes at the other sites are not understood. IRRI has initiated experiments to examine this issue.