An analysis of long-term rice yields in a wetland soil

Abstract

Since IR8 was released in 1966 the yield of this and other varieties have declined in long-term experiments on the IRRI farm. The negative yield trend of IR8 in one set of experiments conducted each year since 1966 was about 0.15 t ha −1 year −1 in the wet and twice this amount in the dry season. The yields of the highest yielding entries (HYE) in these experiments have declined by about 0.1 t ha −1 year −1 in both wet and dry seasons. Additional losses attributed to severe disease infestations were larger for IR8 (about 1.5 t ha −1) than for the HYE (1.0 t ha −1) in the wet season. In the dry season major disease outbreaks reduced IR8 yields by up to 1.6 t ha −1, but not the yields of HYE. The frequency of major disease occurrences, however, was higher for IR8 than for the HYE. The systematic decline of rice yields in these long term trials are implied to be mainly a consequence of a buildup of soil related problems — specially zinc deficiency and boron toxicity — a result of irrigating with alkaline, high boron water.