Less yield reduction induced by high temperature in a paddy field under organic fertilizer management in Tochigi prefecture

抄録

In 2010, rice growth and yield were compared between farmer's fields under different fertilization practices: application of rice straw and bran for 11 years (O-11), the same but for 2 years (O-2), and a combination of synthetic fertilizer and cow manure (F). With the daily maximum air temperature reaching 34.5°C on average across the flowering period, the rice plants showed spikelet sterility at 5.5%, 14.5%, and 21.8% in O-11, O-2, and F fields, respectively. The lower spikelet sterility in O-11 could be attributed to the slower decrease in the SPAD value, which was realized by higher soil fertility in O-11. The slower decline in SPAD value in O-11 could also have helped the rice plants to maintain the fraction of imperfectly filled grain which was comparable or smaller (20.4%) than that for F (28.9%). The poor performance of the plants in O-2 (25.4%) was ascribed to the earlier decline in SPAD value and commencement of lodging. Further studies are warranted into the mechanisms of reduced heat-induced yield loss under organic fertilizer management.