2017 Volume 86 Issue 2 Pages 129-138
In Hokkaido, dense planting of rice has been recommended to keep a higher percentage of whole grain (PWG), but sparse planting is demanded to save labor and cost. A field experiment of sparse planting was conducted in NARO Hokkaido Agricultural Research Center from 2013 to 2015. Rice cultivar “Nanatsuboshi” was transplanted with 30 cm row spacing at 4 levels of hill spacing and 2 levels of seedling number per hill (SNPH). Temperature in cropping season was higher than in an average year in all of the 3 years, but reduced SNPH resulted in lower grain yield due to lower percentage of ripened grains than standard SNPH. Wider hill spacing did not reduce the yield significantly, but tended to decrease PWG. Spikelet number per panicle (SNPP) was negatively correlated with PWG, and the PWG was lower than 70% when SNPP exceeded 70 under a low temperature condition at the grain-filling stage (cumulative mean temperature at 40 days after heading was lower than 800°C). In standard SNPH, SNPP with 22 cm hill spacing was 70.7. Therefore, to maintain more than 70% PWG, hill spacing should not be wider than 22 cm.
