Effects of Planting Density on Grain Yield and Quality of Rice Cultivars in Aomori Prefecture

Abstract

We evaluated the effects of low planting density on rice grain yield and quality under a cool climate. We grew two rice cultivars (“Tsugaruroman” and “Masshigura”) at three planting densities, 21.2 hills m^–2 (normal density), 15.2 hills m^–2, and 11.2 hills m^–2, four plants per hill, transplanting in mid-May and late- May, in four consecutive years (2010–2013) in Kuroishi, Aomori Prefecture. In both mid-May and late-May transplanting, there was no significant difference in the grain yield with the planting density. However, the difference in the grain yield between 11.2 hills m^–2 and normal density (21.2 hills m^–2) was larger in the plots with late-May transplanting in 2011 and mid-May transplanting in 2012 than in the other plots. The grain quality decreased with decreasing density in the plots with “Tsugaruroman” in 2012, but not in the other plots. The grain yield was significantly correlated with the numbers of panicles and spikelets per unit area. The ratio of 11.2 hills m^–2 to normal density in grain yield and spikelet number was positively correlated with the mean air temperature from 11 and 50 days after transplanting. This suggests that the difference in the grain yield between 11.2 hills m^–2 and normal density is influenced by air temperature during the vegetative stage, and that the grain yield in 11.2 hills m^–2 might be greatly reduced under low temperature conditions, due to the difference in the number of panicles and spikelets.