Abstract:

In the eastern and southern districts of Sichuan Province, grain yields of hybrid midseason-rice varieties have been increased, but its grain quality remains very poor. In particular, the head rice percentage is low and chalkiness is high due to high air temperatures that occur 0 to 20 days after full heading. Although many studies have examined the effects of cultivation factors on grain quality, few improvements in grain quality have been made in these special districts. This paper explores the effect of super sparse cultivation on head rice recovery and chalkiness in hybrid rice varieties and provides a theoretical and practical basis for the cultivation of high quality rice. The experimental design consisted of three hybrid rice varieties (‘II you 7’,‘Shanyou 63’ and ‘Xiangyou 2’) planted at six different densities, where the hill was removed at full heading and N applied on different days after full heading in a randomized block design with 3～4 replications. Using analysis of variance and correlation analysis, the results indicated that there were highly significant negative correlations between planting density and the percentage of head milled rice and highly significantly positive correlations between plant seedling density and the chalky percent. When super sparse cultivation was at 7.51×104 hill•hm-2 with 150-210 kg N•hm-2, the grain yield was equal to CK (21.64×104 hill per hm2 with 150 kg N•hm-2), but the percentage of head milled rice increased by 15.69% to 22.92%, and the chalky percent decreased by 16.34% to 21.22%. The increase in grain quality in super sparse cultivation was due to an increase in the number of spikelets per panicle, a decrease in the weight of leaf per grain at full heading, and reduced grain filling rate; hence, the percentage of head milled rice and chalkiness were improved. Additionally, the seed setting rate and the percentage of head milled rice in super sparse cultivation were increased by applying N 20 days after full heading.