On chilling tolerance of South-China double cropping super rice varieties(combinations) with chilling stress at initial heading stage;

Using ten early and late super rice varieties as the materials,the dry matter production characteristics of double cropping super rice were studied in field conditions.

Using two super hybrid rice combinations Luliangyou 996(early rice) and Ganxin 688(late rice) as the materials,the effects of different transplanting densities(D1~D4 for early rice and M1~M4 for late rice) on the population development and grain yield of double cropping super rice were studied.