This is mainly due to the improvement of rice varieties , including ( 1 ) the development of semidwarf rice varieties suitable for mechanical harvesting , ( 2 ) the development of varieties resistant to lodging resulting from heavy fertilizer applications , ( 3 ) the development of varieties resistant to diseases and insects , ( 4 ) the establishment of a good seed propagation system , and ( 5 ) the rapid renewal of rice varieties through the services of the rice nursery centres 主要是改善了水稻品种，这包括： 1 ）选育半矮化品种，有利于机械收割； 2 ）选育抗倒伏品种以适应高施肥量； 3 ）选育抗病虫害的品种； 4 ）建立良种繁殖基地； 5 ）通过水稻育苗服务中心，及时更新品种。
