每年3～5月,常有长时间的阴雨、低温、寡照,秧苗生长缓慢、素质较差,移栽大田的季节延迟。秧苗在大田的营养生长期相应缩短,最易形成三类苗。而且人力畜力打紧,会造成防治苗期病虫害不及时等,均易使水稻形成三类苗。三类苗表现为:主茎分蘖少,最高苗数不足;植株矮小, From March to May each year, there are often long periods of overcast, low temperature and under-shoots, slow growth of seedlings, poor quality and delayed seasons of field transplanting. Seedlings in the field corresponding to the shortening of vegetative growth, the most likely to form three types of seedlings. Tight manpower and animal power will result in the prevention and treatment of pests and diseases at the seedling stage is not timely, are easy to form three types of rice seedlings. Three types of seedlings showed: fewer stems tillers, the maximum number of seedlings shortage; plant short,