关中灌区实行小麦、玉米一年两作,复种指数高。从收麦到种麦之间相距只有100—110天,活动积温2300—2400℃,是夏玉米需要积温的下限。若迟播,或秋淋低温往往灌浆不饱,影响产量。1979年全省有100多万亩玉米,因迟播遇后期低温,造成严重减产。玉米晚熱还影响后茬小麦的整地备耕和适期播种,这是形成低产三类麦田的主要原因。因此,解决两料争时矛盾,是进一步提高全年粮食产量的重要途径。小麦播期的伸缩性较大,而成熟期则较集中,早播与早熟期相关性不明显;夏玉米对播期反应敏感,而成熟期伸缩性较大,早播可以早熟早收。因此,争取夏玉米早播早 Guanzhong irrigation areas to implement wheat and corn two crops a year, multiple crop index high. From receiving wheat to wheat between the only 100-110 days, the active accumulated temperature 2300-2400 ℃, summer corn is the minimum temperature required. If late broadcast, or autumn pouring low temperature filling often unsatisfactory, affecting production. In 1979, there were over 1 million mu of corn in the province, which resulted in a serious decrease in output due to the late low temperature after late broadcast. Corn late heat also affects the preparation and proper sowing of stubble wheat, which is the main reason for the formation of low yield three types of wheat fields. Therefore, resolving the contradictions between the two materials is an important way to further raise the grain output for the year. The sowing date scalability of wheat is greater, while the maturity is more concentrated, early seeding and precocious correlation is not obvious; summer maize is sensitive to sowing date, while the mast is larger, early seeding can be early maturity. Therefore, early summer corn for early fight