北京郊区自一九七二年推广间作套种三种三收种植制度以来,复种面积扩大,粮食产量大幅度增长。据统计,一九六六至一九七一年京郊粮食产量平均每年递增3.3%,一九七二至一九七六年每年递增5.1%。一九七四年以来,京郊三种三收已占粮田的80%以上,粮食总产和单产均超过了历史上最高水 Since the implementation of the three cropping systems of intercropping intercropping in the suburbs of Beijing in 1972, the area of ​​double cropping has expanded and grain output has increased substantially. According to statistics, grain production in the suburbs of Beijing increased by 3.3% annually from 1966 to 1976, and by 5.1% from 1972 to 1976. Since 1974, three kinds of three harvests in the suburbs of Beijing have accounted for more than 80% of grain fields, with the total grain output and the unit output exceeding the highest in history