The long historical unit grain yields in Guyuan were analysed by using single factor s muti-times regression, and muti-factors regression, the variation features of unit yield in recent 30 years and thier relationships with the associated factors were also analyzed. The results show that:① The variation classed into three stae: In mid-late 60 s nit yield variated around 450-750kg/hm2, with technique r retrogression and unfitable climate. In 70 s ̄80 s, unit yield fluctuated around 750-1 200kg/hm2, with some ...
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