一、绪言 祖国的社会主义建设正以万马奔腾之势一日千里地发展着,我国的广大农村在生产关系改变的基础上,生产力有了空前的提高。粮食增产的数字一日一新,稻米亩产已过六万斤,小麦亩产也已在七千斤以上。单位面积产量的提高是我国粮食和其它经济作物增产的一个主要方向。提高的 I. INTRODUCTION The socialist construction in the motherland is developing with great momentum in every passing day. On the basis of changes in the relations of production in the vast rural areas in our country, productivity has risen unprecedentedly. The number of grain yield increases day by day. The output of rice has exceeded six kilos per mu and the per-mu yield of wheat has reached more than seven kilos. The improvement of yield per unit area is a major direction for the increase of grain and other cash crops in our country. improved