华北雨量很少,而且大都集中在7、8月间。4、5、6三个月时常苦旱,作物之所以能够生长,并得到一定的收获,主要靠了土壤中预光保存下的水分。关于这个问题,Alwaye 曾做过如下的试验:他用高6呎镀锌的铁筒(有底),尽可能的把土按自然状态的结构装到筒里去,然后按这个土壤的保水力,加入充分的水。把曾经发芽的春小麦种子,播在湿土的表面,然后盖上一吋厚的干土,以防止蒸发。以 Rain in northern China rarely, but mostly concentrated in July and August. 4,5,6 three months often drought, the crop has been able to grow, and get some of the harvest, mainly rely on the soil pre-stored under the water. On this issue, Alwaye has done the following experiment: he used 6-foot-high galvanized iron tube (bottom), as far as possible the natural state of the soil structure into the tube, and then press the soil water retention , Add enough water. Sow the once spring wheat seeds on the surface of wet soil and cover with an inch of dry soil to prevent evaporation. To