土壤这一极其重要国土资源不但在数量上不能轻易被吹跑或冲掉,而且必须在质量上予以保护与改良,使之更适于植被、作物、牧草或林木的生长。我国祖辈劳动人民,创造了绿肥和作物轮作以及粪肥还田的妙法,使土壤中的有机质和氨磷钾维持不坠,从而使耕种了好几千年的土壤仍然有肥力。和我国历史同样悠久的埃及古国,几千年前拥有地中海南岸非洲北部广阔的肥沃土地,赖以立国。不幸的是他们并没有创造出像我国祖辈那样一套使土壤肥力维持不坠的 Soil, an extremely important land and natural resource, can not easily be blown off or washed away in quantity and must be qualitatively protected and improved to make it more suitable for the growth of vegetation, crops, pastures or trees. The working people of our ancestors in our country have created the wonderful method of turning green manure into crop rotation and returning manure to soil so that the organic matter and phosphorus, potassium and phosphorus in the soil will not fall. As a result, the soil that has been cultivated for thousands of years remains fertile. As the ancient Egyptian country, which has the same history as our own, has a vast fertile land in the northern part of Africa on the southern bank of the Mediterranean thousands of years ago, and has thus established itself as a nation. Unfortunately, they did not create the kind of soil fertility that their ancestors did