我们种庄稼,通常是把肥料施在土壤里,然后被作物根系吸收利用。在无土培养时(水培、沙培),则是把营养元素按比例溶解在水中供作物根系吸收。作物的根外营养则不同,它是通过叶片和嫩枝吸收营养物质。人们通常按照作物生长发育状况,把营养元素配成一定浓度的溶液,喷布在植株茎叶上。植物的根外营养有很多优越性:(1)可以大大节约肥料。少量肥料施在土壤里,往往被土壤吸附固定,使作物不能吸收利用,如果喷在植株上,特别是喷施微量元素作追肥,起的 We grow crops, which are usually applied to the soil and then absorbed by the crop roots. In soilless culture (hydroponics, sand culture), it is the proportion of nutrients dissolved in water for crop root absorption. The nutrition of the crop differs from that of the root, in that it absorbs nutrients through leaves and shoots. People usually according to crop growth and development, the nutrient elements dubbed a certain concentration of solution, sprayed on the plant stems and leaves. There are many advantages of plant root nutrition: (1) can greatly save fertilizer. A small amount of fertilizer applied to the soil, often by the soil adsorption fixed, so that crops can not be absorbed, if sprayed on the plants, especially the application of trace elements for topdressing, starting