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农作物在其生长发育期间,对土壤水分的要求不是固定不变的。例如各种农作物种子的膨胀、发芽和幼苗形成期,水分供应主要来自0—10厘米耕作层。若该层有效水分含量仅在5—10毫米,则种子的发芽、出苗就大受抑制;若有效水分含量大于20毫米,就能保证农作物的正常出苗。在穗和花的形成期,100厘米土层的有效水分含量低于80毫米,就不能保证农作物的正常生长和发育;只有当有效水分含量为100—200毫米时(占田间最小持水量的60～100%),农作物才能获得正常的生长和发育。
During crop growth and development, the requirement for soil moisture is not constant. For example, the expansion of various crop seeds, germination and seedling formation period, the water supply mainly from 0-10 cm farming layer. If the effective moisture content of the layer is only 5-10 mm, the seed germination, emergence is greatly inhibited; if the effective moisture content greater than 20 mm, we can ensure the normal crop emergence. In the formation of spike and flower, the effective moisture content of 100 cm soil layer below 80 mm, can not guarantee the normal growth and development of crops; only when the effective moisture content of 100-200 mm (accounting for the field minimum water holding capacity of 60 ~ 100%), the crop can get the normal growth and development.