53.什么是有效土层和制约土层?设施灌溉中所说的有效土层,是指达到了24小时田间持水量之后,通过土面蒸发、作物根系吸收消耗和毛管水补充等方式消耗土壤水分所达到的土层深度。这个深度随着干燥期的拉长是会加深的,所以,一般以灌水间隔日数作为连续干燥天数。设施栽培中,有效土层的深度一般都取40—50厘米深。所谓制约土层,是指在有效土层内,对土壤水分消耗起支配作用最大的土层。就是说,这个土层在灌水后水分消耗最大最快,经过灌水间隔日数的连续干燥后,这层土壤的水分已下降到接近生长阻滞湿度,水分的减少变得比其它层次小,土壤水分的消耗向更下一层推进。制约土层也就是根群分布最多吸水最厉害的层次。设施栽培由于经常灌水,作物根系主要分布在浅层,所以,大多数情况下表层的20厘米左右是制约土层。把负压计的陶瓷头埋在10—16厘米深处, 53. What is the effective soil layer and the constraints on the soil layer? The effective soil layer in the irrigation of the facilities refers to the soil that has been consumed by soil evaporation, crop root absorption and capillary water replenishment after reaching the 24-hour field capacity Depth of soil reached by moisture. This depth will be deepened with the extension of the drying period, so the number of irrigation intervals is usually taken as the number of consecutive drying days. Facilities cultivation, the depth of effective soil generally take 40-50 cm deep. The so-called constraints of soil, refers to the soil within the effective soil layer, the dominant role of soil moisture consumption from the soil. In other words, this soil layer after water irrigation water consumption maximum and maximum, after the continuous interval of irrigation days dry, the soil moisture has dropped to near growth retardation humidity, water reduction becomes smaller than the other levels, soil moisture The consumption to the next level. Restriction of soil layer is the most root distribution of water absorption most powerful level. Planting As the regular irrigation, crop roots are mainly distributed in the shallow, so in most cases about 20 cm of the surface layer is constrained. The negative pressure of the ceramic head buried in 10-16 cm deep,