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农田防护林带具有庇护农田、促进粮食高产稳产的巨大作用。但在农田受益的同时,林带也有抑制附近农作物生长的作用。靠近林缘两侧附近的作物注意生长发育不良,农作物植株低矮、瘦弱,并表现不同程度的晚熟,造成减产,这种现象被称为林带胁地。这是树木与农作物争水争肥和树冠遮荫的结果。林带胁地的主要原因有两方面:一是根系向田间扩展,与农作物争肥。二是树冠遮阴,拦截了大量的太阳辐射能,减弱了光照的强度和光照时间,影响了光合作用。林带胁地范围一般在一倍树高左右,东西走向的林带,北侧林缘遮阴面积大,相当于林带树高的三分之一,变动在3.5——4.5米之间,遮阴时间长达9小时;南侧仅为林带高度的六分之一,遮阴时间也
Farmland shelterbelts shelter farmland, and promote the high yield and stability of the great role of grain. However, while the farmland benefits, the forest belt also has the effect of inhibiting the growth of nearby crops. Crops close to both sides of the edge of the forest are notorious for their poor growth and development. Crop plants are low and emaciated, with late-maturing performance to varying extents, resulting in reduced production. This phenomenon is known as threatening by the forest. This is the result of the struggle between trees and crops for fertilizer and tree shade. There are two main reasons for the threat of forest belt: First, the root system to field expansion, fight for crops and crops. Second, the canopy shade, blocking a lot of solar radiation, reducing the intensity of light and light time, affecting photosynthesis. Belt threatening range generally in about double the height of the forest, east-west forest belts, the north edge of the forest shade area, equivalent to one-third of the tree height of the forest, changes in 3.5 - 4.5 meters, shade time Up to 9 hours; the south is only one-sixth of the height of the forest, shade time also