Abstract: Sky diffuse radiation in shelterbelt-crop intercropping system has been calculated and measured. It is found that the "light threatened area" is only in a range of 1—2 times the height of shelterblt trees, within which, crop production is reduced. The effect of shelterbelt on sky diffuse radiation at the distance of 30H can be neglected. The relationship between mean relative radiative intensity and distance from shelterbelt conforms with Logarithm curve, with the maximum increasing rate appeared at 3-4H. North-south direction shelterbelt exerts less effect on sky diffuse radiation than east-west one. The minimum range of "light threatened area" and the range of maximum wind speed reduction are important parameters in shelterbelt network size designing.

Key words: maize straw, Zn fertilization, form, bioavailability, calcareous soil