| Farm-shelter forest was one of the important contents about forestry ecological engineering construction in irrigated area of Gansu Jingtai. The construction of farm-shelter forest contributed to defending against natural disasters of agriculture, improving micro-climate conditions of farmland and moisture condition of soil, creating suited environment for crops growing, ensuring agricultural production of district. Meanwhile, farm-shelter forest construction also brought about some negative effects, such as crops contending with forest belt for water and moisture threatening.In the study the field and laboratory methods were united. The soil evaporation and soil moisture of oasis farm-shelter forest system in Jingtai irrigated area were researched. The preliminary conclusions were as follows:(1) In system the soil water evaporation firstly increased and then decreased after irrigation, and the soil water evaporation in system was more than that of the control site. Before irrigation in forest network the soil water evaporation on average was lower 62.35% than that in the control site. On the fourth day after irrigation the soil water evaporation in forest network on average was lower 45.84% than that in the control site. On the sixth day shelter network was lower 29.68%, On the tenth day forest network was lower 39.86%, These showed that the farm-shelter forest system in oasis could effectively reduced soil evaporation.(2) Soil evaporation showed variation on the different forest belt ldistances in farm-shelter forest system. The minimum of soil water evaporation emerged around the 1.0H.. The nearer the distance was ,the more soil evaporation was, but in 1.0～3.0H the farer the distance was , the more soil evaporation was. That was to say, Soil evaporation in forest network firstly decreased and then increased.(3) In the different stages of the crops growing, soil evaporation showed differences in system. The soil evaporation before crops drawing leaves was higher 36.72% than after crops drawing leaves. The evaporation in system above 1.00mm/d accounted for 37.14%. But evaporation in system above 1.00mm/d only accounted for 17.14% after crops drawing leaves, and the soil evaporation accounted for the secondary corporation.(4) Soil moisture appeared disciplinary changes on vertical direction in farm-shelter forest system. The soil moisture approximately showed tendency of"high-low-high"before and after crops drawing leaves. The moisture in soil surface layer 0～20cm was higher than that in the 20～40cm. The mean soil moisture only was 6.69% in the soil layer 20～40cm. In the layer 60cm mean soil moisture increased and came to 8.41%. In a word, the life actions of crops root system and characteristics of soil texture were the main causes of vertical changes about the soil moisture in farn-shelter forest system.(5) Soil moisture showed the trend of"low-high-low"with the increasing of forest belt distance on level direction in farm-shelter forest system. Soil moisture evidently was not enough around the distance 0.3H from the forest belt leeward. Filed moisture gradually increased with the increasing of distance in the range of 0.3～1.5H. These indicated forest belt contending with crops for water mainly happened within the distance 0.3H.(6)Soil moisture showed obvious differences on the different positions of forest belt leeward silde. The mean soil moisture was the highest on the distance 1.5H and came to 11.30%; At 0H the mean moisture was the lowest and only was 6.84%. These indicated within 0.3H forest belt contending with crops for water was intense, and in this area soil moisture clearly was not enough.(7) In the different stages of crops growing, the mean soil moisture in the soil layer 0～60cm nearly appeared parabola form with the forest belt distance changing. The regression equations between soil moisture and forest belt distances before and after crops drawing leaves were as follows: SM(X)=6.643-0.653X-1+2.329X R2=0.7333 SM(X)=6.334-1.013X-1+3.472X R2=0.5650(8) In system the soil moisture and soil evaporation correlation changes were rightly opposite within the distance 0.3H from the forest belt leeward, but in 1.0～3.0H these changes were nearly consistent. Those showed soil moisture and evaporation variation were closed related to the wind-break effect of forest belt and the growth situation of crops in forest network.(9) In system atmosphere temperature, relative atmosphere moisture, wind speed, solar radiation and soil moisture had certain effects on the soil evaporation. The influence degree order of these factors was: soil moisture﹥solar radiation﹥relative atmosphere moisture﹥wind speed﹥atmosphere temperature(10) Soil moisture showed high negative correlation with the wind speed. On the contrary, the correlations among soil moisture, atmosphere temperature, relative atmosphere moisture and solar radiation were not evident.
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