| In order to explore the deep soil desiccation actualities and possible solutions of apple orchards in Weibei dryland,we carried out relevant research from three aspects.1)Soil moisture deep to 15 m belowground were measured twice for 5 apple orchards with different planting year and density in 2008 and 2015,respectively,change of soil water content during growth season and effects of rainfall on yields in these orchards were also be compared.Therefore,we can analyze the period of occurrence of soil desiccation and the optimal time to adopt corresponding method.2)Total water consumption of 2-year old apple trees were measured by sap flow instrument and weight method from April to October in 2016,the conclusion would be a reference to increase the water use efficiency of local apple orchards.3)The effects of five different mulching treatments on soil water content from April to September and the fruit quality were mearsured,in order to provide scientific soil management method for local apple orchards.The main research results were as followed:1?Soil profile consist of black loessial soil,loessal soil and red clay soil in Weibei dryland.Among them,the positive effect of red clay soil that located at the 9~11m layer on the upper soil water storage is obvious.When water storage in red clay soil was sufficient,this layer could made up water deficit of the upper soil.However,when the water consumption in this layer declined to wilting humidity,soil water transfer limited to 11 m underground because the soil drying-layer appeared.2?the soil desiccation index(SDI)measured in 2008 for 5,10,15,20 and 25 a were 6.46%,32.68%,37.65%,63.33% and 62.81%,while SDI for the same orchard 7 years later were 35.98%,59.65%,42.21%,75.06% and 70.09%,respectively,indicated that the longer the planting year was,the higher the SDI was.In addition,the degrees of soil desiccation were quickly from 5 to 12 a and 10 to 17 a,the increasing proportion per year were 4.22% and 3.85% averagely,but slowly from 20 to 27 a with an increasing proportion of 1.7%.The soil desiccation of 5 a apple orchard was slight and the soil moisture was close to cropland,and after planting 15 a,the soil desiccation spread to 11 m belowground(paleosol layer),and to 17 a,the buffer function of paleosol layer was lost and if the rainfall in a year cannot meet the water consumption of apple trees,the quality and yields would be limited by and linearly dependent on annual rainfall.3?Thinning could slow the soil desiccation process.The orchards with a planting density of 4 m×6 m(15 a,25 a)had significantly lower rates of soil desiccation during 7 years,with an average of 0.65% and 0.61% per year,respectively.The soil desiccation index of 22 a orchard was 42.21%,which was 17.44% and 32.85% less compared to orchards of 17 a and 27 a,respectively.In addition,the soil moisture of 2~5 m layer with thinning treatment was higher than the nonthinning treatment,indicating orchards with lower density could compensate soil water in deep layer by rainfall in a wet year.However,in a dry year,even for the orchard with lower density,the water consumption of trees would be inevitable to be compensated by deep soil water,which was more common in old orchard,and thinning can only delay the formation of soil dry layer.Therefore,this study suggested corresponding measures should be taken around 12 a after planting,before the soil desiccation expanded to the paleosol layer.4?The total consumption of water of 2-year old apple tree was 34.0kg,and the water supplement by weight method was 38.1kg.The order of the monthly water consumption was: May> April> June > July> October> September> August,which in June and September the growth rate of young trees was higher.Combined with the local rainfall law,the article considered that water-saving measures and irrigation should be carried out in May and June.5?The soil water content of different mulching in 0~1m soil layer in Luochuan was significantly increased during rainy season,the increase degree in 0~0.6m soil layer of control group higher than other mulching treatments,but under 1m,the soil water content of control group was lower than others,it shows that soil water content in 0~1m soil layer was greatly influenced by rainfall.Rainfall collection+black film mulch treatment was contributed to the storage of soil water below 1m soil layer,the effect of straw mulching on soil moisture content below 1.6m soil layer was significant,while black film and black ground fabric mulch could ensured surplus of rainfall per year in 6-year old apple orchards.6?The effects of mulching treatment on apple fruit quality increase was positive.The average fruit weight under black mulching treatment was 286.82 g,which was the highest in five treatments;The soluble solids under black film mulch and rainfall collection + black film mulch were 12.52% and 12.64%,respectively,and the average yield per tree were 16.41 kg and 18.13 kg,respectively.Both of soluble solids and yield were ranked at top two in five treatments.The titratable acidity of the apple fruit under the straw mulch treatment was lower and the carpopodium length was higher than other treatments,this may be related to its biological coverage to promote soil microbial activity and improve nutrient use efficiency.There was no significant difference between the fruit shape index and fruit surface coloring in five treatments. |
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