Study On Difference Of Deep Soil Water Use Characteristic Between Apple Orchards And Typical Ecological Plantation On The Loess Plateau

Since the implementation of the project of‘Grain for Green project'(GFGP),the Loess Plateau has achieved remarkable results in the management of soil erosion by constructing a large number of artificial ecological forests.According to statistics,as of 2012,the area of plantations on the Loess Plateau reached 7.47 million hm~2.At the same time,in order to cope with the problem of reduced farmers'income after the reduction of cultivated land,the government has actively guided the large-scale development of characteristic economic forests(fruits)-Apples.By the end of 2017,the orchard area reached 1.31 million hm~2.And the yield of apple exceeded 20 million tons,accounting for 57%in China.Apple has become the leading industry for farmers in the region.At present,the coexistence of plantation and apple orchard has become an important landscape feature of the GFGP on the Loess Plateau.Compared with plantations,apples are more affected by human activities.Large-scale development of apple will change the balance of the regional water cycle,exacerbating the contradiction between water supply and demand,and threatening the sustainable development of the apple industry.Deep soil water is the main water resource for the Loess Plateau vegetation to cope with drought,but its reserves are limited.And once consumed,it is very difficult to supplement.Compared with the main artificial ecological forest on the Loess Plateau,what is the difference between apple in the amount and rare of soil water consumption in deep layers?What is the difference between different climate zones?Answering these scientific questions has important scientific implications for understanding the impact of orchard expansion on regional water cycles and orchard field water management.In this study,the typical artificial arbor forest(Robinia pesudoacacia,),artificial shrub(Caragana korshinskii)and apple(Malus pumila)were used to study difference between the amount and rate of soil water consumption in deep soil by means of field experiment and integrated analysis.The main progress is as follows:(1)The study cleared the effects of land use type,climate and soil texture on deep soil moisture(200-800 cm)in the Loess Plateau.The deep soil water content in the four regions showed farmland>apple>korshinsk peashrub>black locust.Affected by climate(rainfall and evaporation)and human management measures,the deep soil water content is significantly lower in the semi-arid areas(Zizhou and Yan'an)than in the semi-humid areas(Changwu and Baishui).In addition,the correlation between the deep soil water and the fine root length density,clay,silt and sand reached a significant level(P<0.05).The specific performance is as follows:the deep soil water is positively correlated with the content of clay and silt,and negatively correlated with the long density of sand and fine root length density.(2)The study analyzed the deep water consumption characteristics and influencing factors of apple orchards and typical ecological forests in different climate regions of the Loess Plateau.In a semiarid region,we found no significant differences in the amount of soil water consumption in deep layers between the three vegetation types,but significantly higher the rate of soil water consumption in deep layers in apple orchards than in black locust and korshinsk peashrub plantations(P<0.05).It is because that orchards have the vigorous reproductive growth.In a short period of time,a large amount of deep soil moisture was consumed;In contrast,in a semihumid region,the amount of soil water consumption in deep layers was lower in apple orchards than in the plantations,but there was no significant difference between them in the rate of soil water consumption in deep layers in most soil layers.(3)The study cleared the zonal regularity of deep soil water use in the apple orchard of the Loess Plateau.The amount and rate of deep water consumption in deep layers of the apple orchard in the Loess Plateau increased from south to north.The amount and rate of soil water consumption in deep layers of apples in Zizhou,Yan'an,Changwu and Baishui ranged from67-588 mm and 7.4-73 mm/yr,respectively.And all appeared:Zizhou>Yan'an>Changwu>Baishui.Overall,apple orchard pose greater risks of exacerbating deep soil desiccation in the semiarid region than in the semihumid region.(4)Based on the integrated analysis method,study analyzed the differences in soil moisture utilization between apple orchards and typical artificial ecological plantations in different climate regions of the Loess Plateau.It is found that there are some differences in the utilization of deep soil water among in apple orchards,artificial arbor forests and artificial shrubs.In the semi-arid area,the amount of soil water in deep layers of apple orchard and artificial arbor forest and artificial shrub forest were not significantly different,but the rate of soil water consumption in deep layers was significantly higher than that of artificial arbor forest and shrub forest(P<0.05);in the semi-humid area,there was no significant difference between the amount and rate of soil water consumption in deep layers of the apple orchard and artificial arbor forest.Our results suggest that apple orchards pose higher short-term risks of severe deep soil desiccation than plantations in the semiarid region of the Loess Plateau.