Research On Optimal Belt Spacing Of Farmland Shelterbelt Network In Southern Xinjiang

The arid and semi-arid area in southern Xinjiang has a large area and a wide range,which is a serious disaster area affected by severe wind and sand disasters.With the development of agricultural intensification,mechanization and refinement in southern Xinjiang,on the one hand,with the annual growth of the age of the shelterbelt belt,the structure of the shelterbelt in most areas has been damaged in varying degrees;on the other hand,the shelterbelt network has affected the development of large machinery The structure of the forest belt is seriously damaged due to the lack of water diversion and irrigation.In recent years,scholars at home and abroad have done a lot of research on the scale permeability of single shelterbelt,effective shelterbelt distance and tree species collocation,but less on the analysis of shelterbelt spacing under the synergistic effect of multiple shelterbelts in farmland shelterbelt network.The existing problems in local farmland shelterbelt network can be effectively improved and the land threatening effect of shelterbelts can be reduced by reasonable shelterbelt configuration and spacing.Therefore,this study selected the typical jujube field Shelterbelt of 224 regiment in Hotan area of Southern Xinjiang as the research area.Through field investigation and observation,the structure factors of the shelterbelt,the wind speed before and after the shelterbelt,the wind tunnel simulation experiment and the theoretical model of porosity calculation were carried out to explore the protection effect of different spacing under different farmland shelterbelt configurations,and the most suitable spacing configuration of the shelterbelt in the study area was selected,It provides theoretical basis and practical reference for the renewal and construction of farmland shelterbelt network.The main conclusions are as follows:(1)Most of the farmland protection forest belts in the study area are configured with 4rows of forest belts,which can effectively prevent wind damage from destroying farmland crops under the conditions of strong wind events.The results of field observation show that the average wind speed at the height of crops in the forest network is only about 4 m/s when the wind speed in the field reaches 16 m/s.(2)The results of field observation show that the optimal permeability is 32%.The wind tunnel test results show that the wind speed changes significantly under different forest belt permeability.Under the wind speed of 12 m/s,the wind speed of the forest belt with different porosity can recover to about 6 m/s below the tree height at the horizontal distance of 20 h.Based on the field observation data and wind tunnel simulation data,the physical model of forest network scale permeability was constructed.The results showed that the optimal permeability of the shelterbelt was 32%,that is,four rows of shelterbelt were set according to the existing tree species in the study area.(3)In the shelterbelt of jujube field,the target crop jujube has obvious windbreak ability.Through the wind tunnel simulation test with and without afforestation,the results show that the windbreak effect of jujube forest with different forest belt rows is between 87% and 90%,which indicates that the tall target crop should be considered in the construction of shelterbelt network.(4)Through the analysis of wind speed profile of the forest network,it is found that the wind speed gradually decreases after the airflow passes through the farmland shelterbelt network under the collaborative configuration of multiple forest belts,and the speed of wind speed decreases gradually,and finally tends to be stable,in which the decline range from 0 h to 30 h is the largest,indicating that the primary forest and the first two field forest belts play a very important role in the whole forest network.(5)Based on the field observation data and the wind tunnel simulation test data of forest network,the regression model of the optimal forest belt spacing was established.The results showed that when the maximum wind speed was 14 m/s in the study area,the base forest could be set at 14 rows,the field forest belt could be set at 4 rows,and the forest belt spacing could be set at 14 h,that is,the optimal forest belt spacing was 140 m ～ 175 m.Through field observation,wind tunnel experiment and theoretical model of multi forest belt porosity calculation,the most suitable forest belt spacing configuration in the study area can be obtained,which can reduce the occupation area of farmland shelterbelt network,reduce the land threatening effect brought by the forest belt,and reduce the water cost of shelterbelt,especially in the extreme arid area of Southern Xinjiang where water is the main constraint factor At the same time,it also promotes the rapid development of agricultural refinement and mechanization.