| The construction of farmlands shelterbelt system and conservative tillage measures are important means of controlling wind erosion of farmlands soil in drylands.The existing research on farmlands shelterbelt structure focuses mainly on the porosity,and mostly takes the trees with complete canopy structure as the objects.While few studies on different configurations of deciduous shelterbelts with the same porosity were conducted.Meanwhile,due to the poor climatic conditions of drought,water shortage,and severe wind erosion in drylands,the effects of single control measure to restrain soil wind erosion is limited.Therefore,it is of great significance for alleviating wind erosion disaster of farmlands in drylands to explore the structural factors affecting shelter effects of farmlands shelterbelts,evaluate the shelter effects of farmlands shelterbelts of different structures,further optimize the structure of farmlands shelterbelts and enhance the integrated shelter effects of farmlands shelterbelts and conservative tillage.In this study,a wind tunnel study was conducted to analyze the shelter efficiency and effective protection area of arbor and arbor-shrub mixed farmland deciduous shelterbelts with different structures of 2-row-1-belt pattern for rain-fed and oasis farmlands.Through a field control experiment,the soil improvement and wind erosion protection effects of stubble(15 cm)and straw mulching(2000 kg/hm~2)measures were calculated,compared with the bare field control,were estimated.Research indicates:(1)For rain-fed and oasis farmlands shelterbelts with different structures,the shelter effects of the arbor-shrub mixed shelterbelts are better than those of the pure arbor shelterbelts.For the arbor-shrub mixed shelterbelts,as the porosity is the same,the shelter effects of the shelterbelts with arbor-windward-shrub-leeward(A-S)mode are better than those with shrub-windward-arbor-leeward(S-A)mode.For the A-S shelterbelts with a relative low porosity of shrubs,the overall shelter effects does not change significantly with the change of arbor porosities.That is,as the overall porosity of the shelterbelts increases,the shelter effects does not change significantly.(2)The optimized structure of shelterbelts for rain-fed farmlands is:the Ulmus-Caragana mixed mode,in which the Ulmus plant spacing is 6 m,the Caragana plant spacing is 2.25 m,and the row spacing is 6 m.The optimized structure of shelterbelts for oasis farmlands is:Populus-Caragana mixed mode,in which the Populus plant spacing is 3.75 m,the Caragana plant spacing is 2.25 m,and the row spacing is 3.75 m.(3)In this study,the soil moisture of the 3 different tillage measures was low,and no siginificant change was observed after a wind season(from Oct.to the next April).Compared with before the wind season,the soil bulk density of bare field was significantly reduced,the measures of residual stubble increased significantly,and straw mulching measures did not change obviously.The soil organic matter of the mulching measures was significantly higher than the other two measures(P<0.01).After a wind season the soil organic matter increased in different measures,while the difference among different tillage measures was not significant.After a wind season,the hydrolyzed nitrogen and available phosphorus in bare field decreased,the available potassium did not change significantly,while the 3 soil nutrients in the 2 conservative tillage measures all increased to different degrees.Compared with the bottom soil,the topsoil of the farmlands showed a certain coarsening trend under different tillage measures.Compared with the bare field,the 2conservative tillage measures had a certain effect on preventing soil wind erosion and dust release.(4)In this study,it is difficult to reduce the average wind velocity of farmlands for sand transportation to the threshold wind velocity(5 m/s)of the wilderness for sand transportation by using the two conservative tillage measures alone.For rain-fed farmlands,the optimized shelterbelt×stubble and shelterbelt×mulching can increase the threshold wind velocity of the protected area for sand transportation to 7.25 m/s and 6.67 m/s.For oasis farmlands,the optimized shelterbelt×stubble and shelterbelt×mulching can increase the threshold wind velocity of the protected area for sand transportation to 8.20 m/s and 7.46 m/s.The integrated protection capability of the protection system can be effectively improved by combining farmlands shelterbelts with conservative tillage measuresIn this study,the influence of different structural factors on the shelter effects of farmlands shelterbelts was systematically analyzed with the shelterbelts structure optimized,and the effects of soil improvement and wind erosion prevention of different conservative tillage measures were discussed.In this study,a integrated protection technology of soil wind erosion of farmlands combined with shelterbelts and conservative tillage in drylands was proposed and its shelter effects was evaluated,providing the theoretical basis and practical reference for the construction of integrated soil wind erosion control system in drylands... |
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