Effects Of Typical Agronomic Measures On Soil Moisture And Jujube Growth In Drying Farming Mountain Jujube Plantations In Hilly Loess Plateau Regions

Drought and water shortage are key limiting factors for agricultural development in hilly China's Loess Plateau.Very deep groundwater make precipitation become the only water source for local vegetation growth.This region had complex gully topography,which suffering from serious soil erosion,and thus the government have taken some vegetation restoration projects.However,with the increase of vegetation coverage,it's hardly to maintain their normal growth in rain-red conditions,resulting in the gradual depletion of deep soil moisture and the formation of dried soil layers?DSLs?.Jujube?Ziziphus jujuba Mill.?is the native tree species with strong drought resistance.Dried soil layers were also appeared in jujube plantations,which brings hidden dangers for jujube growth.In view of the common problems of dried soil layers,dwarf and densely mountain jujube plantations in Mizhi county of north Shanxi province were used for test trees in this study.Based on long-term field positioning experiments,the effects of several typical agronomic measures,such as mulching,pruning,and mulching with pruning,on soil moisture and jujube growth were studied,in order to explore a new method for improving the water use efficiency of jujube plantations in hilly China's Loess Plateau region,and expected to provide technical support for dried soil layers management and sustainable development of jujube plantations.Meanwhile,it can also provide referential theoretical and technical basis for prevention of deep dried soil layers and sustainable development of artificial forestland in the Loess Plateau.The main conclusions are as follows:?1?Compared with bare land?CK?,both white plastic film?T₁?and ground cover mulching?T₂?effectively improved soil hydro-thermal conditions.The average soil moisture?0⁵0cm?for T₁ and T₂ was 16.7%,16.5,respectively,which increased by 3.9%and 3.7%respectively compared with CK,but had no significant difference between T₁ and T₂?P<0.05?.T₂ had the best effect on rising soil temperature in winter,the average soil temperature?0⁵0cm?increased by 0.5?and 0.8?respectively compared with T₁ and CK;while T₁ had the best effect on rising soil temperature in spring,summer and autumn,the average soil temperature?0⁵0cm?increased by 0.5?and 0.9?respectively compared with T₂ and CK.The warming effect of mulching delayed the freezing time and advanced the melting time of different soil layers,thus shortening the whole freezing-thawing time.Compared with CK,the freezing-thawing time was shortened by 7¹1 days in T₁,while 3⁴days in T₂.In conclusion,T₂ not only had slightly lower soil moisture than T₁,but also effectively controlled soil temperature maintaining stable change.Meanwhile,T₂ has the characteristics of low cost,long service life and can prevent the growth of weeds,thus it is more suitable for the management of dry farming mountain jujube plantations.?2?Compared with regular pruning treatment?CK?,light?C₁?,medium?C₂?,and high pruning?C₃?measures both improved soil moisture.The average soil water storage?0³00cm?during 2012-2015 jujube growth period in C₁,C₂,C₃ increased by 6.2¹8.2mm,14.3⁴0.0mm and 24.2⁶3.2mm,respectively,compared with CK.Pruning reduced soil water deficit amount or degree,but increased available soil water supply.The average rainfall was higher than the average annual rainfall of the study area.If calculated according to the average annual rainfall,the change of soil water storage in CK,C₁,C₂ was-58.8mm,-38.7mm,-11.8mm,respectively,resulting in soil water deficit,while it was 8.6mm for C₃,resulting in soil water supply.?3?Leaf size,number of shedding shoots,and fruit specification increased,while the ratio of number of leaf and fruit decreased with the increase of pruning intensity,indicating that pruning can inhibit jujube vegetative growth and promote the reproductive growth.Compared with CK,the yield was increased,but water consumption was decreased both for C₁,C₂,C₃.Both taking yield and water consumption into consideration,the increase in pruning intensity increased the water use efficiency?WUE?.The WUE in C₁,C₂,C₃ was1.0¹.2,1.0¹.3,1.2¹.6 times than that of CK,respectively.C₃ not only had the highest average soil water storage,and can reach positive soil water balance,but also had the highest water use efficiency,and can obtain considerable yield(the annual yield in four years is about 9000 kg ha^-1).Meanwhile,considering the dried soil layers has appeared in jujube plantations,we recommend C₃ as the optimal pruning measure for dry farming mountain jujube plantations.?4?After one dry and three rich rainfall years,soil moisture in deep soil layer was improved at various degrees for mulching with pruning?PM:ground mulching+high pruning?and regular pruning treatment?CK?with the improvement depth of 480cm and 260cm,respectively.Degree of soil drying in 200-500cm soil layer for PM had changed from grade2 severe level to grade 1 severe level,while was still at grade 2 severe level for CK.?5?Mulching with pruning measure is a good agronomic technology in the dry mountain jujube plantations,which can reduce soil evaporation and vegetation transpiration water consumption at the same time,and greatly decreased soil water loss,thus ensuring the survival of trees in dry environment.This agronomic measure can not only adjust jujube growth,increase jujube yield,reduce jujube water consumption,but also improve the water use efficiency(PM:2.05².28 kg m^-3;CK:1.59¹.79 kg m^-3).It effectively controlled the soil drying,which was expected to achieve the sustainable management for dry farming mountain jujube plantations.