Ecological And Hydrological Processes And Simulation Of The Jujube Agroforestry System In The Loess Hilly Region

The intercropping compound system has the effects of changing the soil microenvironment,preserving soil moisture,reducing soil evaporation,and changing the microclimate of the system,but it also has problems of excessive water consumption and water competition.However,the feasibility study of implementing intercropping compound management in dryland orchards is weaker.In the loess hilly region,precipitation is the only source of agriculture and vegetation growth.The long-term plowing management of rain-fed jujube gardens has caused serious problems such as land degradation and soil erosion,affecting the economic benefits and ecological functions of jujube gardens.Therefore,in this study,economic crop canola and daylily were introduced into the rain-fed jujube orchard in the loess hilly region,and two types of intercropping system were constructed.Through continuous monitoring of soil moisture,orchard evapotranspiration,and fruit tree growth for 4 consecutive years,as well as soil physical and chemical characteristics and fine root distribution and other determinations were conducted to systematically study the effects of intercropping of red jujube forests on the physical and chemical characteristics of the orchard soil,root system distribution,profile soil moisture,and orchard transpiration dynamics,and evaluate the water use status and ecological benefits of the two intercropping complex systems.?1?The effects of crop intercropping on the soil quality of the jujube forest complex system were clarified.Compared with the control,under the canopy of jujube trees,the field water holding capacity of canola treatment and daylily treatment soil increased by 3.4%and 2.3%respectively;soil available phosphorus content decreased by 31.7%and 33.4%respectively;soil cation exchange increased by 28.6%and 17.0%.Between rows,the soil bulk density of canola treatment and daylily treatment decreased by 5.5%and 2.9%respectively;soil field water holding capacity increased by 11.9%and 9.4%respectively;soil saturated hydraulic conductivity increased by 29.1%and 27.2%respectively;soil available nitrogen respectively Increased 167.0%and 78.7%;soil organic carbon content increased by 53.4%and 36.1%respectively;soil cation exchange capacity increased by 12.3%and decreased by 3.9%,respectively.?2?The synergistic relationship between soil water regulation effect and inter-species water competition in the jujube forest intercropping complex system was proved.Under the canopy of the jujube tree,the soil moisture content in the 0-60 cm soil layer of the two intercropping systems was significantly higher?p<0.05?than the control treatment.Between rows of jujube trees,the soil moisture content of the two intercropping systems and the 0-60cm soil layer was significantly higher during the study period?p<0.05?than the control treatment;but the soil moisture content of the 60-180 cm soil layer of the daylily intercropping composite system was significant.Low?p<0.05?in the control treatment,and the compound system of feed and rape intercropping was significantly lower than?p<0.05?in the control during 2015-2017.A soil water relative differential index?SWDR?was constructed to determine the occurrence and strength of soil water competition.There was no significant soil water competition between jujube trees and canola during the study period,while serious differences existed between jujube trees and daylily.Water competition:Among them,the average SWDR of 0-60 cm soil layer changes within-5.0%,the competition is weak,the average SWDR of 60-120 cm soil layer exceeds-5.0%,and the competition is strong.Within four years,the amount of change in soil water storage??W?was-23.9%below the canopy,which was-8.8%lower between rows;in the two years after the drought year,the soil water storage in each treatment had recovered,and two intercropping systems.The soil water storage recovery rate?5.8%?was faster than the control treatment?4.8%?.?3?The effects of crop intercropping on the root distribution and dried soil layer of jujube forest were clarified.Compared with the control,under the canopy of the jujube tree,the density of fine roots and roots of jujube trees in the two intercropping systems increased significantly in the 0-60 cm soil layer;between rows,the density of fine roots and roots of jujube trees in the canola treatment was 0-60 cm.The soil layer increased significantly,and in the daylily treatment,the fine root length density of jujube tree in 0-60 cm soil layer decreased significantly,but the fine root density of jujube tree in 120-300 cm soil layer increased significantly.The dry layer of soil under the canopy and interrow of jujube trees was reduced by 50 cm and 62.5cm in depth compared with the control;the daylily treatment only reduced the interlayer dry soil,and its depth was 65 cm.?4?The influence of crop intercropping on water consumption of jujube trees was proved.The transpiration of jujube trees treated with canola and daylily increased by 22.0%and 20.9%compared with the control treatment within four years.In dry years,the transpiration rate of jujube trees in each treatment was significantly suppressed from June to July,but the average transpiration rate of the intercropping system(1.2 mm d^-1)was higher than that of the control treatment(0.9 mm d^-1).Saturated water pressure deficit?VPD?,transpiration variable?VT?,and total radiation?R_S?are important meteorological driving factors for the transpiration rate of jujube trees.Compared to the control,the transpiration rate of jujube trees under canola and daylily treatments responded to meteorological factors.The threshold was higher.The soil water storage in 0-60 cm soil layer significantly affected the transpiration of jujube trees.The intercropping system provides more available water resources for jujube tree transpiration in flat water years and drought years.?5?From the perspective of the model,the influence mechanism of intercropping compound system on jujube tree transpiration water consumption is revealed.The model results showed that,within three years,the fitting results could meet the accuracy requirements of the model.As the year of verification increased,the root mean square error?RMSE?and the consistency coefficient?d?increased and decreased linearly,respectively.Jujube trees in the two intercropping systems showed mild water stress in flat water years,and the jujube trees were still under moderate water stress in the control treatment;in the drought years and the flat water years after the drought years,the jujube trees were severe and moderate in the control treatment.Under the water stress conditions,the intercropping system significantly improved the water stress environment of jujube trees,and increased the transpiration rate and transpiration of jujube trees,which was consistent with the measured results.It is verified that in the intercropping system,the improvement of the water environment of the jujube tree reduces the water stress on the jujube tree and eventually increases the transpiration of the jujube tree.The above research showed that the inter-composite system,as an economically feasible orchard management measure,plays an important role in improving the soil moisture status of jujube trees,increasing the transpiration of jujube trees and improving the physical and chemical properties of the soil in semi-arid rain-fed orchards.Compared with daylily,canola has a higher degree of soil microenvironment improvement,weaker water competition with jujube soil,and significantly reduced the dry layer of the orchard soil.Therefore,in rain-fed orchards in the loess hilly area,jujube/canola intercropping system can maximize the use of water resources?water conservation?and minimize competition?water competition?,which is conducive to achieve the sustainable development goals of jujube orchard.