| The Jujube cotton intercropping is one of the important types of agroforestry system.It has become one of the effective measures to solve the use contradiction between agriculture and forestry land,improve land use efficiency and increase economic benefits in the early stage of fruit tree establishment.The interspecific competition relationship of agroforestry system is complex,and there are underground competition for water and fertilizer resources and competition for light and heat resources on the ground Studies on interspecific competition among drip irrigation intercropping systems in arid areas are rarely reported.In this paper,the jujube cotton intercropping system in the northwestern margin of Tarim Basin is taken as the research object.Through field experiment,the evapotranspiration law of the intercropping system was studied by means of large scale lysimeter,and the root distribution characteristics of the intercropping system were analyzed by mining method combined with the DT-SCAN root analysis system Furthermore,the niche competition theory was used to define the underground competition.The purpose of this study is to provide theoretical support for the system of planting structure,optimization of irrigation system and field management.The main research conclusions are as follows(1)In monoculture and jujube cotton intercropping systems,all the changes of soil water content showed a downward trend over time during the whole growth period.In the vertical direction,the variation coefficients of soil moisture showed a decreasing trend with the increase of soil depth,and it was the largest in the surface layer(0-20cm).The variation coefficients of soil moisture under intercropping mode were significantly lower than those under single cropping mode.This indicates that the soil moisture stability of the intercropping system is higher than that of the monoculture system due to the obvious effect of the surface covering.In the horizontal direction,the farther away from the trunk,the lower the soil moisture content of the Jujube monoculture system will be in the root zone.In the range of 75 cm away from the trunk,the soil moisture descended slowly,and decreased significantly within 75 cm-175cm from the trunk.The distribution distance of drip irrigation zone plays a decisive role in soil moisture distribution In the jujube-cotton intercropping system,the average soil moisture content in the range of 75 cm from the trunk was higher than 6%of that in the range of 75cm away from the trunk due to the irrigation.(2)The peak value of evapotranspiration(4.42mm/d)of JuJube monoculture System appeared at flowering stage,while the peak value of intercropping system(6.79mm/d)appeared in young fruit stage.The peak value of evapotranspiration in intercropping system is 53.6%higher than that in single cropping system,and the giowth period appears to be later than that in single cropping system.Compared with the ETo results calculated by FA056-PM and ASCE-PM model under the hourly and daily steps in the arid area of Northwest China,the predicted ET0(Reference Crop Evapotranspiration)value by the ASCE-PM is closer to the measured value of lysimeter,and is more suitable for ET0 calculation in arid area.When the solar radiation value cannot be directly obtained,the daily ETo based on the sunshine hours was calculated by the Angstrom formula,which would lead to the maximum error.The regression constants as and BS in the Angstrom formula can be modified to improve the calculation accuracy.When the average daily sunshine hours are greater than 9h(May-August),the correction values of as and bs are 0.21 and 0.36 respectively,less than 9h(November-October),the as and bs correction values are 0.13 and 0.60 respectively.The parameters can be applied to the 45 degree north arid and semi-arid inland area,and have certain application value for accurate calculation of ET0.(3)The daily variation of net photosynthetic rate(Pn)of all the jujube trees showed obvious double-peak curve during the flowering period and the fruit expansion period,and the peak occurred at 14:00 and 18:00 while the trough appeared at 16:00,that is,"noon break".The Pn value of Jujube tree monoculture was higher than that of jujube cotton intercropping in the growth period of 17.69%.When jujube was in deficit irrigation under intercropping treatment,the Pn of jujube trees decreased significantly during flowering and fruit enlargement,and photosynthetic rate was inhibited.Cotton deficit irrigation has the most obvious effect on cotton photosynthesis.The physiological indexes such as Pn,Tr(transpiration rate),WUE(water use efficiency)of jujube trees increased significantly with the growth of tree age,especially for Jujube tree monoculture system.(4)The indexes of underground biomass of Jujube tree monoculture were better than those of jujube cotton intercropping.In 2014,2015 and 2016,the root length of jujube tree was 47.96%,9.65%and 40.53%higher than that of intercropping.In the Jujube tree monoculture treatments,the root length of the jujube tree during the growth period was 3.34 times and 1.16 times that of the flowering and fruit development stages respectively.The root weight of the fruit development period was 21.87 times and 7.28 times that of the flowering and young fruit stages respectively,and root diameter was 2.3 1 times and 1.32 times respectively.The root biomass increased with the increase of tree age,and it increased by 283%and 194%in 2016 compared with 2014 and 2015 respectively.In the Jujube cotton intercropping treatments,the roots of jujube trees under young fruit period entered the vegetative growth stage,and the number of absorbed roots increased significantly.In the fruit development stage,the root weight of jujube tree increased significantly 19.26 times and 4.59 times that of flowering stage and young fruit stage,and the root diameter increased by 1.73 times and 1.26 times respectively.The root gathering area had a downward trend.The annual root growth of jujube tree increased with the increase of tree age,and the root length increased by 151%,136%and 146%respectively in 2016 compared with 2015.The root distribution extended from horizontal 0-40cm to 0-80cm,and the vertical depth extended from 50cm to 60cm.(5)For the treatments of intercropping system,the roots of jujube tree showed a trend of growing towards cotton in different growth stages.In the horizontal direction within 20 cm-60 cm from the trunk,the root overlap degree of jujube cotton intercropping system was high,and the competition for water was the most intense.The horizontal distribution of the roots of jujube tree spread from 0-40 cm in 2014 to 0-80 cm in 2016,and the root length of overlapping area proportion of total root length increased from 39.9]%to 65.12%.horizontal competitiveness index of full irrigated jujube trees were greater than cotton during the growth stage and there were no significant difference(P>0.05).Horizontal competitiveness index of deficit irrigation jujube was significantly greater than cotton(P<0.05).It indicated that deficit irrigation signifi cantly increased the moisture competition ability of jujube,and deficit irrigation of cotton had less effect to interspecific competition.The competitive ability of jujube trees in the horizontal direction increased with the increase of tree age.In the vertical direction,the competitiveness index of jujube and cotton varied at different growth stages during the year:Competitiveness index of jujube tree has a trend of increasing first and then decreasing with the process of growth stage,and that of cotton has a trend of increasing with the process of growth stage.In different year(2014-2016),the competitiveness of jujube trees was always weak,but the difference was not significant.(P>0.05). |
