Soil Water Use And Competition In Jujube-crop Systems On The Hilly Region Of The Loess Plateau

Since the implementation "Grain for Green" of the Loess Plateau.Jujube as a traditional drought-resistant species,make a significant contribution in local ecological restoration and to bring economic income for residents.Traditional management in jujube orchard is the clean tillage,which aims to reduce weeds and jujube seedling competition for water and fat in soils.The result of long-term clean tillage in jujube orchard sloping farmland soil moisture evaporation invalid,loose soil and nutrient loss,etc.Practice has proved that agroforestry plays an important role in the loess plateau soil and water loss,restore ecological balance and improve the efficiency of land use efficiency.But the loess hilly-gully region is located in the semi-arid areas where rainfall resources are limited,groundwater buried depth which cause the unsaturated zone soil water can not be replenished effectively,therefore agroforestry system mode may lead to a serious water competition because of the increase of biomass.The soil water use strategy of plants is an important method to determine whether there is a competition about soil moisture.The stable isotope tracer technique is an effective method of plant water use strategy: By contrast the isotopic composition of plant xylem water and soil water of different depth can determine the different soil layer water use ratio.In this way can we analyse the moisture competition between two kinds of agroforestry systems.In this study,we introduced to cash crops,Feed Brassica napus and Hemerocallis fulva intercropping between rows in jujube orchard.The primary objective of this study was to investigate plant water use strategy at different growth stages by using stable oxygen isotope(18O)and Isosource model in the jujube-crop agroforestry systems to evaluate their feasibility in this region.Here three potential water sources were identified: shallow(0-20 cm),middle(20-60 cm)and deep soil water(60-120 cm).In this experiment we obtained the following results:The rainfall distribution in the study area is not balance,spring is the critical period of jujube water demand,there need appropriate filling water.The rain capacity increase in summer and autumn,agroforestry can increase the Interception amount of surface runoff to recharge the soil water content.The main factors influencing the isotopic composition of rainfall in the region is air temperature not rainfall unless the rainfall intensity reached a certa in degree.All stable isotopes of soil water fall to the right side of the fitting line of precipitation,reflecting the strong evaporation effect on soil water.The most stable isotopes of stem water fall around the fitting line of soil water,indicating stem water of crops originating from soil water.And a small amount fall close to the fitting line of precipitation,indicating there is some other water source.The soil water content change drastically in this area in the region of 0-20 cm,is not conducive to plant uptake.Heavy rain in 3 to 5 days can infiltration to the 60 cm of crop root dense layer,which is easy to be absorbed,however the soil moisture below 60 cm is hard to get the timely and effective supplement.Single from the perspective of soil water supply,jujube-Feed Brassica napus intercropping system is more suitable for the local climate than jujube-Hemerocallis fulva intercropping system,because their water use time is dislocation.In the drought period of may and July Jujube main use the middle and deep soil water,and main use the middle soil water in August and September when Rainfall increase,but use less shallow soil water in the whole growth period.Feed Brassica napus and Hemerocallis fulva main absorption middle soil water during the dry period,but the surface root of Hemerocallis fulva responsive of effective rainfall sensitive ly.Both Feed Brassica napus and Hemerocallis fulva use more shallow soil water in the Rainy Season.The water use strategy of Jujube 、 Feed Brassica napus and Hemerocallis fulva exists obvious difference,but there exists a certain extent in May and July about middle and deep water.