Study On Spatial Distribution Characteristic Of Deep Fine Root And Soil Water On Jujube Plantation In Loess Hilly Region

Soil water absorbed by deep fine root play an important role in forest land waterconsumption, maintaining forest evapotranspiration, and growing in arid and semiarid region.Oriented at commonly occurred soil dry layer problem in artificial economic forest in loesshilly region, this paper aimed at dwarfed drip irrigated densely jujube plantation primarily,widely jujube plantation without irrigation as control, stuied deep root distribution and soilwater profile dynamics. It would have important significance in artificial economic forestwater management and sustainable development. A soil coring method with a LuoYangshovel was used to obtain root sampling from surface to maximum fine root depth until nomore roots in consecutive two soil layers. Through indoor processing and data analysis, fineroot spatial distribution, deep soil water stratifying characteristic based on root distribution,the effect of stand age and drip irrigation on jujube plantation fine root distribution and soilwater were investigated. The main conclusions of this study were as follows:（1） Fine root dry weight density （diameter<2mm） decreased with soil depth andincreased with stand age. Horizontally, fine root dry weight density was larger in the nearestof the trunk than other position in2and4-yr-old jujube plantation, while it was higher in thenearest of the trunk and the centre of the four trees in9and12-yr-old jujube plantation, and ithad no significant difference among different horizontal position in the same year old jujubeplantation. Vertically, the relation between fine root dry weight density and soil depthconformed to power function,63%of fine roots concentrated in0-0.6m soil layer. Sequentialcluster stratifying results highlighted the fine root vertical distribution characteristic. Fineroots were divided into three layers, i.e. dense root layer （0-0.6m）, diffusion root layer（0.6-1.6m） and sparse root layer （1.6-5m）. The fine root dry weight density was619.1,1109.84，1360.14，2319.41g.m^-3in2,4,9and12-yr-old jujube plantations respectively. Thetotal fine root dry weight had significant difference among different jujube stands.（2） It showed that the maximum fine rooting depth increased with stand age andmaintained stable after9years. The maximum fine rooting depth reached2m in2-yr-old jujube plantation, it extended4m in4-yr-old jujube plantation, it reached5m in a9-year-oldjujube plantation, but it stabilized and did not increase thereafter. And it was5m in9-yr-oldand12-yr-old jujube plantation respectively. The maximum fine root depth extended deepinto the soil rapidly during the first four years, but more slowly in the subsequent five years.The cumulative percent of fine root dry weight density D50was always located in0-0.8m soillayer, but D95extended deeper into soil with stand age.（3） Combined with root distribution characteristic, the stratification result of soil watercould well reflect jujube plantation soil water depletion status. Deep soil water （below2m）was divided into three layers, i.e. strong depletion layer （2-4.4m）, less strong layer （4.4-5m）and weak depletion layer （5-7m）. Root extended deep to absorb soil water gradually withstand age, thus soil water was depleted until wilting point, formed a low soil water zone, andthe low soil water zone was located in the maximum precipitation infiltration depth and themaximum fine root depth. Soil water content decreased gradually between2^-3.6m, and itwas higher than wilting point in4-yr-old jujube plantation. The low soil water zone wasoccurred in1.8^-3.6m both in9-yr-old and12-yr-old jujube plantation, and the soil water wasclose to wilting point. It showed that4-yr-old jujube plantation has depleted deep soil waterslightly, fine root has depleted deep soil water completely after9years, and thus there wasserious dried layer in this soil layer. The relationship between fine root dry density and deepsoil water content was negative.（4） Irrigation has significant effect on fine root dry weight density, the maximum fineroot depth and soil water content. Fine root dry weight density was higher in densely jujubeplantation than widely plantation, and the total fine root dry weight density was2319.38g.m^-3in densely jujube plantation, while it was1969.06g.m^-3in widely jujube plantationrespectively. The maximum fine root depth in densely jujube plantation was only half of thewidely jujube plantation, it extended5m and10m respectively. The profile soil watercontent was higher in densely jujube plantation than widely jujube plantation in0-10m soildepth. It was8.52%and6.6%respectively. The low soil water content zone moved up indensely jujube plantation, it located in1.8^-3.6m in densely jujube plantation and1.8-4.6m inwidely jujube plantation. Irrigation water equivalent to7.4%average rainfall had animportant effect on the maximum rooting depth. Jujube could reasonably adjust root depthaccording to the surface soil water supply status. Although dried layer has occurred in jujubeplantation, drip irrigation could reduce the maximum fine root depth, alleviate deep soil waterconsumption, and inhibit the dried soil layer formation, a certain amount of irrigation couldmaintain the forest land sustainable development.This conclusion has important significance in jujube water management and vegetation restoration. It can provide theoretical basis for revealing the process of deep soil waterconsumption in artificial economic forest.