Simulation Study On The Regulation Effect And Mechanism Of Soil Water And Nutrient Under Jujubes And Living Covers Compounding System

Since the Grain for Green project in1999on the Chinese loess hilly region, theecological restoration and construction have made great achievements. The cultivated area ofthe jujube, which is the local and traditional economic-fruit, gets rapid development. Thedrought and water shortage, as well as the conventional soil management (clean cultivation)in rain-fed jujube orchards cause a series of issuses, such as the orchard soil degradation,relatively low fruit production. Compounding system of fruit tree and living covers has beenthe main soil management in orchards for Europe, UAS, Japan and other developed countries.The relatived study is the hot issuse in the field of the orchard soil management. At the end ofthe20ththe century, China brought the living ground cover mangement into the green fruitproduct system in fruit orchards, and promoted it throughout the country. The relatived studyachived greater progress. However, the research on the soil water and nutrient regulatingeffects, and soil water adaptation under the compounding system are still relatively weak.This paper brought fouth kinds of high-quality pasture on the Chinese loess hilly region intothe production and construction of jujube orchards. By means of the simulated compoundingsystem of jujube and living covers (CSJLC), the effects of the CSJLC on soil physicalproperties, the surface runoff and sediment, as well as the soil moisture and its consumption,as well as soil available nutrients were investigated. There were six treatments in this study,the control─clean cultivation (CC) and five compounding systems, which were strip cock’sfoot (Dactylis glemerata L.) cover+jujube tree (SCF), strip bird’s foot trefoil (Lotuscorniculatus L.) cover+jujube tree (SBF), strip crown vetch cover (Coronilla varia L.)+jujube tree (SCV), strip white clover cover (Trifolium repens L.)+jujube tree (SWC) andwhite clover full cover+jujube tree (WCC), respectively. The family of cock’s foot is thegrass and others are the legume. Three-year experiments obtained the following results:(1) The compounding system of jujube and living covers (CSJLC) obviously andprositively improved soil physical properties. Numbers of3-6cm length fine roots (<0.15mm)per unite soil volume (100cm3) were obviously greater under the CSJLC than under CC. Thecorrelation coefficient between soil proposity, available water content and the fine rootnumber are0.8432(P=0.010) and0.765(P=0.005), respectively. After three years, the soil field capacity, capillary, available water content and saturated hydraulic conductivity underthe CSJLC increased by6-9%、14-21%、13-19%and5-30%, respectively. At high soil suction(>0.25bar) under the CSJLC, the soil water content obviously increased, while the specificwater capacity slightly reduced, both of which indicated that the soil water holding capacityand the soil water supply capacity (drought tolerance levels) strengthened.(2) The CSJLC showed apparently soil and water conservation, and increasedsignificantly vegetation interceptions and soil infiltrated rates. The mean interception underthe CSJLC was5-8mm, which accounted for8-11%of the individual rainfall amount. Bothof them were significantly greater that that under CC (P<0.05). The interception calculationmodel was built as I nt3.168LAI[1(1Rai/125)3.773]based on the rainfall amount andleaf area index data. The CSJLC significantly postponed the time to runoff and decreased thetotal runoff and sediment yield (P<0.05), compared with CC. The runoff depth for strip covers,full covers and CC treatments were8.1-18.0mm,4.4-8.4mm and16.7-59.3mm, accountingfor10.4-28.6%,5.0-18.0%and15.6-74.4%, respectively. The CSJLC significantly increasedsoil initial, mean and stable infiltrated rate (P<0.05). The mean value of the above three itemsunder the CSJLC were around1.3-1.35,1.4-1.8and1.2-1.4times than that under CC. Theinfiltrated ability ranked as WCC>SCF>SBF>SCV>SWC>CC. Under the similar individualrainfall amount, the wetting front migration depth under CSJLC was around60cm, while itjust was45cm under CC.(3) The CSJLC significantly increased soil moisture increment (SMI) after the individualrainfall event. However, the moisture was lower under the legume cover than under CC,because of the living covers consumpting soil water. The SMI under WCC was the largest(58.3±14.3mm), while no difference in SMI was found among all strip covers. The SMI underthe strip cover, full cover and CC treatments accounted for61.2-75.4%,76.4-83.5%and11.4-63.0%of the indvidual rainfall amount, respectively. The SMI for all treatments rankedas WCC>SCF>SCV>SBF>SWC>CC. The soil daily water consumption (SDWC,evapotranspiration) among all treatments reached to a significant level (P<0.05). The SDWCunder WCC was the largest with the mean of5.42±1.6mm day-1, and the rest ranked asSCV>SWC>CC>SBF>SCF. The extra consumption soil water for the living covers causedsoil moisture reduction to some extent. The soil moisture under SCF was the largest. Themoisture was significantly less under the legume covers than under the grass covers (P<0.05).The mositure ranked as SCF>CC>SBF>SWC>WCC>SCV. The soil water consumption wasrelatively high at the blossoming and setting stages, as well as the fruit growth period, whilewas quite small at the fruit maturity stage.(4) Based on the water balance equation, we simulated the soil infiltrated process and surface runoff generation by using the unsaturated soil physical parameters, the revisionaryGreen-Ampt infiltrated model, and the wave equation of movement of the overland flow. Therelative error between the simulated data and true data for around80%infiltrated data and98%runoff data were less than20%, and the Nash-Sutcliffe statistic coefficient betweensimulated and true data were over0.99. Both of them indicated that the simulated results wereideal. The simulated data of the interception, infiltrated water amount and runoff depth underthe CSJLC accounted for10-14%,65-75%and6-18%of the individual rainfall amount,respectively. The rainfall amount distribution proportion (interception:infiltration:runoff:loss)under thre strip cover, full cover and CC treatments were12.1：68.1：16.0：3.9,14.0：75.1：6.4：4.5and6.7：47.1：41.6：4.6, respectively. The CSJLC realized maximumly the rainfallinfiltration on the slope, which is significant for improving rain resources utilization.(5) The water competition event (WCE) between the living covers and jujube tree wasconcentrated from March to July per year, and the cumulative frequency was over70%. Thefrequency of occurrence at July was the largest of36%. The occurred frequency desired valueof WCE was45%,37.5%and30.4%under200mm,300mm and400mm cumlative rainfallamount during the growth stage. Pearson’s correlation coefficient between the occurredfrequency and the rainfall amount and the living cover species was-0.9935(P<0.01) and0.5065(P<0.05). Under this simulated trail condition, the cover strip width should be not over0.54m, and accounted for around22.5%of the line spacing between two jujube trees(calculated on2.0m).(6) There was no significant effect of the CSJLC on soil available nitrogen (AN),available phosphorus (AP), and soil water soluble organic carbon (WSOC), compared withCC. The mean value of AN ranked as SWC>CC>SBF>SCV>SCF>WCC. The AP in year2012was significantly less under the CSJLC than CC (P<0.05), and the mean value ranked asSCV>SWC>CC>SBF>SCF>WCC. No difference in WSOC was found among all treatments(P>0.05), and the mean value ranked as SBF>SCF>SCV>CC>WCC>SWC. The CSJLCsignificantly reduced the AN and AP loss in sediment (P<0.05), compared with CC. The leastdata of the AN and AP loss were obtained under WCC, and they were0.23g for the AN and0.16g for the AP.(7) The jujube tree’s height was significantly greater under SCF than others (P<0.05). Nodifference in the diameter of the jujube tree was existed among all treatments (P>0.05). Thegrowth ratio of height and diameter was slightly greater under the CSJLC than CC. Thebiomass per unit area of the living covers was significantly greater under SCF than others(P<0.05). The leaf area index of jujube trees and the living covers, as well as the SPAD dataof the jujube trees’ leaves showed a rising trend at the growth period, while the SPAD data of the living covers showed a fluctuatedly downward trend at the same period. The CSJLCincreased the net photosynthetic rate and intercellular CO2concentration of the jujube leaves,but the photosynthetic active radiation use efficiency under CC was the largest.(7) Based on the above results, six kinds of experimental items were chose as theassessed criteria: soil moisture, surface runoff reduction, sediment reduction, soil availablenitrogen, available phosphorus and soil water soluble organic carbon. We assessed theeffectiveness of four kinds of strip cover treatments by the analytic hierarchy process and thegray multidimensional comprehensive feudatory degree evaluation. The results indicated thatthe compounding system of the cocks’ foot strip cover+jujube tree is the best technical modeof the CSJLC. This result was exactly same as that of the qualitative analysis results.