| Soil water balance method, Sap flow method, and microclimate monitor system wereemployed in this study to investigate water budget at the different spatial and temporal scales.The study site is located in Changwu tableland which is typical representative of the gullyregion of Loess Plateau. On the basis of fixed-point monitoring, we analysed thecharacteristics of apple trees canopy interception, soil evaporation, stem sap flow and itswater consumption through transpiration, the changes of soil moisture, and evaluated thewater budget status of apple orchard. The main results were as follows:Forest canopy is one of the important factors affecting atmospheric rainfall redistribution,which it changed the hydrological cycle. Rainfall level had an impact on precipitationredistribution. With the increase of rainfall level, the throughfall, the throughfall rate, thestemflow, the stemflow rate and the interception all showed a trend of increase, but theinterception rate decreased. Compared with the7age orchard, the17age orchard had lowerpenetration rate and higher entrapment rate. The throughfall dominated in the process ofprecipitation redistribution. Linear regression model best reflected the relationship betweenthroughfall and total rainfall as well as the inverse functional correlation between throughfallrate and rainfall. Stemflow accounted for the proportion of total rainfall is very small, andwhen the rainfall was less than1mm, there were no stemflow. When rainfall was more than1mm, stemflow began to appear. Then, the stemflow linearly increases with the increase ofrainfall, while the stemflow rate increased along with the increase of rainfall in a logarithmicgrowth trend. When rainfall was less than1mm, almost all precipitation was intercepted bycanopy. It had obvious linear function relation between Interception and precipitation, whileinverse function relation between interception rate and precipitation. Three characteristicparameters (precipitation, rainfall duration, rainfall intensity) and three meteorological factors(temperature, relative humidity, average wind speed) were chosen to be analyzed thecorrelations with the throughfall, stemflow and interception. Results show that they were allsignificantly correlated with precipitation, and mean rainfall duration, average rainfallintensity.Soil evaporation is an important component of the evapotranspiration. Micro-lysimeter was used to continuously measure the soil evaporation of orchards in Changwu County inLoess tableland area of China. The purpose is to ascertain the soil evaporation process ofdynamic change after the rain and the relationships between the soil evaporation andmeteorological factors and water surface evaporation. The results showed that the curve ofdaily soil evaporation was pulse shape, and the soil evaporation of7age orchard was slightlymore than the age of17-orchard. Soil evaporation was closely related to whether there wasrain in the previous day. The soil evaporation process could be divided into three stages,namely evaporation-speed-stage, fluctuating stage and stabilization stage. Solar radiation andvapor pressure deficit (VPD) were the main factors. Soil evaporation was significantlycorrelated with water surface evaporation.Transpiration is an important part of the evapotranspiration process, and a majormechanism of the water cycle and balance in the atmosphere. But there were few reportsabout the water consumption of economic forests related to sap flow rate, especially for appletrees in the Loess Tableland. In this study, a thermal dissipation probe (TDP) was used tocontinuously measure the sap-flow rate of apple tree in Changwu County in Loess tablelandarea of China from July to October,2012. The purpose is to ascertain the characteristics ofwater consumption of apple trees and the relationship between the sap-flow rate andmeteorological factors. The results showed that diurnal variation of the sap-flow rate of appletree was a single peak curve in both sunny and rainy days. On sunny day, the sap-flow startedmore early and stopped more lately than on rainy day. The sap-flow rate of apple tree waspositively correlated with solar radiation, vapor pressure deficit (VPD), wind speed with alinear equation, and negatively correlated with air relative humidity. The dependency ofsap-flow rate on various meteorological factors on the sunny day was more significant thanon the rainy day. In addition, the sap-flow rate of apple tree varies distinctly in differentenvironment conditions of soil moisture. Under the water stress condition, the sap-flow ratewas significantly lower than that under the moist soil condition. The change of sap-flow rateshowed a broad-peak curve, indicating that the transpiration was higher under the moist soilcondition. Our study may provide local farmers and forest managers with valuableinformation about the transpiration and water consumption of apple trees in the study area,which is conductive to the scientific management of local economic forest ecosystem.Soil moisture is an important impact factor of agricultural production and regionalecosystem. The Loess Tableland was selected as the study area, and the characteristics of thedynamic of soil moisture in different orchards were analyzed in this article. The resultsshowed that: the soil moisture of7-year apple orchard was more than the17-year appleorchard. The variation trends of soil moisture content of different land use types were as same as the variation trend of precipitation in the observation period, but its change lagged thechange of precipitation. Variation range of soil moisture content reduced with increased soildepth in different orchards; in addition, there was also a seasonal diversity in the watercontent change of soil profile in every land use type. There were no soil desiccation occurredin7-year apple orchard, while relatively deep desiccated soil layers existed in17-year appleorchard and the distribution depth was about320~600cm. There were some differencesbetween the soil moisture depletion and infiltration depths of different land use types. Thedepth of soil water depletion of17-year apple orchard was500cm, while the waterinfiltration depth was over the200cm. The depth of soil water depletion of7-year appleorchard was200cm and infiltration depth was over the determination of soil depth.Water balance is one of the important indicators of ecosystem function and feature.Generally, the soil water cycling of orchards were in a state of balance, but the evaporationwas slightly greater than precipitation. In the long term it will cause serious deficit of soilmoisture, and eventually led to the formation of soil dry layer. Throughout the period ofobservation, the soil evaporation is big in the early stage, and had a tendency to decreasegradually. The ratio of soil evaporation of evapotranspiration were52.0%and44.4%respectively in7and17age orchard, indicating non-production water accounted for asignificant proportion in the whole period of growth. This study did not consider the surfacerunoff when using the water balance equation, but actually it would cause surface runoff inthe heavy rain, and it had a significant effect on water balance. So it was recommended thattaking the error caused by the rainstom into consideration when using the water balanceequation in the region. |
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