Water Budget Of Apple Forest On The Gully Region Of Loess Plateau

Water is the limiting ecological factor which can restrict plant growth, while annualprecipitation is rare and mal-distributed in space and time is the climate feature of LoessPlateau. To research the characteristics of apple trees canopy interception, stem sap flow andits water consumption through transpiration, the changes of soil moisture and evaluate thewater budget status of apple orchard, we conducted a study on the Changwu tableland whichwas typical representative of the gully region of Loess Plateau. The results showed that:1) The characteristics of precipitation redistribution of2011and2012by the apple forestcanopy was as follows: the throughfall rate of young apple forest (YAF) greater than elderapple forest (EAF), the stemflow rate of YAF greater than EAF and20122011, theinterception rate of EAF greater than YAF and20112012. The throughfall rate, stemflowrate and interception rate were greatly impacted by rainfall and canopy density. Throughfall,stemflow and canopy interception accounted for90%～93%,1%～3%, and5%～9%of thetotal rainfall, respectively. The relationship between throughfall and total rainfall was theparabolic curve opening upward. The relationship between stemflow and total rainfall can beexpressed by a linear equation approximately. The relationship between canopy interceptionand total rainfall was expressed by the cubic polynomial. The total interception loss (28.46mm) which was estimated by the Gash model was less than the measured value (30.5mm)6.7%. Compared with other studies, the good agreement between the estimated and measuredvalues indicated that Gash analytical model was suitable for estimating canopy interceptionlosses on the Loess Plateau.2) The diurnal variation of sap flow displayed unimodal curves, and it had the obviouscircadian regularity. The velocity of sap flow was as follows: sunny day> cloudy day> rainyday; day> night; young tree> elder tree. There was no significant difference at starting time,peak time, dropping time of sap flow between EAF and YAF in different weathers respectively.The EAF and YAF average monthly stand transpiration was66.5mm and30.0mm,accounting for65%,30%of the average monthly rainfall respectively. The EAF and YAFtranspiration showed a trend of gradual decline from July to September. Sap flow velocity was significantly correlated to total radiation (Eg) and air temperature (Ta), and was negativelycorrelated to relative humidity (RH). The ranking of correlation coefficients was Eg> Ta> RH.The regression model was very significant by analysis of variance test, and can be used topredict the sap flow velocity.3) The soil water content of apple orchard had obvious seasonal variation. Young appleorchard (YAO) exceeded elder apple orchard (EAO) in soil water content (SWC), but both ofthem had the basic consistently variation tendency: the SWC unchanged before April, declinedfrom mid-April to the end of August, and increased after September. The soil water storagecapacity (SWS) of YAO was greater than EAO. From the end of September2011to the end ofSeptember2012, the SWS of EAO and YAO dropped, the SWS consumption: YAO EAO.The water use depth of EAO and YAO was about240cm and540cm. The SWC of EAOgenerally presented a declining trend in0~600cm on the profile, but the YAO showed a trendof increase. Using standard deviation and coefficient of variation of the soil moisture contentto classify the vertical layer, the results showed that: the rapid change layer was above10cm,the active layer was from10cm to80cm, the relatively stable layer was below80cm.4) Soil evaporation depended on the SWC firstly then by meteorological condition. Themaximum evaporation attained4.0mm/d at ideal conditions. The average daily evaporationwas close to the forest stand transpiration level at the same period. The average dailyevaporation and monthly amount of evaporation as follows: July May August JuneSeptember. During May to September, the total rainfall was402.4mm, the total evaporationof EAF and YAF was178.4mm,215.8mm, accounting for44%,54%of the total rainfall. Thesoil evaporation of YAF was greater than EAF all along.5) During July to September, the rainfall was305.2mm, the transpiration, soilevaporation, canopy interception of EAF and YAF was199.6mm and90.2mm,110.7mm and135.9mm,20.8mm and10.8mm respectively, transpiration soil evaporation canopyinterception. The change of SWS which was estimated by water balance equation did notmatch with the measured values. The amount of water use was in a state of imbalance bothEAF and YAF within the scope of600cm.