| It has become an international topic how to improve the utilization of rainfall and limited water resource,to reduce the water requirement and consumption by agriculture.Soil moisture plays a very important role in crop growth,vegetation recovery and ecological construction.Recently,with the application of new technologies and method,such as geo-statistical technologies and fractal theory,wavelet analysis in China have made great achievements in the fields of modeling water transport in agro-ecosystem,temporal and spatial variation,optimizing and regulating field water in agriculture and so on.However,most of current the researcher focus on north China plain and the loess plateau,the semiarid zone of China.And do apoor job in hills and mountain area,especially the study of the areas of southern China with seasonal drought in Chongqing.Topographic attributes are also useful indicators of hillslope and mountain hydrological dynamics.Hillslope hydrology remains challenging because a number of processes interact at different scales,significantly contributing to the complexity of the systems that hampers the possibility theory.Hills and mountain area was in an absolute dominance with the proportion of 90%of study are in Chongqing.Besides the complicated topography,the slope cultivated land which slope is more than 15°is about 50%proportion of cultivated land area.And in this region soil erosion and water shortage is serious and seriously limits the sustainable development of agriculture.In this research,a typical hill and mountain area of Chongqing in China is selected as an experiment area,where the soil is used to analyze the soil moisture dynamics and their environmental factors.The research provides a scientific basis for demonstrating and spreading of anti-drought technologies and soil moisture utilizes efficiently.This study focused on providing scientific basis for solving the season drought problem in hill and mountain area in Chongqing.According to the spatio-temporal variation of soil moisture in research region, 90 soil sample was sampled in different county in Chongqing and soil OM.soil particle distribution,soil water retention curve,soil diffusivity was measured,and utilized these data to select out a best point and parameter PTFs model to predict soil hydraulic parameters in Chongqing,and then collected 160 soil profile data,such as soil bulk density,soil particle distribution and soil OM to estimate soil field water capacity,wilt point and hydraulic parameter in research region,based on these estimation,Spatial variation of soil hydraulic parameters was analyzed.Spatial characteristics of unsaturated soil water movement parameter are the base and precondition of scientific understanding soil moisture dynamistic variation of large-scale.In order to further study on temporal and spatial variation of soil moisture in hilly and mountain in Chongqing,54756 data for soil moisture in 84 times were collected from March to September in 2006 and 2007.The soil moisture in layers of 0-10cm,10-20cm,20-40cm was measured at an interval of 5 days. All the data were analyzed by methods of the traditional statistics,geo-statistics,rank stability and wavelet analysis to investigate the spatial-temporal variation of soil moisture.The water holding capacity of soil, precipitation transport on sloping land,soil moisture dynamics and its affecting factor had been discussed in this paper.The main achievements of this study are as follows:(1)There is a big difference for soil water capacity,when the soil texture is coarse,soil reduces water discharge quickly,and soil texture is heavy,a narrow range of the available soil moistureThe specific water capacity decreases to the scale of 10-2from 10-1,and to the scale of 10-3from 10-2 when the water potential decreases from-0.l0～1×105Pat o-l×105Pa～-5×l05Pa,and then to-5×105Pa～-10×105Pa The soil water content decreases very slowly and the soil water discharge rapidly with a small amount when the suction exceeds 5.0×105kPa..This is the reason that soil is frequently influenced by seasonal droughts.The relationship between soil moisture diffusivity and soil water content in every soil layer were sharp positive exponential function as well as between soil moisture conductivity and soil water content,and these relationship were significant by statistical analysis.The van Genuchten(l=0.5,m=1-1/n)hydraulic parameters was fitted to soil water retention and soil diffusivity,the results are as follows,when soil texture is coarser,the value ofθr andθs is lower,but the value of a,n is higher.So the available soil water which soil is heavy texture is lower than which in median texture,the hydraulic parameters Ks cannot be used as a matching point for the hydraulic parameter in field or laboratory experiments.Then,the bulk density,porosity,the type of pore,particle constitute and organic carbon in the soil affected the soil moisture diffusivity.The water-holding capacity of soil is negatively related to contents of sand fractions with the size from 2mm to 0.05mm,there is a significant positive correlation between clay content and soil water under different tension,soil organic matter and soil water under＜0.33×105Pa,there is no significant positive correlation between bulk density,porosity and soil water under different tension. Sandy particle and clay particle is the important factors influenced soil water capacity.(2)Pedotransfer function of EPIC and RETC model is the best model to predict soil hydraulic parameters,based on these research,the spatial variation of soil hydraulic parameters occurs scale effect. Temporal and spatial variation of soil moisture is the based on the spatial variation of soil hydraulic parameters.Thirteen pedotransfer functions(PTFs),namely RERC,Brakensiek.Rawls,British Soil Survey Topsoil,British Soil Survey Subsoil,Mayr-Jarvis,Campbell,EPIC,Manrique,Baumer, Rawls-Brakensiek,Vereecken,and Huston were evaluated for accuracy in predicting the soil moisture contents at field capacity(FC) and wilting point(WP) of hills and mountain chongqing in china.PTFs were evaluated on the basis of SB,RMSE,EF,MBE,FB,MAE and 1:1 line in software of Irene.The result shows that in the case of the hills and mountain of Chongqing city.the EPIC and RETC were found to be the best methods more than the others.The hydraulic parameters are evaluated using PTF,based on these study,Spatial variation was analysized using Geo-statistics,the results showed that linear variogram model was fitted toθr in 0-20cm when the adjusted coefficient of determination of is 0.7;Accordingly,the nugget is 0.41 and 0.87 in 0-20cm and in 20-40cm respectively;based on these results,spherical and exponential were used to fit toθr.the parameters are all positive and the coefficient of determination was more than 0.87, this implies that spatial variance ofθr operate at multiple spatial scales.Linear variogram models are fitted to the hydraulic parametersθs in 0-20cm,the whole spatial variation ofθs in 20-40cmdon not reach stable state,but the local variation is stable,linear model are fitted to the local stability,and the coefficients of determination is 0.77.and it validates the accuracy of the linear model to fit the local stability.The nugget ofθs are 0.34 and 0.71 in 0-20cm and 20-40cm respectively,that is all different from 0,spatial variation occurred at smaller scale less than the sample length.The change of semivarigram ofαis as well as a stage change,the linear model is fitted to the change.the nugget of model close to 0.there occurred a slight spatial variation in smaller than the sample scale;αand lnαin 20-40cm varies with lag length change and the curve is significantly concavo,thus there occurs no spatial structure.The hydraulic parameters of n and ln(n) had no evident spatial structure in all layers,but ln(n) in 20-40cm is stable in local range,the spherical variogram models are fitted to the spatial variation.(3) There are median variations degrees within seasonal,vertical and spatial distribution of soil moisture,but still contribute to stable temporal series.When a field or a small watershed is repeatedly surveyed for soil water content,locations can often be identified where soil water contents are either consistently larger or consistently less than the study area average.This phenomenon has been called temporal stability,time stability,temporal persistence,or rank stability in spatial patterns of soil water contents.Temporal stability is of considerable interest in terms of facilitating upscaling of observed soil water contents to obtain average values across the observation area, improving soil water monitoring strategies,and correcting the monitoring results for missing data.The objective of this work was to contribute to the existing knowledge based on temporal stability in soil water patterns using frequent multi-depth measured with micro-wave oven。Water contents at 0-10cm,10-20cm,20-40cm depths were measured every 5 days for 7 months of observation from March to September in 2006 and 2007.Temporal stability are analyzed using temporal stability index suggested by Pachepsky, The temporal stability index ranges from 0.22-0.34 and decreases with depths,the temporal stability increase with depth.The statistical hypothesis could not be rejected that data collected each five days,each ten days,each fifteen days had the same temporal stability.The spearman correlation parameters aim to describe the temporal variation of temporal persistence.The coefficient of correlation from March to May is higher than the value from June to September.The locations of which were best for estimating the average water contents were different for different depths.The best three locations for the whole observation period were the same as the best locations for a month of observation in about 60%of the case. Temporal stability for a specific location and depth could serve as a good predictor of the utility of this location for estimating the area-average soil water content for that depth.Temporal stability could be efficiently used to correct area-average water contents for missing data.Soil water contents can be upscaled and efficiently monitored using the temporal stability of soil water content patterns.The study of the temporal and spatial dynamics of Soil moisture is critical to understanding of several ecological hydrological processes,e.g.,water stress to plant,hydraulic control of soil nutrient cycle,plant water competition,and also is focus of ecological hydrology.Based on the data of every five days for soil moisture from 2006Y to 2007Y at mountain Mudong sites in Chongqing where soil moisture can be serve as a good predictor of the utility of this location for representing the area-average soil water content for the whole Chongqing,the dynamics of soil moisture were analyzed.The results showed soil moisture values observed at all depths are higher in rainy year than in dry year,in contrast to this,the variance is lower in dry year than in rainy year under subtropical climate.The seasonal dynamics of soil moisture can be divided into two stages:less unstable stage(from Mar to May),and unstable stage(from June to Sept).Soil moisture stochastic dynamics at a point is studied in detail utilizing the probability distributions.The peak value of soil moisture lied in about〈s〉=80%in 06 year,while in 07 year,the peak value lies in about〈s〉=90%。Soil water peak increases with soil depth in different years.Soil water do not increase with depth is increasing completely and the profile distribution can be devided into four structure(soil is stable with depth,increase with depth,fluctuate with depth,decrease with depth)in different temporal scales.By using standard deviation and variation coefficient,the vertical layers of soil water content can be divided into two layers,active layer(0-l0cm)and sub-active layer(10-40cm).There are similar saltation point distribution and periodic span between the adjacent layers. There are the most salsation points in 0-10cm,the mutual spectral of coefficient in different layer closes to 1,that implies that the mutual relationships are evident in soil vertical transmission.Variation coefficient of soil moisture range from 15.42%to 23.15%,the degree of variation is medium.From the C0/C+C0 comparable values of soil three layers,the value is about 50%,spatial autocorrelation account for the 50% of the level of system variation.Spatial distribution is interpolated using ordinary kriging,to some extent; spatial distribution exhibit similar distribution according to seasonal division and agree with temporal stability of soil moisture dynamics.Mean error predicted with regression kriging by using terrain as ancillary variable reduced respectively by 0.34%,24.29%and 17.71%in 0-10cm 10-20cm and 20-40cm compared to spatial distribution with ordinary kriging.Root mean error reduced by 0.51%,11.35%,11.40% respectively,the spatial distribution of soil moisture which predicted with regression kriging varies typically with the terrain characters.Temporal and spatial of soil moisture closely related to soil water storage.Spatial correlations are analyzed with geo-statistics.In research site,the variance coefficient of transmission volumetric capacity outperformed 70%,degree of variance is very strong,while variance coefficient of total soil reservoir capacities,available soil reservoir and unavailable soil reservoir range from 10%to 50%,degree of variance is medium.Spatial semivarigram structures of soil water are anisotropy,spherical and exponential variance model are fitted to soil water reservoir.Spatial autocorrelations account for 61.88%of total variance of unavailable soil reservoir,while the residuals spatial autocorrelations accounts for 75%of total spatial variance,there is a very strong spatial autocorrelations.Soil water reservoir exhibited spotted spatial distribution by interpolating with ordinary kriging in Chongqing.(4)The performance of soil moisture prediction using multiple-linear model exhibits more suitable in cropping growth than in drought period.Three spatial-temporal prediction model was established respectively by using stepwise regression of multi linear model in 0-10cm,10-20cm and 20-40cm,and the model included 6 or 9 index which refer to meteorological factors,terrain factor,soil attributes and land use type.In which the intercept of model in 0-10cm and 10-20cm almost equals to mean soil moisture,while the intercept in 20-40cm is only 3.48 and is far lower than mean soil water accordingly soil layer.Regression coefficient of model combined with specialist's knowledge may analyze the relationship between the independent variable and target variables. The adjusted value of model is more than 0.5 and showed that factors of model can explain less than 50% the change of soil water.F value is significantly(P＜0.01)different.And residuals are normal distribution, and the error value ranges from-2 to 2.This showed the model established can be exploited to simulate spatial and temporal of soil moisture.In order to evaluate the performance of model in detail.the performance of model was analyzed in terms of fitness,Optimum,absolute bias and stability based on the 11 performance indices from March to September,while the model are more optimum and stabile from March to May,but the value is higher in June.August,September as well as the MAE in August,September. Therefore,the performance of model prediction is poor in soil moisture actively fluctuant state.In summary,it can be seen from all above that the soil in mountain has a bigger variance,which leads to which water-holding capacity is variable,a limited specific water capacity,an extremely narrow range of available soil moisture,a thinner soil depth,a poor capacity of anti-drought and a limitation of available soil water in top soil.It is the basic reason that the soil in hills and mountains area of Chongqing is easily to be attacked by seasonal drought and localized drought.Spatial and temporal variation of soil moisture occurs temporal stability in a larger study region,The temporal span of soil water can be devided into two periods according the variability of soil moisture and effect factors:crop growth from March to May. because soil depletion is affected by crop consumption,spatial distribution is similar.Soil moisture changes,the reason are follows as:it was affected by high temperature,serious drought and terrain attributes,even soil moisture increasing with the hight of elevation is increase,thus land use type, seasonal distribution of precipitation and mountain topography which lead to seasonal and regional drought in research region.Based on these researches,soil moisture dynamics was nominated using muti-regression model,Due to a short monitoring span,there occurs obviously seasonal limitation of soil moisture simulation and the accuracy of simulation is lower in drought season than in cropping season. Therefore,it is necessary to take an action to start the engineering construction for available rainfall collection and extend the drying farming technologies combined with agricultural,biological measure as well as the measure for soil and water conversation as to maximize the utilization of rainfall and optimize the effect of soil reservoir on the field water supply.Besides these,In order to solve seasonal and localized drought,it is important to strengthen the dynamical monitoring in regional scale,and applied scientific management technology to forecasting soil drought.
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