Spatio-temporal Variation Of Soil Moisture In Sloping Land Of Guizhou Yellow Soil

Recently,with the application of new technologies and methods,researchers in north China plain and the loess plateau,the semiarid zone of China have made great achievements in the fields of modeling water transport in agro-ecosystem,optimizing and regulating field water in agriculture and so on.However,there are a few researches about seasonal drought in the areas of southern China,especially in yellow soil of mountainous areas,which could not supply enough academic support for the sustaining development of Guizhou agriculture.Nowadays,it has become a key way to solve the problem of seasonal drought for Guizhou how to improve the utilization of rainfall and limited water resources,to reduce the water requirement and consumption by agriculture.The paper focused on providing scientific basis for solving the seasonal drought problem in yellow soil of Guizhou.According to the planting patterns of the crops in yellow soil,three patterns of land utilization were considered involving corn-wheat intercropping pattern,vegetable-vegetable successive cropping pattern and bared land(check) on three slopes of 6.5°,9.5°and 16°in the investigation collected from June,2001 to July,2003.The soil moisture in layers of 0-10cm,10-20cm,20-40cm, 40-60cm,60-80cm,80-100cm was measured at an interval of 20 days.All the data were categorized by cropping patterns and gradients and in-depth analyse the spatio-temporal variation of soil moisture under different cropping patterns and gradients basing on methods of the traditional statistics.To analyse the seasonal dynamics of water in yellow soil,the traditional time-sequence model(ARMA) was applied in stochastic simulation and wavelet analysis(Mexican Hat) was described the periodic oscillation and singularity of soil moisture.To analyse the the temporal variation of water in yellow soil,geostatistics was applied to ensure the influence factors.The main achievements of this study are as follows:(1) The water content of yellow soil varies from season to season.There is adequate water supply to yellow soil during summer and autumn while less water supply during spring and winter. The variation of yellow soil moisture with time tends to be an same oscillation of wave.Spring is the season with high evaporation leading to soil moisture moving downward clearly,and the soil moisture is at the negative phase,which is disadvantageous to shallow root crops.Summer and Autumn are the accumulation stage of soil moisture from infiltration of rainfall and the soil water moving downward,at this stage the soil water content is at positive phase.Winter is the low evaporation and accumulation stage of soil moisture and the soil water content alternates between positive and negative phases.(2) There is large difference of yellow soil moisture within vertical profile.The content of soil moisture increases gradually as soil is deepened.Under different cropping patterns,spatial variability of the 0-10cm and 80-100cm depth is in a high degree which is affected by random parameters,while there is little operationtion of human in the 10-80era depth.Under different slopes,spatial variability of the 0-10cm depth is in a highest degree which is affected by random and structural parameters.There is a similar seasonal distribution of periodical characteristics between the adjacent layers in yellow soil profile,namely,the content of soil moisture is climbing in summer and autumn which is descending in spring and winter.Loose surface soil,poor water-holding capacity, high-viscosity lower soil strata and poor permeability are the main influence of the spatial variation on soil profile.(3)In the same external environmental condition,slope and cropping are important influence factors of the spatio-temporal variation of soil moisture.Under different gradient,the content fo soil moisture is 9.5°＞16°＞6.5°,and singularities happen in spring and summer.In spatial analysis, the variation is the most prominent in 20-100 cm depth of the 6.5°.the different mechanical composition is the main reason of abnormal character.Cropping patterns between corn-wheat and vegetable-vegetable make for the variation of soil moisture,which represents corn-wheat>bare land> vegetable-vegetable,and singularities happen in spring and autumn,especially in the cropping pattern of corn-wheat.In the analysis of spatial variability,Gaussian is used to model the bare land which is affected by random factors and structural factors.While,Spherical and Exponential are used to model the cropping patterns of corn-wheat and vegetable-vegetable respectively,the biomass of various crops and farming management result in the variation of soil moisture.