Water Transport Through Interface Between Land And Atmosphere In Dry Season On Red Soil Slopes

Water resource is very rich in red soil regions of China . But for the dramatic changes and spatial unbalances of rainfull in these regions, the agricultural sustainable development of this land is usually obstructed. Based on Taoyuan Agro-ecological Experimental Station, Chinese Academy of Sciences, water transport processes through soil-atmosphere and leaf-atmosphere interface and their relationships with the environmental conditions were studied on red soil slopes tea plant, the aim was to find out the response characteristics of plant to seasonal drought, and to search the approaches for regulating the interface processes and to provide the theoretical and practice basis for avoiding from or fighting against drought during the agricultural exploitation of red soil slopes. Through the experiments, the main results were obtained as follows:l.When the effects of crop was neglected, seasonal variation of water transfer flux of soil-atmosphere interface was affected significantly by raicroclimatic and soil surface (0-20cm) water contents. Correlation analysis suggested that the correlation coefficients between soil evaporation under crop canopy and air temperature, leaf temperature, relative humidity were highly significant (0.63**, 0.76**, -0.61**, n=19) ; the correlation coefficients between soil evaporation under crop canopy and net radiation, soil surface temperature, sunlight hour were significant (0.48*, 0.50*, 0.51*, n=19). When the LAI was 2.2 on red soil slopes, the function of relative evaporation (E/ET0) to soil water content(S) was as follow: E/ET,,=1. 1807+0. 3876LnB, R2=0. 6009, P<0. 01.2. Stmomatal behavior had the mechanisms of respond to environment change. The daily variation curve of stmomatal resistance was W form in drought condition, and the daily variation curve of stmomatal resistance was ti form in wetness condition, and stmomatal resistance in drought condition was more than that of in wetness condition. Multi-regression results of stmomatal conductivity and light intensity, air temperature, relative humidity suggested that plurality correlation coefficients (R) and F test were highly significant level (R=0. 702, F=15.21, P<0.01), t test of deflectioncorrelation coefficients revealed that every factors affected stmomatal behavior significantly. Daily variation of transpiration rate of the tea plantation appeared in a shape of inverted saddle, low in the morning and evening and high at noon, and the shape of the inverted saddle was changed from day to day. The transpiration rate was subjected to a number of micro-meteorological factors on the tea plantation. Correlation analysis and multi-factor successive regressional analysis revealed that net radiation and water vapor saturated deficit were the two major meteorological factors affecting transpiration of the tea plants. Transpiration rate was closely related to leaf stmomatal conductivity. The former increased with the rise of the latter.3.The distributive characteristics of energy balance suggested that water and energy transport through interface between land and atmosphere was affected significantly by soil moisture. Soil moisture played an important role in latent and sensible heat transfer. The drier the soil, the higher the sensible heat flux and the smaller the latent heat flux, and vice versa. The distributive characteristics of water balance suggested that the soil conserved water occupied about 58. 5% of total precipitation on tea plantation (LAI=2.2), and surface runoff occupied about 20%. Vapor flux through interface between land and atmosphere decreased significantly in soil-water stress condition. During the observation, neglecting the evapotranspiration of rainfall process, evapotranspiration was 60. 02mm more than homochronous precipitation, which was the major reasons of seasonal drought in red soil regions. The ratio of water which lost directly to the atmosphere without through plant body to the total field evapotranspiration was 32%, which illustrated the water-saving regulation potential on soil-atmos...