SOIL WATER RETENTION AS RELATED TO TOPOGRAPHIC VARIABLES

Authors: Pachepsky, Yakov; Timlin, Dennis; Rawls, Walter

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/1/2000
Publication Date: 3/1/2001
Citation: N/A

Interpretive Summary: The ability of soils to retain water has often to be estimated rather than measured. This has usually happened when a project is small, when a design or a research is preliminary, or when the area is large so that measurement becomes impractical. User groups of these estimates include engineers and researches in many disciplines such as hydrology, agronomy, meteorology, ecology, and environmental protection. Presently, soil basic data availabl from soil surveys are used to estimate soil water retention. Contents of soil textural components are the most popular as the input data for the estimates, although other soil properties such as bulk density, organic matter content, structural indexes, are also often used. Development of the site-specific agriculture has posed a new challenge for estimating soil water retention because the variation of soil basic data is not usually known within agricultural fields. Therefore, new types of input data for the water retention estimation need to be explored. We proposed to use the topographic variables for that purpose. This study evaluated the variability of texture and water retention of soils for a gently sloping 3.7 ha field located in the long-term precision farming research site at the Beltsville Agricultural Research Center, Maryland. Sand, silt, and clay contents along with soil water retention at 10 and 33 kPa showed dependencies on slope and curvatures. The regression model relating water retention to the topographic variables explained about 79% of variation in soil water content and was as accurate with the validation data as with the development data. Results of this work show a potential for the topographic variables to be used as interpretive variables for yield maps in precision agriculture.

Technical Abstract: Digital elevation models were proposed and used as a data source to estimate soil properties. This study evaluated the variability of texture and water retention of soils for a gently sloping 3.7 ha field located in the long-term precision farming research site at the Beltsville Agricultural Research Center, Maryland. The specific objectives of this research were to (a) characterize the variability of the water retention across the hill slope and (b) determine and describe any correlations of soil water retention with soil texture and surface topography. Soil was sampled along four 30m transects and on a 30m grid. Textural fraction contents, bulk density, and water retention at 2.5, 5.0, 10, 33, 100, 500, and 1500 kPa were measured in samples taken from 4-10cm depth. The 30m digital elevation model was constructed from aerial photography data. Slopes, profile curvatures, and tangential curvatures were computed in grid dnodes and interpolated to the sampling locations. The group method of data handling was applied to relate water retention and texture to the computed topographic variables. Sand, silt, and clay contents showed dependencies on slope and curvatures. Soil water retention at 10 and 33 kPa correlated well with sand and silt contents. The regression model relating water retention to the topographic variables explained about 79% of variation in soil water content, and was as accurate with the validation data as with the development data. Results of this work show a potential for the topographic variables to be used in interpretation of the field-scale variability of soil properties, and, possibly, yield maps in precision agriculture.