Using automated soil water content measurements to estimate soil water budgets

The distribution of precipitation into the components of a soil water budget has a profound impact on crop growth, groundwater recharge, soil erosion, and groundwater and surface water contamination levels. The main objectives of this study were to develop a new method of measuring soil water balances and to demonstrate the use of the method in examining differences between partitioning of water in conventional tillage (CT) and no-tillage (NT) management systems. Hourly precipitation, evapotranspiration, and changes in soil water storage data were collected automatically over a 3-yr period at a field site near Elora, Ontario. Runoff and interception were calculated as the difference between measured increases in soil water storage and total rainfall during each significant rain event when the soil was not frozen. Drainage was then calculated, as it was the only component of the soil water balance not measured. The amount of soil water stored in the NT system was greater than the CT system during the latter part of the study as the NT system aged. The amount of drainage calculated for a 3 -yr period was greater for CT than the NT treatment, a result that is contrary to many previous studies. The measured amount of runoff plus interception was greater in the NT versus CT treatment. Since NT is generally accepted as a means of reducing runoff, this result could be due to the enhanced amount of interception by the crop residue left on the surface of the NT treatment. Key words: Soil water balance, water content reflectometer, drainage, runoff, tillage, time series