Monday, November 13, 2006

Water Balance for Cotton Grown with Reduced Tillage on Coastal Plain Loamy Sand.

Warren Busscher1, Philip Bauer1, E. J. Sadler2, and Dean Evans1. (1) USDA-ARS, Coastal Plains Research, 2611 W Lucas St, Florence, SC 29501-1242, (2) USDA-ARS CS&WQRU, Univ of Missouri, Ag Eng Bldg, Room 269, Columbia, MO 65203

Even though rainfall can be abundant in the SE Coastal Plain, soils can be droughty because of low water holding capacities. A Sentek frequency domain reflectometry sensor was used to measure distribution of rainfall that infiltrated into the soil and was taken up by roots of cotton grown in reduced tillage. Sensors measured volumetric soil water content at 0.5 h time intervals and 10-cm depth intervals to 1 m. Changes of soil water content were separated into infiltration, evapotranspiration, deep percolation, and runoff using rain gauge measurements and software written specifically for this experiment. At mid-season, cumulative infiltration was 75 to 85% of the rainfall with spikes up to 90% during storm peaks when water ponded on the soil surface. Later in the season, during an unusually active tropical storm season, cumulative infiltration dropped to 60% because the profile was wet, unable to accept as much infiltration. Evapotranspiration was measured as reduction of soil water content that did not drain deeper into the profile; it was highest in the top 30 cm and decreased exponentially below that. Even though the soil dried out easily and was disrupted deeply under the row, most water for plant growth came from the top 30 cm..