Abstract
Soil water experiments were conducted to determine the water supplying characteristics of two clayey Ultisols, a clayey Oxisol, and a sandy Oxisol. Water infiltration into all soils was very rapid, reaching 9 cm/hr after 1 hr of continuous flooding. The strong structural stability of the clay soils permitted infiltration rates in excess of that for the sandy soil. Lateral water movement, downslope, was a significant factor in observed high rates of water infiltration and may partially account for downslope movement of nitrates. Values of soil water tension after 2 to 3 days of free drainage did not exceed 20 to 80 cm of water (roughly 1/50 to 1/12 bar). Field capacity was established to be 1/15 bar for the sandy Oxisol and 1/20 bar for the clayey Oxisol and Ultisols. Two avenues of soil water movement were postulated: Capillary pores (between soil particles) and non-capillary pores (between soil aggregates). Because of water movement in non-capillary pores, flow characteristics of the clay soils resembled that of the sand. In terms of soil water release characteristics, the clays and the sand were similar.