SURFACE MEASUREMENTS OF THE HYDRAULIC-PROPERTIES OF A TILLED AND UNTILLED SOIL

The surface characteristics of soil can have a profound effect on the hydrology of tilled land. Apposite measurements of the surface hydraulic properties of Plainfield sand (Wisconsin, U.S.A.), a Typic Udipsamment, were used to assess the hydrologic impact of 5 years tillage by either moldboard plow or no-till. The crop was always corn (Zea mays L.). The "mean" pore size (λm), weighted in a way relevant to the flow of water through the soil surface, was computed here from saturated and unsaturated measurements of sorptivity (S0) and hydraulic conductivity (K0). Disc permeameters of dissimilar radii were used at two unsaturated supply-potential heads of ψ0=-100 mm and -20 mm to find S0 (ψ0) and K0 (ψ0). At saturation (ψ0=0), infiltration rings of contrasting radii were employed. The saturated and unsaturated values for S0 and K0 of the plowed soil were either the same as, or greater than the corresponding values for the no-till soil. Combination of the values for the saturated S0 and K0 showed that the no-till soil had a λm=1.34 (±0.67) mm, while in the plowed soil the "mean" pore size during saturated flow was only 0.19 (±0.18) mm. The large λm, and the high coefficient of variation, for the no-till soil was presumed to be related to the macropore network associated with the decay of crop residue in the less-sorptive matrix. The small homogeneous λm of both the saturated and unsaturated plowed soil reflects the annual pulverization of the soil surface by tillage. © 1990.