TILLAGE EFFECTS ON MEASURED SOIL HYDRAULIC-PROPERTIES

The effect of no-tillage (NT), ridge tillage imposed on long-term NT (NT/RT), moldboard plow (MBD), and chisel tillage (CHT) treatments on soil water retention and movement on three soils was studied using field and laboratory measurements. Field measurements of saturated hydraulic conductivity (K(fs)) were made with a Guelph permeameter; laboratory measurements of saturated hydraulic conductivity (K(sat)) were made using the constant head method on 30 and 7.5 cm diameter cores. The geometric mean of K(sat) from 30 cm cores was greater in NT than in MBD for both the Ap and B horizons of Nicollet clay loam (fine-loam, mixed, mesic Aquic Hapludoll) and Rozetta silt loam (fine-silty, mixed, mesic Typic Hapludalf); however, K(sat) from 7. 5 cm cores was not significantly different for the two tillage treatments. The K(sat) for the Ap horizon of Seaton silt loam (fine-silty, mixed mesic, Typic Hapludalf) in NT/RT was lower than in CHT, possibly because of surface layer compaction produced during manure injection. A greater number and total area of stained macropores were found in NT than in MBD. Comparisons between methods of saturated hydraulic conductivity measurement showed that K(sat) values from 30 cm cores were the greatest for all treatments and depths, which may be attributed to the role of continuous macropores in large core samples. The K(fs) values obtained from the Guelph permeameter (alpha = 12 m-1) were smaller than K(sat) values from 30 and 7.5 cm cores. Unsaturated hydraulic conductivity was measured with a disk permeameter both in the field and laboratory. For water potential values from -30 to -150 mm, the unsaturated hydraulic conductivity (K(suc)) values were similar for the NT and the MBD treatments and were much lower than the K(sat) values. To include the effects of macropores, larger core samples are preferred.