Tillage effects on measured soil hydraulic properties

Abstract

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 measurements 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 ( α = 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.