Effect of Water Regime on Aggregate-tensile Strength, Rupture Energy, and Friability

Summary

The effect of water regime on aggregate-tensile strength, rupture energy, and friability index was studied in two experiments on sandy loam soils (Glossic Phaeozem/WRB 1998). In Exp. 1, soil from a long-term, 5-yr crop rotation receiving animal manure (dairy farm and grass, DFG) was compared with a soil (continuous cereal crop, CCC), which had grown almost continuous cereals and not received animal manure. In Exp. 2, soil from compacted plots (PAC) and uncompacted reference plots (REF) was sampled. The soil was air-dried and separated into four aggregate-size classes (i.e., 1–2, 2–4, 4–8, and 8–16 mm). Aggregate-tensile strength and rupture energy were measured on air-dry aggregates and on aggregates adjusted to -10, -30, -100, -350 kPa, and -166 MPa pressure potential. Soil friability index was estimated from the tensile strength or specific rupture energy results. Aggregate density was determined on 2- to 4-, 4- to 8-, and 8- to 16-mm aggregates. The CCC soil displayed a greater increase in strength and specific rupture energy with increased dryness than the DFG counterpart. This may be related to differences in organic matter content and dispersible clay. Generally, the relationship between tensile strength or specific-rupture energy and pressure potential could be described by a power function. However, the rupture energy results could not be fitted by a power function for the Exp. 2 soils. The Exp. 2 soils differed in the stress–strain relationship, i.e., the compacted soil displayed the highest Young modulus, (Y/ ) in all cases. Maximum values of the friability index were found between -10 and -100 kPa.