Physical and morphological characterization of undisturbed and disturbed ploughpans in a sandy loam soil

Abstract

In a sandy loam soil the ploughpan had a lower porosity and a higher bulk density and mechanical resistance than ploughpans that had been disturbed by rota-digging two years previously. Hydraulic conductivities ( K) for pressure heads ( h) from 0 to −20 cm were higher and moisture contents within the same h range were lower. Both values were identical for pressure heads lower than −20 cm. According to the widely used physical capillary pore model, the volume of pores > 140 μm was 2% (v/v) in the undisturbed ploughpan and 8% (v/v) in the disturbed ploughpan. However, micromorphometric analyses showed that the undisturbed ploughpan contained the highest volume of large pores and many continuous root channels, while the disturbed ploughpan had no continuous large pores. Pore continuity was determined by using a staining test with methylene blue. Disturbance of the ploughpan in these soils results in formation of unstable fragments, which collapse, thereby disrupting the vertical continuity of the initially large packing voids between fragments.