EROSION AS AFFECTED BY TILLAGE–INDUCED ROUGHNESS AND SURFACE MULCH IN A SOIL WITH A SIMULATED SUBSURFACE PAN

Abstract

Soils with subsurface pan are subject to more rapid erosion compared with soils without a pan. The effect of tillage–induced roughness and surface mulching on soil loss and runoff in a sandy loam soil with a simulated subsurface pan was investigated under laboratory condition. A soil tray 0.75 m long × 0.5 m wide × 0.05 m deep, which was underlain by a plastic sheet, simulated an impermeable pan beneath the soil. A wire mesh was used to simulate treatments without a pan. The soil was manually tilled to create two roughness conditions, which were classified as harrowed (fine seedbed condition) and plowed (rough seedbed condition). Dried wheat straw was applied at a rate of 3 ton/ha in the mulched treatments. Simulated rainfall with intensity of 128 mm/h was applied to test the treatment effect. In soil with a pan, increased tillage–induced roughness led to a 50% reduction in soil loss compared with harrowed, bare soil. Similarly, application of surface mulch to the harrowed soil led to a 65% reduction in soil loss compared with the unmulched equivalent. Combining a rough surface with surface mulch led to 85% reduction in soil loss from the soil with a pan compared with harrowed, bare treatment. This reduction in soil loss from the plowed soil with a pan was comparable with that obtained from a similar treatment without a pan. Runoff from the panned soil was not affected by tillage or surface mulching. On the other hand, runoff was less in the soils without a pan compared to the panned soils. This preliminary investigation shows that through appropriate tillage with a good residue cover, sediment losses from panned soil can be reduced to the level obtained in soils without a pan. However, excessive runoff may still constitute a problem in panned soil unless a better drainage method is put in place.