Physical changes induced by rainfall in the surface layer of an alfisol, Northern Nigeria

Abstract

Periodic measurements of bulk density, porosity, aggregate sizes, penetrability and infiltration were made to assess physical changes induced by rainfall in the surface layer of an Alfisol under the following treatments: undisturbed and bare, bare with frequent shallow cultivations and a 7-cm thick layer of grass mulch. The treatments were imposed after initial tillage. Physical changes in the 0–3 cm layer of the unmulched plots occurred rapidly during the first rains. In the first 5 weeks after tillage, bulk density increased by an average of 0.09 g/cm 3 per 50 mm of rainfall, and aeration porosity at a suction of 100 cm decreased by over 70%. Large aggregates were also broken down into smaller ones; by the end of the season the proportion of aggregates > 0.25 mm decreased from 40 to 23%. Infiltration rates declined wit h time and by the end of the season were down to 25% of their initial values in the bare plots. Surface layers had undergone evident hardening as well. Periodic hoeing kept the surface layer in better physical condition than did hand-weeding alone. Aggregation remained greater, surface hardening lower, and infiltration rate higher in the hoed plots. In contrast to the bare plots, the mulched plots retained favorable physical conditions in their surface layers throughout the rainy season.