Abstract

Jerry A. Ngailo and Sonia F. C. Dechen

Studies of size distribution, stability of the aggregates, and other soil properties are very important due to their influence on tilth, water infiltration, and nutrient dynamics and more importantly on accelerated erosion but are affected by soil surface management. Both chemical e.g. pH, organic carbon, (OC), exchangeable cations e.g. calcium (Ca), magnesium (Mg) and physical properties such as aggregate size and stability are dynamic properties, which vary in response to forces affecting soil environment. This study was carried out to have a long and detailed understanding of how artificial surface soil covering materials can protect the soil physical and chemical properties from the ravages of soil erosion. Such endeavor would allow us to make suitable modification to soil conservation practices to enhance soil stability and importantly soil productivity. Data measured for eight years on induced erosion experiments on a Ferralsol covered by artificial soil netting locally called sombrite at Campinas, Brazil, were used to examine the effects of accelerated soil erosion on soil chemical and physical properties. Each erosion plot had an area of 25 x 4 m. Four soil treatments were chosen: bare (control) and three artificially covered soils. Changes of soil properties observed in relation to aggregation were bulk density, total and aeration porosity, available water capacity and changes in soil chemical properties. From pooled data stepwise multiple regressions were done to find out the relationship of aggregate stability with pH, calcium, and organic matter. There were no significant differences (P=0.05) in mean weight diameters (MWD) and size distribution irrespective of whether samples were collected from the upper middle or lower parts of the erosion plots. There were very gradual decline in mean weight diameters (MWD) and size distribution of water-stable aggregates during the study period. Bulk density increased appreciably on bare soils but remained almost constant in artificially covered soils. However, using Duncan tests, the treatment differences were not significant (P=0.05). Non-significant correlation (P=0.05) between MWD and the soil chemical properties were observed. Coefficients of determination for pH, OC, MWD and Ca could not sufficiently assist in explaining changes in aggregate stability as a result of surface cover.