Soil aggregation, and total and particulate organic matter following conversion of native forests to continuous cultivation in Ethiopia.

摘要

Conversion of native forests to cultivation is usually accompanied by a decline in soil organic carbon (SOC) and nutrients, and deterioration of soil structure. The objectives of this study were: (i) to assess the effect of cultivation on soil aggregation and aggregate stability and (ii) to determine the effect of cultivation on total SOM, and the quantity and quality of POM in a Rhodic Nitisol at Munesa, in southeastern Ethiopia. Samples were collected from a cropland cultivated for 26 years and an adjacent natural forest. After cultivation, the proportion of water-stable macroaggregates was significantly reduced from >70% in the natural forest soil to 50% in the cultivated soil, being more pronounced in the >1 mm size aggregates. Cultivation also induced significant losses of OC and N both in bulk soil and water-stable aggregates. The amounts of free light fraction (free LF) C and N were more affected by cultivation than the amounts of intraparticulate organic matter (iPOM) C and N. The effect of cultivation was more pronounced on macroaggregate associated total and particulate organic matter than on microaggregate-associated fractions. The losses of POM C and N due to cultivation were highest in comparison to the total aggregate and whole soil OC and N suggesting that POM constitutes a more sensitive SOM fraction to the effects of cultivation. Soil aggregate stability and SOM could be used as indicators to apply the more appropriate management practices for increasing soil sustainability or productivity..