The impact of land use on soil carbon in Miombo Woodlands of Malawi

Abstract

In the Miombo Woodlands Region of south-central Africa, it is estimated 50–80% of the total system's carbon stock is found in the top 1.5 m belowground. Deforestation and rapid population growth rates have led to reduced fallow periods and widespread land degradation in the south-central Africa area of the Miombo Woodlands. The impact of this land use conversion on belowground carbon and nitrogen stocks within the Miombo Woodlands has not been examined extensively in the past. We addressed how the soil carbon profile reacts to conversion to agriculture, the continuation of agriculture, and the ability of the soil carbon budget to recover following abandonment within the Chimaliro Forest Reserve and surrounding villages in Kasungu, Malawi. Protected natural Miombo Woodlands sites, agricultural fields of increasing ages, and fallow fields of increasing ages were sampled. Surface carbon levels in Miombo soils varied from 1.2 to 3.7%. Agricultural soil carbon was significantly depressed with surface layers ranging from 0.35 to 1.2% carbon. Unexpectedly, fallow carbon and nitrogen levels continued to be significantly repressed (surface soils 0.65–2.3% C), pointing out the possible unsustainability of the current agricultural management cycle dominant in the area. On average, agricultural soils contain 40% less soil carbon than the natural Miombo Woodlands. Soil carbon declined logarithmically with depth within all land use types. Clay content was significantly positively correlated with soil carbon in the top 40 cm and therefore areas of higher clay content contained elevated carbon levels. Although a common attribute to many agricultural systems, bulk densities were not significantly altered by land use changes.