Unraveling the relationship between rural farm household wealth, carbon storage, and soil quality in Namibia's Zambezi Region

A significant portion of smallholder farming systems in Sub-Saharan Africa are marked by significant heterogeneity in both biophysical and socio-economic conditions. Resource access and the patterns of resource allocation at household level are often co-determined by wealth. We hypothesized that wealth plays a pivotal role in the effect of future-oriented farm management on soil organic carbon storage (SOC) and soil quality. To test this hypothesis, we conducted a study involving 42 households categorized in three wealth classes (high, medium, low) based on farm-household survey data from the Namibian Zambezi region. Soil samples were collected up to a depth of 1 m with a focus on soil organic carbon and nitrogen throughout the soil profile. Topsoils were additionally analyzed for texture, cation exchange capacity (CEC), pH, and available phosphorus; field size was measured. A follow-up survey wave captured information on crop species, yield, and soil management practices.

Results of the survey showed, that farmers of our study area typically burn their field regularly before the cultivation period. With rare exceptions no farmer fertilized their fields, neither with mineral fertilizer nor with manure. Results indicated that relatively wealthier farmers had larger fields, yet intriguingly, their yields per hectare were not higher than for farmers in lower wealth terciles. Notably, the Arenosols, which are widespread in the Zambezi region, had lower sand and higher clay and silt contents among the relatively wealthier farmers. Moreover, high wealth class showed significantly higher soil organic carbon and nitrogen concentrations in the topsoils compared to medium and low wealth classes along with CEC values. Though, no such a trend was observed for available phosphorous and pH. The elevated levels of soil organic carbon and nitrogen of relatively wealthy farmers persisted consistently up to a depth of 1 meter. These results indicate that the soils of farmers in the high wealth class have inherently better soil conditions. Contrary to our hypothesis, the wealthier farmers did not seem to invest more in land management in order to improve soil conditions. Instead, historically they seem to have been more inclined to settle on the more fertile soils in the Zambezi region of Namibia and benefit from larger fields and thus higher quality natural resources.