Duration of Cultivation Has Varied Impacts on Soil Charge Properties in Different Agro-Ecological Zones of Ghana

Abstract

Agricultural expansion into natural habitats causes soil fertility decline after a period of cultivation. This study investigated changes in soil exchange properties in different farm types at Dompem and Adansam in the Forest and Forest–Savannah transition zones of Ghana as influenced by the duration of cultivation. Sixty farms were selected for soil sampling through a reconnaissance survey. The soils were subjected to physicochemical analysis. The results showed that the Dompem soils were loamic, had more amorphous Fe and Al oxides, were strongly acidic and had low contents of exchangeable acidity, a low sum of exchangeable bases (SEB), low effective cation exchangeable capacities (ECECs) and low available P. Conversely, the Adansam soils were arenic, slightly acidic and had relatively higher SEBs and ECECs. Interestingly, soil organic carbon (SOC) in the Dompem soils declined by >10% in relation to the duration of cultivation and showed rapid reductions within three years. Correspondingly, soil bulk density, CEC and SEB declined. In Adansam soils, only δpH declined in relation to the duration of cultivation. Soil organic carbon accounted for >50% of the ECEC and 49% of the SEB in Dompem soils but 36% of δpH in the Adansam soils. In conclusion, agricultural expansion, manifested in the duration of cultivation, mainly influenced soil charge properties through SOC decline.

Differential Impacts of Cropland Expansion on Soil Biological Indicators in Two Ecological Zones

“…Our results present a picture of interactions between external environmental and edaphic factors categorized as eco-edaphic trends and farm trends, starting from a broad (reconnaissance survey) to a narrow (main study) level. The eco-edaphic trends present diverse edaphic conditions in each agro-ecological zone, particularly with regards to SOC, POXC, soil texture, and pH, as seen in this and previous studies [40,45] on the same study sites. For instance, the findings of the reconnaissance survey sites show that the wet zones (forest and deciduous forest) contained more SOC and POXC than the forest-savanna transition and two savanna zones.…”

“…This is because these trade-offs tend to vary with the type of ecosystem cleared, soil type, and crops grown, as well as soil and crop management practices employed [8]. Earlier research on farm types under agricultural expansion in the forest zone of Ghana showed a decline in SOC with farm age, which occurred along with a decline in soil charge properties [40]. This pattern differed from each of the two agro-ecological zones studied.…”

“…These include newly cleared native vegetation or fallow (one year), then three, five, and ten years of cultivation. Details of site selection, description, and sampling can be found in Figure 1 and in previous studies by Neina and Agyarko-Mintah [40] and Neina and Adolph [45].…”

“…Standard laboratory analyses were employed to measure basic soil properties, such as bulk density; particle size; pH in water and in KCl; total carbon (C), nitrogen (N), and sulfur (S); basic cation contents; exchangeable acidity; and pedogenic compounds, i.e., dithionite-citrate-bicarbonate and oxalate-extractable Al and Fe. The procedures were already described and reported by Neina and Agyarko-Mintah [40] and Neina and Adolph [45]. The soils contained no calcium carbonate.…”

“…Previous studies on the same sites and soils have already presented data on the basic properties of the reconnaissance sites in the various ecological zones [45] and two study sites [40], where more details can be found. The soils are sandier in the northern half and less sandy in the southern part of the country.…”