Soil organic carbon concentration and stock of arable land use of two agro-ecological zones of Nigeria

Abstract

Soil Organic Carbon (SOC) dynamics study in arable land use at different agro-ecological zones is important for recommendation of sustainable land use management practices against detrimental practices. This will provide insight on how to enhance SOC sequestration, improve soil quality and mitigate impact of climate change in different agro-ecological zones. This study was conducted at two agro-ecological zones of Nigeria; upland rainforest (Ado-Ekiti) and southern guinea savanna (Kabba) to evaluate SOC sequestration under arable land use. From the two agro-ecological zones, 1 ha (ha) of land was marked out, five soil samples were randomly collected at four different depths (0–15, 15–30, 30–45, and 45–60 cm) for SOC sequestration study. Higher SOC concentration and stock were observed at Ado-Ekiti site over Kabba site was due to best soil management practices like soil organic and inorganic fertilizers application and incorporation of crop residues. SOC concentration distribution varied greatly (%CV > 35%) and decreased with depth at the two agro-ecological zones. SOC stocks ranged from 6.59 t ha −1 to 24.97 t ha −1 and decreased with depth in similar trend with SOC concentration. Generally, at both sites, soil organic matter (SOM), total nitrogen (TN), available phosphorus (AP) decrease with increasing depth especially to 45 cm depth while soil pH increase with increasing depth. Both SOC concentration and stock were observed to have significant positive correlation ( P < 0.01; P < 0.05) with SOM ( r = 1.000** and 0.996**; and r = 0.991** and 0.707**) and TN ( r = 0.936** and 0.934**; and r = 0.992** and 0.691**) at Ado-Ekiti and Kabba sites respectively. This indicated that increase in SOM and TN were associated with increase in SOC stock and concentration. Maximum value (20.33%) of exchangeable sodium percentage (ESP) of above critical value of 15% was recorded at Ado-Ekiti site which requires that soil be managed against sodicity. There was significant difference ( t = 2.975**) between the overall mean SOC stocks (14.83 and 9.15 t ha −1 at Ado-Ekiti and Kabba sites respectively) at two agro-ecological zones. Thus, adoption of better soil management practices will enhance SOC sequestration and soil quality at the two agro-ecological zones.