Impacts of land‐use changes on soil fertility in Okomu Forest Reserve, Southern Nigeria

Abstract

AbstractThis study assessed changes in soil properties and soil fertility resulting from land‐use conversion from rainforest to oil palm and rubber plantations in Okomu Forest Reserve, Southern Nigeria. We collected 315 soil samples at 0–15, 15–30, and 30–60 cm and analyzed soil physicochemical properties. In addition, soil fertility index (SFI) was computed using the analytical hierarchical process. Our results showed that soil organic carbon declined by 40% and 60% (0–15 cm), 32% and 57% (15–30 cm) and 33% and 57% (30–60 cm) in oil palm and rubber plantations, respectively. Similarly, total nitrogen also declined by 43% and 56% (0–15 cm), 34% and 36% (15–30 cm), and 36% and 41% (30–60 cm) in oil palm and rubber plantations and was significantly lower in plantation soil than in the rainforest soil. Soil organic carbon and total nitrogen were, however, higher under oil palm than rubber plantations. In contrast, available phosphorus was higher under rubber plantations than oil palm plantations. The mean values of soil exchangeable potassium and sodium are significantly lower in the rainforest samples. Generally, SFI ranged from 7.30 to 20.46 in the rainforest, 4.16–13.21 in oil palm and 5.15–8.03 in rubber plantations. We conclude that soil degradation is more severe in oil palm plantations than in the rubber plantations. This implies that in addition to site‐specific management, species‐specific management strategy must also be developed to ensure sustainable utilization of soil resources in deforested rainforests.