Soil fertility evaluation and land-use effects on soil properties, carbon and nitrogen sequestration in the rainforest of Nigeria

Abstract

This study investigates changes in soil properties, specifically soil organic carbon (SOC) and total nitrogen (TN), associated with different land use systems derived from forests in the rainforest zone of Nigeria. The land use systems examined include mature oil palm plantation (OP), bush fallow or secondary forest (BF), alley cropping with multi-purpose trees (AC), and continuous cassava cropping with and without fertilizer (FC and UC). Converting forests to cultivated land led to a decrease in SOC and TN content and storage across all soil depths (0-10 cm, 10-20 cm, and 20-40 cm). In the top 0-10 cm depth, the average decrease in SOC and TN storage was 63% and 62%, respectively, while for 0-40 cm, the decrease was 48% and 46%, respectively, for all land use systems derived from forests. Furthermore, the study reveals that even after 5, 10, and 30 years of secondary forest regrowth (BF), alley cropping (AC), and oil palm plantation (OP), respectively, the fertility levels were not restored to those observed in the primary forest. These findings underscore the capacity of forest soils to conserve and enhance soil SOM (soil organic matter), which in turn plays an essential role in SOC sequestration, TN storage, and soil nutrient conservation.