Slope Position and Land Use Effect on Select Soil Properties, Quality and Carbon Stock in Surface Soils at Afaka Forest Area, Northern Guinea Savanna of Nigeria

Abstract

Population increase and the need to achieve food security; especially in Nigeria, necessitated encroachment into forests and marginal lands for agricultural land uses in the Savanna ecologies. However, tropical soils are inherently fragile and prone to rapid degradation under intensive agriculture; especially when soil cover is removed and the soil tilled conventionally. Also, Savanna Alfisols are low in inherent fertility, organic matter, cation exchange capacity, dominated by low activity clays and sesquioxides. The increasing incidence of soil degradation and nutrient impoverishment of the savanna ecologies resulted in deceasing soil quality, agricultural production and increasing farmer food insecurity that generated interest in the need to evaluate effect of slope and Land use on soil properties, quality and carbon stock on Afaka soils in Nigerian Guinea Savanna. Data generated were analyzed using ANOVA and significant means were determined using Duncan multiple range test (DMRT). Results obtained reveal that cultivation activities and erosion accounted for increased silt (19.10 %) in cultivated areas than forest areas (14.89%), while sand fractions (54.44%) dominate separates in the Forest and the Cultivated land uses. Upper slope positions had the highest sand content (71.67%), followed by lower slope with 68.00%, and then middle (67.67%) slopes. Silt contents at the middle slope positions were significantly higher than at upper (15.33%) and Lower slope Position (17.00%) and clay values increased in the lower slope terrains. Also, organic carbon varied significantly between the land use types and slope position on the toposequence. At the forest areas, organic carbon was 10.2 gkg-1 and higher significantly than Cultivated fields (8.2 gkg-1). At the upper slope fields under cultivation, organic carbon value was 8.7 gkg-1 and was significantly lower than Middle slope (9.60 gkg-1) and Lower slope terrains (6.30 gkg-1). Under Forest land use also, Middle slope terrains had significantly higher organic carbon content than Upper slope terrains. The high Carbon stock of the forest middle slope terrain (1.77 tCha-1), followed by forest land use type would discourage global warming and climate change within the Afaka environment However, carbon stock in forest Land use type in Afaka areas (1.41 tCha-1) was significantly higher than cultivated land use types (1.21 tCha-1). At cultivated slope terrains, middle slopes retained significantly higher SOC (1.37 tCha-1) than upper and lower slope terrains. Considering soils for prime quality, soils under forest lower slope terrain ranked best quality (SQ1; prime quality) for sustainable cultivation purposes, followed by cultivated middle slope and forest land use type that ranked SQ2. Cultivated upper slope soils ranked least (SQ6) in quality for use in crop production, while cultivated lower slope and cultivated land use type soils ranked SQ5. However, increasing loss of forests to intensive cultivation activities without adequate soil management practices would portend increase in global warming and climate change in the study area.