Agricultural Land-Use Effects on Soil Cation Exchange Capacity, Organic Carbon and Total Nitrogen in Soil Aggregate Sized Fractions in Ile-Ife, Nigeria

The study determined the distribution of organic carbon (OC), cation exchange capacity (CEC) and total nitrogen (TN) associated with soil aggregates across land-use types in Ile-Ife, Nigeria. Six agricultural land-use types were considered which were undisturbed secondary forest, continuously cropped land, paddock, oil palm, cocoa and teak plantations at the Teaching and Research Farm, Obafemi Awolowo University, Ile-Ife, Nigeria. Soils samples were randomly collected from each land use at 0-15 and 15-30cm soil depths in three replicates. The samples were segregated into four aggregate classes; <63µm, 63-250µm, 250µm-1mm and 1-2mm respectively. The following analyses were carried out on the whole soil: particle size distribution, soil pH, CEC, OC and TN while CEC, OC and TN were carried out on different soil aggregate fractions. Data obtained were subjected to analysis of variance using SAS software and means were separated using Duncan’s Multiple Range Test at p ≤0.05. Results showed that OC, TN and CEC were more associated with smaller sized soil aggregates (<250µm) across all the land-use types, except under oil palm plantation, which had most of its SOC associated with 1-2mm sized soil aggregate. In the whole soil, continuously cultivated land had the least OC and TN while secondary forest surprisingly had the least CEC. The study revealed that aggregate size <250µm contributes the most to soil nutrient available. Therefore, conservative land-use practices (such as conservative tillage, mulching, manuring etc.) that protect the loss of soil micro-aggregates (<250µm) especially to erosion should be adopted for sustainable land-use.