SOME SELECTED SOIL PROPERTIES AND FERTILITY STATUS AS INFLUENCED BY AGRICULTURAL LAND USES OF ALFISOL IN AKURE, NIGERIA

Abstract

Anthropogenic land use often results to changes in soil properties such as structure, texture and fertility status. Most studies in the study area are concentrated on soil fertility status, while few studies have been carried out to investigate the flow properties and compaction characteristics of soil under different land uses. This study was conducted to investigate the effects of long-term land use on soil strength, hydraulic properties and fertility status of tropical Alfisol in Akure, Southwestern Nigeria. Three agricultural land uses namely; Cropland, Citrus orchard and Oil palm plantation were selected for the study. A completely randomized design was adopted in each site and soil was sampled at three varying depths (0-15 cm, 15-30 cm and 30 – 45 cm) with four replicates to give a total of thirty - six (36) samples for the three land uses studied. Separate undisturbed soil samples were taken from 0 - 45 cm depths at 15 cm increment with a steel core sampler of 5 cm diameter and 15 cm height for bulk density and shear strength determination. The hydraulic conductivity and soil water sorptivity were determined using mini disk infiltrometer at a steady - state flow of – 0.5, – 1 and – 2 cm water suction rates. Soil physical, chemical, hydraulic and mechanical properties were determined using standard procedures in order to evaluate the effects of different land uses. Land use significantly affected the physical, chemical, hydraulic and mechanical properties of the land use types (p ≤ 0.001, p ≤ 0.01 and p ≤ 0.05). The dominant textural class of soils of the experimental sites is sandy clay loam. Accumulation of silt and clay was observed in the sub-surface layers with a simultaneous decrease in sand content. Soil pH values obtained in all the land use systems are within the moderately to slightly acidic range. SOM content was highest (4.23%) under the Citrus orchard and lowest (1.84%) on the cropland. Higher average SOM (3.84%) was observed in the surface (0-15 cm) soil layer than subsoil (15 – 30 cm and 30 – 45 cm) layers. Citrus orchards on the overall accumulated more organic matter content, total nitrogen, available phosphorus and thus increased cation exchange capacity than other land use types. Results showed that exchangeable cations, exchangeable acidity and cations exchangeable capacity decreased with depth increment in all the land uses. It was observed that soil nutrients vary from one land use type to another. Citrus orchards have the highest mean value of Fe (22.44 mg/kg) followed by oil palm plantations (15.09 mg/kg), while cropland has the lowest mean value of 7.72 mg/kg. The hydraulic conductivity value showed an increasing trend from the citrus orchard to cropland and oil palm plantation in the order citrus orchard (4.72 cm h-1) < cropland (10.80 cm h-1) < oil palm plantation (13.12 cm h-1). Citrus orchards recorded the highest mean soil water sorptivity value, while oil palm plantation had the least value. Considering the interaction effect of land use types and soil depths on soil strength, it was observed that in both methods adopted (unconfined compression test and vane shear test) citrus orchards had the highest average shear strength among the land use types down the soil depths. Soil management has a significant impact on agricultural productivity and ecosystem sustainability as soils differ in their response to different management. Thus, understanding of soil fertility status and hydraulic conductivity in relation to the strengths of soil are very important in agricultural soils since the penetration of plant roots into soils for obtaining water and nutrients depends on the strength of the soils.