Soil management systems based on soil quality at three different toposequences in cross river state, South-Eastern Nigeria

The morphological, physical and chemical characteristics of three toposequences were studied in order to offer suggestions on soil management systems that would increase crop production in South-eastern Nigeria. The study was conducted at the upper slope, middle/lower slope, and valley bottom on three parent materials, namely, basement complex (BC), sandstone and sandstone/shale. The Ap horizon was generally shallow. A hue of 7.5YR typified the landscapes, and colour value ranged from light-brown to brown. Low chroma in the matrix and high value mottles were common in the valley bottom. The soil profiles were similar in soil structure and consistency, generally weak, medium sub-angular blocky and friable topsoil to very sticky and very plastic subsoil. Sand was the dominant particle-size fraction. Soil texture was either sandy loam or loamy sand overlying sandy clay or sandy clay loam. Soil density varied with the soil profiles. Macropores were generally greater than 50% of total pore space. Saturated hydraulic conductivity (Ksat) was 2.16, 1.50 and 1.28 cm h-¹ in the respective toposequences. Water stable aggregates > 2.0 mm averaged 28.8%, 26.5% and 33.5%, while >0.5mm averaged 52.1%, 60.1% and 51.5%, respectively in the topographic positions of the toposequences. The soil profiles were slightly acidic. Soil organic C, averaged over all toposequences was 11.6, 12.5 and 10.5 g kg-¹, while available phosphorus was 9.32, 6.77 and 20.04 m kg-¹, respectively. Similarly, CEC averaged 7.21, 10.61 and 12.48cmolkg-2, while base saturation was 45.4%, 67.8% and 78.6%, respectively. Based on the soil characteristics, three soil management units (SMU) were identified as SMU A (Upper slope), SMU B (Middle/lower slope) and SMU C (Valley bottom). The corresponding soil management systems (SMS) are dry land farming with agroforestry and planted fallow in SMU A, wetland and dry land farming in SMU B, and wetland, and wetland/dry land farming in SMU C. These SMUs and SMS will facilitate the use of the soils on the slopes and lead to an increase in crop production and farmers’ income in the study area and other areas with similar soil and ecological conditions. These SMS are being recommended for use by agricultural extension agents to assist farmers cultivate their sloping lands in a more efficient and productive manner.