No abstract

Soil classification and suitability evaluation are requirements for attaining optimum utilization of the available land resources. Detailed soil survey of  a top sequence at Alabata, Southwest Nigeria was carried out using the rigid grid method. The soils were characterized, classified, and evaluated for rain-fed rice production. The results of the study showed that the soils were loamy sand to sandy clay loam texture, fine to coarse sub-angular blocky structure and loose to hard consistency. Soil reaction ranged from strongly acidic to slightly acidic (pH 4.2-6.1) with low organic carbon (5.6-19.0 g/kg) and total nitrogen (0.5-1.7 g/kg). The potassium contents were moderate while exchangeable cations and available phosphorus were  very low. Pedon 1 was classified as KandicPaleustalfs, pedon 2 as TypicHaplustalfs and pedon 3 as Aeric Kandiaqualfs. The index of current productivity (IPc) by linear model ranged between 8.7 and 10.3, while by square root models ranged between 16.2 and 17.5. The values suggested that the soils were not currently suitable (N2 and N1) for rice production. The index of potential productivity (IPp) ranged from 48.5 to57.0 by linear model and from 53.9 and 58.5 for the square root model. Thus, pedons were potentially marginally (S3) and moderately (S2) suitable for the production of rice. The limiting factors were mainly low levels of macro nutrients, organic matter and cation exchange capacity. Key words: Classification, climate, suitability evaluation, toposequence, rice production

The assessment of degradation status of wetland soils under five different land use types (LUTs) in Ogun state, Nigeria were studied. The laboratory study was conducted to determine the physical, chemical and biological properties of these wetlands and the results obtained were compared with the food and agriculture organization (FAO) standard indicators and criteria for land degradation assessment. The textural composition of the soil ranged from sandy loam to sandy clay loam. Total porosity was generally low with the mean value of 40.5%. The pH ranged from moderately acidic to slightly alkaline with fallow soil having the highest value. Available phosphorus was low across the LUTs. Total nitrogen was predominantly low in most of the cultivated soils to moderate in the fallow soils. Cation exchange capacity (CEC) was low, while the exchangeable sodium percentage (ESP) was high (>5) in all the LUTs. The organic matter ranged from low to moderate indicating low nutrients status of the soil. The soils were classified and placed in the order Alfisols. The degradation results showed that most of the cultivated wetlands were highly degraded compared to the reference (fallow) soils which were slightly degraded. It is opined that soil conservation practices like the use of inorganic fertilizers, organic manure, and composts should be intensified in these fragile low fertile wetlands. Also, there should be a periodic monitoring of the fertility status of the wetlands from the time it is first open for cultivation to subsequent uses.