SOIL CHARACTERIZATION AND LAND SUITABILITY EVALUATION

ABSTRACT

The land at Anuka, Nsukka Local Government Area of Enugu State in Southeastern Nigeria, under the sub-humid tropical climate was evaluated for maize (Zea mays), cassava (Manihot esculenta), yam (Dioscorea spp.) and oil palm (Elaeis guineensis) cultivation. Data were obtained by field study and laboratory analyses. Six pedons were dug and described: two pedons each for maize and oil palm fields, and one each for yam and cassava fields. These pedons were dug to represent sampling units. Auger samples were also purposefully collected from the sampling units at depths 0 -20cm and 20 -40cm. This was to investigate the nutrient spread in the area. Soil samples from the pedogenetic horizons of the pedons were collected after profile description, processed and analyzed. The pedons were designated P01 = cassava field, P02 and P03 = maize fields, P04 = yam field, and P05 and P06 = oil palm fields. The textural classes of the soils included sandy clay loam, sandy loam, sandy clay, loam, clay loam and clay, but the dominant textural class is sandy clay loam. The overall results showed that the soils are acidic; the phosphorus content is generally low; organic matter ranged from 0.42 -4.31 %, decreasing down the profile depth and is medium (>2.0 %) for epipedons. Exchangeable bases are generally low: low exchangeable Ca (<3.2 cmol kg-1), low to medium exchangeable Mg (0.2 -3.2 cmol kg ? 
1-1-1 
), very low exchangeable Na (<0.70 cmol kg) and deficient exchangeable K (<2.0 cmol kg). Total nitrogen content is moderately low to very low (0.042 % < N < 0.196 %). The soils met the criteria for classification as Typic Dystrustults (P01, P03, P04, P05 and P06) and Aquic Argiustults (P02) (Soil Taxonomy), correlated to Acrisols (FAO/UNESCO). The results showed that although climate and topography are optimum or near optimum, there was no current highly suitable (S1) soil unit for maize, cassava and yam cultivation by both parametric and non-parametric methods of suitability evaluation. However, soil units.

CHAPTER ONE

INTRODUCTION 
It is important that the land that will be used for agricultural production should be used according to its capacity for optimization and sustainability of soil productivity (Adeboye, 1994). This becomes very vital at this time when precision farming is gaining wider acceptance and the relevance is particularly more now in the developing world where the use to which a land is put is very often not related to its capacity (Senjobi, 2001). 
A major problem of agricultural development in Nigeria is poor knowledge and appraisal of suitability of parcels of land for agricultural production. The result is poor farm management practices, low yield and an unnecessary high cost of production (Aderonke and Gbadegesin, 2013). Land evaluation using a scientific procedure is essential to assess the potentials and constraints of a given land parcel for agricultural purposes (Rossiter, 1996). The knowledge of soil limitations arising from land evaluation reports aims at ameliorating such limitations before, or during cropping period (Lin et al., 2005). Therefore, soil as a main medium for cultivation needs to be assessed (surveyed / characterized) scientifically. The performance assessment is based on matching qualities of different land units in specific area with the requirements of actual or potential land utilization types. This assessment results in classification of lands as to their suitability to produce specific crops or combination of crops (Ezeaku, 2011). 
Soil suitability evaluation involves characterizing the soils in a given area for specific land use type. The suitability of a given piece of land is its natural ability to support a specified land use such as rain-fed agriculture, livestock production, forestry, etc. The main objective of land evaluation is to predict the inherent capability of a land unit to support a specific land.