SOIL CHARACTERIZATION AND LAND SUITABILITY EVALUATION OF ANUKA FARMLAND IN NSUKKA LOCAL GOVERNMENT AREA OF ENUGU STATE, NIGERIA

 

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; vthe 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 (1), very low exchangeable Na (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 nonparametric methods of suitability evaluation. However, soil units P01 and P02 showed actual and potential S1 for oil palm production in the study area. None of the sampling units showed high suitability for its current utilization type. The severe constraints to crop cultivation in the area are generally low fertility for all soil units; wetness for soil unit P02 and adverse soil physical characteristic for soil unit P04. Application of organic manure, use of balanced fertilizer and drainage management practices are necessary for maximum productivity of Anuka soils for the evaluated crops.

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.

 

BACKGROUND OF THE STUDY

The pursuit of global food security in the twenty-first century is increasingly dependent on the scientific management of soil resources, which remain the fundamental medium for agricultural production. As population pressures mount, particularly in sub-Saharan Africa, the traditional methods of land use—often based on trial and error or ancestral intuition—are proving insufficient to meet the rising demand for food. In Nigeria, the agricultural sector faces a significant crisis characterized by dwindling yields and accelerated land degradation, largely due to a lack of detailed knowledge regarding the specific capabilities and limitations of the soil. Soil characterization serves as the essential first step in addressing this gap, as it involves the systematic description and laboratory analysis of a soil’s physical, chemical, and mineralogical properties. This “pedological inventory” provides the data necessary to understand how a soil will respond to cultivation, irrigation, and fertilization. When paired with land suitability evaluation—a process of matching the requirements of specific crops with the qualities of the land—it becomes possible to transition from subsistence farming to high-efficiency, sustainable agriculture.

The Nsukka Local Government Area of Enugu State, located within the derived savanna zone of Southeastern Nigeria, presents a unique pedological landscape that demands rigorous scientific investigation. The region is situated on the Udi-Nsukka Plateau, a geographical feature dominated by sedimentary rocks of the Cretaceous age. Specifically, the soils in areas like Anuka are primarily derived from the Ajali Formation, characterized by false-bedded sandstones, and the Nsukka Formation, known for its upper coal measures. These geological origins typically result in soils classified as Ultisols or Alfisols, which are characterized by high acidity, low base saturation, and a tendency toward nutrient leaching. While these soils are often deep and well-drained, providing a good physical environment for root penetration, their chemical fertility is frequently a limiting factor. In the sub-humid tropical climate of Nsukka, high intensity rainfall often leads to the rapid weathering of minerals and the leaching of essential basic cations like calcium, magnesium, and potassium, leaving behind soils rich in iron and aluminum oxides that can fix phosphorus and render it unavailable to plants.

Anuka farmland, as a microcosm of the Nsukka agricultural landscape, represents a critical area for study due to its reliance on crops like cassava, yam, maize, and pigeon pea. For decades, the farmers in this community have practiced continuous cropping with minimal external inputs, leading to a visible decline in soil health and crop performance. The lack of a comprehensive soil characterization for Anuka means that agricultural interventions are often generalized rather than site-specific. Without knowing the exact clay mineralogy, cation exchange capacity (CEC), or organic matter content of these specific plots, fertilizer recommendations remain speculative, often leading to economic waste or environmental harm through soil acidification. Furthermore, the undulating topography of the Nsukka plateau makes these farmlands highly susceptible to sheet and gully erosion. Characterizing the soil structure and hydraulic conductivity is therefore not just a matter of boosting yields, but a necessary step in environmental conservation to prevent the permanent loss of the topsoil.

The application of the Food and Agriculture Organization (FAO) framework for land suitability evaluation in Anuka is essential for categorizing the land into specific classes ranging from highly suitable to unsuitable for various tropical crops. This evaluation considers critical “land qualities” such as moisture availability, nutrient retention, oxygen availability in the root zone, and erosion hazard. By systematically comparing the crop requirements of major staples with the land qualities of Anuka, researchers can identify the “limiting factors” that currently hinder production. For instance, a piece of land might be physically suitable for yam cultivation but chemically unsuitable due to extreme acidity. Recognizing such limitations allows for targeted soil management strategies, such as the application of agricultural lime to neutralize acidity or the use of leguminous cover crops to naturally boost nitrogen levels. This scientific approach ensures that the land is used according to its inherent capacity, thereby preventing the “mining” of soil nutrients and ensuring that the Anuka community can sustain its agricultural heritage for future generations. Ultimately, this study serves as a vital blueprint for localized land-use planning, offering a bridge between traditional farming wisdom and modern pedological science in the quest for regional food self-sufficiency