CHAPTER ONE

INTRODUCTION

1. 1      Background of the Study

Soil is one of the world‘s greatest resource. It has been described as a natural body of animal, mineral and organic constituents, differentiated into horizons of variable depth which differ in morphology and physical, chemical and biological characteristics (Joffe, 1948). It is an important natural resource that either directly or indirectly supports most of the planet's life. A major function of soil on man is that it supports food supply and food security. Soils affect food security directly because it supports agriculture. Agriculture produces the food we eat and provides the primary source of livelihood for 36% of the world‘s total workforce (ILO, 2007). Therefore, threat to soil is threat to food security and economies which rely on agriculture. Food security is directly linked to the ability of the land to support populations (Scherr and Yadav, 1996).

Global concern about soil degradation has grown because of its threat to agriculture and food security. Low agricultural production, food insecurity, low income of the rural population and poverty are consequences of soil degradation (Junge, Deji, Abaidoo, Chikoye and Stahr, 2008). Agcaoili, Perez and Rosegrant (1995) estimated that increasing degradation would lead to as much as 10% decline in productivity in the developing countries and could lead to worsening malnutrition in the developing world.

Some of the challenges posed by soil degradation to food security in the developing countries are; long-term investment and appropriate technology development, dampened economic growth effects of lower farm incomes in irrigated, high quality rain fed and densely populated marginal lands due to lost soil productivity and threat to nutrition and deaths from malnutrition and diseases associated with poor diets (Eswaran, Almaraz, Van den Berg and Reich, 1997; Swift and Shepherd, 2007).

Soil degradation is a loss of soil function. It is a serious and most common form of land degradation because the soil is the basis for production (Blum, 1998). It encompasses physical, chemical and biological deterioration. Examples of soil degradation are loss of organic matter, decline in soil fertility, decline in structural condition, erosion, adverse changes in salinity, acidity or alkalinity, and the effects of toxic chemicals, pollutants or excessive flooding. Soil degradation is the decline in soil quality caused by its improper use, usually for agricultural, pastoral, industrial or urban purposes. A soil is said to be degraded if the loss of basic qualities which manifest in reduced yields, is permanent (Mbagwu, 2003). Soil degradation occurs globally but its negative impacts are most felt in regions which depend solely on agriculture for its income (Swift and Shepherd, 2007). Increased pressure on land as a result of increasing world population has led to increased degradation of world soils. Soil degradation may be exacerbated by climate change.

Soil erosion by water is the commonest way in which soils are degraded and many forms of soil loss are most easily seen during or shortly after periods of heavy rains (Stocking and Murnaghan, 2000). Soil erosion associated with poor land use and management practices is one of the main factors causing degradation (Gessess, Klik and Hurni, 2009). Bridges and Van Baren (1997) observed that the presence of erosion is an indication of an underlying problem. They observed that though soil erosion is a cause and effect of soil degradation, it is easier to treat the cause than the effect. Any negative change in soil properties may lead to decline in soil quality and its ability to resist degradation. Soil degradation processes can occur without human interference but accelerated rates of degradation are often influenced by man‘s intervention in natural processes. Over grazing, over cultivation, water logging and deforestation are some of the main causes of soil degradation. Soil degradation is defined by reference to productivity. Studies show that farmers‘perception of declining soil quality are tied to agricultural productivity (Bridges and Van Baren, 1997). Studies also show that soil erosion reduces soil quality (Barrow, 1991; Sanchez, Recalata, Antolin, Carbo‘ and Depaz, 2004). Doran and Parkin (1994) define soil quality as the capacity of a soil to function within ecosystem boundaries to sustain biological productivity, maintain environmental health and promote plant and animal health. Sensitivity and resilience are measures of the vulnerability of soils (Doran and Parkin, 1994; Stocking and Murnaghan, 2000). This vulnerability is affected by factors such as topography, soil properties and human influence (Stocking and Murnaghan, 2000). Soil resilience is defined as the ability of a soil to restore its living systems after disturbance while sensitivity is the degree to which a soil undergoes change due to natural forces, human intervention or a combination of both (Bridges and Van Baren,1997; Stocking and Murnaghan, 2000).

Soil compaction is a major form of soil degradation. It is estimated that soil compaction has resulted in reduction of yields by 20% to 50% in Europe and North America and 40% to 90% in West Africa (Oldeman, Hakkeling and Somboek,1991). Nutrient depletion is another form of soil degradation with serious economic implications for many regions of the world. Experts estimate that soil erosion in Zimbabwe result in an annual loss of P and N (totaling $1.5 billion), while in Asia annual economic loss is estimated at $600 million. In Nigeria, Lal (1995) observed dramatic reductions in maize yields ranging between 30-100% after simulating the effects of soil erosion by artificially removing topsoil on plots. In the same study, yields of cassava also reduced by 14-31% and observations showed that fertilizer amendments did not appear capable of restoring the yields where 10-20cm of top soil had been removed. Egboka and Okpoko (1984) observed that though the development of gullies in Angulu-Nanka region of Anambra state had been attributed to the influence of human activities on geomorphological processes, observations also showed that the hydrogeological and geotechnical properties of the complex aquifer system underlying the affected areas were also responsible for the degradation of soils in the region. Similarly, Junge (2010) observed that land use intensification led to increased soil erosion and depletion of soil organic matter and nutrients which invariably led to decrease in arable and grazing land, crop production, diary produce and dwindling income for local farmers. Some implications of land scarcity include rural-urban migration, conflicts between land users over scarce productive lands, food insecurity and poverty.

1.2       Statement of the Problem

Due to rapid population growth, land use is being intensified the world over with severe consequences on land resources. In Nigeria where the population dramatically rose from 116million in 1991 to 140million in 2006 (Federal Republic of Nigeria, 2007) human-induced soil degradation has intensified, due mainly to expansion of agricultural lands into marginal areas. In the developing countries, such as Nigeria, poor rural households are often found in the marginal agricultural lands where land productivity and income are stagnant or declining. There is, however, very limited data on the processes and impact of soil degradation in many regions of the world especially in Africa where many economies and livelihood depend on agriculture.

In Benue, various studies have been carried out to assess soil degradation. Kowal (1970) used experimental plots to assess soil loss in a sub basin in Samaru. Odunze (2002) estimated the magnitude and timing of soil loss from cultivated lands under mulch conditions and observed that soil erosion is most prominent in cultivated areas during the early part of the rain-fed crop production season when most soils are bare. Similarly, Yusuf (2006) in his study of the magnitude of suspended sediment production by a tributary of the Kubanni river (in Kaduna State), observed that poor conservation and land use practices were responsible for extensive rilling and gullying of the Kubanni river in the Zaria area. However, Iguisi (1996) in his study of variations of soil loss in two sub-basins in Zaria, observed that results obtained from the use of experimental plots in assessing soil loss was not representative of the entire basin and could not be used to assess soil loss in the basin.

One other major weakness of estimating soil loss from a field is that the estimates of soil removed from fields are subject to uncertainties about where and when the sediments are derived (Stringer and Reed, 2006). The universal soil loss equation often predicts soil moved on to a field but not from a field and may over state the amount of soil lost to productivity. Stringer and Reed (2006) in assessing land degradation in South Africa, pointed out that using scientific methods such as remote sensing and GIS in measurements of soil properties have limitations. They observed that satellite imageries may guide the sampling of fields but are often not as effective as on-field erosion assessment. Thus, while a number of studies on soil degradation have been carried out in Benue, most of such studies are centred on use of experimental plots. Consequently, such studies are not representative of the entire basin. Furthermore, none of these studies have looked at the problem of degradation from the land users point of view. Similarly, the dynamics and extent of soil degradation are changing with time and there is need for participatory approach to soil degradation assessment and providing a holistic and up to date picture of the problem. Few attempts have been made to assess the extent and severity of soil degradation in the study area and tackle the problem at a broader scale. These are the gaps that the study intends to fill.

1.3       Objectives of the Study

This study aimed at an assessment of soil degradation in the Makurdi, Benue State. This was achieved through the following set of objectives:

1.         Identifying the land use and land cover change patterns of the area using satellite imageries for three periods.

2.         Identifying the forms of soil degradation in the study area.

3.         Determination of key soil physico-chemical indicators of soil degradation over major land uses in the area.

4.         Assessment of farmers‘awareness of the causes and consequences of soil degradation as well as attitude towards land management practices.

1.4       Research Questions

A careful observation of the landscape of the study area raises the following research questions:

1.         What are the implications of changing landuse/cover for soil degradation?

2.         What are the forms of soil degradation in the study area?

3.         What are the indicators farmers use to assess soil degradation on their farms?

4.         What are the coping strategies of farmers in response to soil degradation?

1.5       Research Hypotheses

Deriving from the objectives of the study are the following hypotheses:

1.         There has not been any significant change in land use/land cover in Makurdi Benue State in the past 20 years.

2.         There are no significant variations in the severity of soil degradation in Makurdi Benue State.

3.         There are no significant relationships between farmers‘socio-demographic characteristics and coping strategies adopted by farmers in response to soil degradation in Makurdi Benue State.

1.5       Significance of Study

The need to understand the dynamics of soil degradation in terms of extent and severity cannot be overemphasized. Knowledge about the dynamics of soil degradation is important in the sustainable use and management of soil resource. Soil resource is essentially non-renewable. Therefore, avoidance of soil loss by improved management and conservation of the natural resources through sustainable use of land resources is important in combating low agricultural production, food insecurity and its associated negative effects on poverty levels and population drift (Tekwa, Belel and Alhassan, 2010).

The challenge of African agriculture is not only to enhance food production to meet the growing needs of its expanding population, but also to maintain the productive capacities of soils into the future. Although land use intensification can increase food production in the ‗high potential‘ areas (Barbier, 1997) evidence also shows that the extension of agricultural activities into marginal lands have tremendous negative effects on the quality of soils (Abubakar,1995; Sherr and Yadav, 1996). Rehabilitation of degraded lands must be comprehensive and in line with the principle of sustainable development. A good way of tackling the menace of soil degradation in Africa in general and Nigeria in particular, is to provide adequate, accurate and relevant information on the forms, extent and severity of soil degradation. This can be achieved by incorporating farmers‘knowledge and perceptions of soil degradation phenomena into science based methods (quantification and analysis) of soil degradation assessment. This will provide a realistic and holistic means of assessing soil degradation while taking full advantage of the farmers‘ experience and dynamic knowledge of their environment (Vigiak, Okoba, Sterk, and Stroosnijder, 2005; Stringer and Reed, 2006).

1.6       Scope of the Study

The scope of the study is Makurdi, Benue State. The study entailed the use of remote sensing and GIS for the establishment of changing pattern of land degradation and other land uses. This was followed by field assessment of the nature and severity of soil degradation and physico– chemical status of the soils. The farmers’ perception of soil degradation problem and coping strategies was sought through the use of structured questionnaires and focus group discussions. In assessing the physico-chemical indicators of soil degradation only the surface horizons of soils were considered. Similarly, the soil properties that were considered are those that are key to degradation process, including particle size distribution, bulk density, porosity, moisture content, organic matter content, exchangeable cations, CEC and pH.

1.7       Definition of Terms

Soil Degradation: is the decline in soil condition caused by its improper use or poor management, usually for agricultural, industrial or urban purposes. It is a serious environmental problem. Avoiding soil degradation is crucial to our well-being. Soil degradation simply means the decline in soil quality which comes about due to aspects such as improper land use, agriculture, and pasture, urban or industrial purposes. It involves the decline of the soil's physical, biological and chemical state.

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