Nigeria is blessed with a land mass of about 98 million hectares, out of which 83 million hectares are suitable for cultivation but with only 30 to 34 million hectares presently under cultivation. About 45% of this land area is arable and only about 42% of the arable land is presently cultivated. Nigeria’s population is estimated at about 150 million, making Nigeria the most populous country in Africa and the eighth most populous in the world. Approximately one-third of the population lives in urban areas while rural areas account for the remaining two-third. The climate varies northwards from a humid, semi-hot, equatorial climatic region in the south through wet sub-humid regions and dry sub-humid regions to the semi-arid and arid regions in the north (Abbas, 2009; Aina, 2011). Land cover changes in the last 30 years indicate that disturbed forest increased by about 33%, extensive small holder rain fed agriculture by about 13% and flood plain agriculture by 123%. Forest plantations increased by 58% while rainfed arable crop field increased by 3000% (Aina, 2011). All these suggest intensification in southward movement of the grazing zone in the country. In general, the results presented by Abbas (2009) strongly indicate loss of prime arable lands which is in turn leading to the opening up of new virgin land towards the southern part of the country. In the northern and central parts of the country, the Sudan savanna ecology is transiting to Sahel, an indication that desertification intensity is increasing. In a similar manner, the Guinea savanna in the south is giving way to Sudan savanna grassland. Chronic food insecurity in Nigeria stems from decades of poor governance. In Nigeria, farming has languished and food systems have stagnated leading to mass poverty and endemic starvation among the poor. These conditions have distorted the macro economy with adverse effects on food security as revealed in the statistics of food imports in Nigeria below. As oil prices went up, interest in agriculture waned resulting in grossly inadequate grain per person in all agro ecological zones of the country. It is important to note that the interaction of poverty, hunger and environmental degradation is adversely prominent in Nigeria where the rate of food importation is high under a diminishing low per-capital income (Ekpu, 2009). Recently, soil condition has also been affected by climate change and an increase in the prevalence of severe weather events (that is, drought and flooding) which has brought Nigeria agriculture into crises (Abiodun et al., 2011). In many parts of Nigeria, poor crop yield per hectare of land have been reported with serious concern. This has been attributed to land degradation (Aina, 2011; Lal, 2010). What then is land degradation? Land degradation is a process in which the value of the biophysical environment is negatively affected by a combination of human induced process acting upon the land (Lal, 2010). It leads to a temporary or permanent decline in the productive capacity of the land. Degradation of land includes soil erosion, salinization, nutrient depletion and desertification. The rate of degradation has increased dramatically with growth in the human population and technology. The continued loss of arable land will jeopardize the survival of agriculture (ISRIC/UNEP, 1991). Many past statements on land degradation, and crop yield decline were based on assertions that were largely unsubstantiated by hard evidence. This knowledge gap was the focus of this review.

Description of study area

 

The Nigeria Environment and Land Resources: Nigeria lies roughly between latitudes 4° and 14°N and longitudes 3°and 15°E in West Africa. It covers a land mass of approximately 923,768 km² representing about 14% of land area in West Africa. It is bordered by Benin Republic to the west, the Niger Republic to the north, the sub-equatorial Cameroun to the east and the Atlantic Ocean to the south. The country’s coastline spans over 853 km. A major feature of Nigeria’s coastal and marine environment is the Niger Delta, which covers an area of 70,000 km², and that makes it one of the largest wetlands in the world. The mangrove forests of Nigeria rank as the largest in Africa, the third largest in the world. Nigeria is located mainly within the lowland humid tropics and is characterized by high temperatures almost throughout the year. In the far south, mean maximum temperature is 32°C, while in the north it is 41°C. The mean minimum temperature is 21°C in the south and about 13°C in the north, making the north to have a much higher annual range than the south. The mean annual rainfall over the country varies from a high of over 3,500 mm along the coast to a low of less than 600 mm in the Sahel region in the northwest and northeast parts of the country. The annual variation of rainfall, particularly in the north, is large. This often results in climatic hazards, especially floods and droughts, which bring in their wake much suffering with devastating effects on food production and the nation’s economy (Ogunkunle, 1986; Abiodun et al., 2011).

 

Data collection

           

The data used for this review were collected from Nigeria Federal Ministry of Agriculture, State Ministry of Agriculture, published academic literature, agricultural agencies and books. Information were also obtained from FAO publications on Nigeria.

 

In Nigeria, majority of the farmers are dependent on low external-input agriculture and directly rely on the inherent quality of soil resources which are now been threatened by land degradation. Because of high-intensity (erosive) rainfall susceptible (erodible) soils, and sensitive ecological balances, the process of soil degradation has impacted on yields loss, food insecurity and large food importation bill. Yields were shown to decline because of soil factors, some associated with erosion, which leads to reduction in effective rooting depth; decrease in available water capacity, decline in soil organic carbon and depletion of other soil nutrients. This review suggests that it makes economic sense to address the problems of land degradation through increased conservation investments in land and water resources for sustainable increased food production. 

The authors have not declared any conflict of interest.