Soil fertility decline is one of the acute problems facing farmers in the world and Nigeria in particular. The constraints to food security and widespread poverty, as they affect development and livelihoods, are well known even in Sub-Saharan region of Africa (SSA), where population growth at 3% supersedes agricultural production rate of 2% per annum (Bationo et. al, 2006). Although the causes of food insecurity and poverty are numerous, the decline in soil fertility with resultant decreasing crop yields is severally highlighted and stressed (Sanchez et. al, 1997; Smaling et. al, 1997; Bationo et. al, 2006).
In Nigeria, the practice of shifting cultivation which was one of the effective methods of overcoming the problem of poor crop yield due to decline in soil fertility has virtually disappeared. This could be linked to the increasing population explosion and the stiff competition for land space by other land uses (Hati et. al, 2005). According to Ayoub (1994), population explosion added to the increased continuous farming on the available land by farmers who often do not add adequate soil nutrient supplements (organic and inorganic fertilizers) to beef up soil fertility and increase yield.
Makinde et. al, (2001) reviewed that decline in soil fertility is a fundamental impediment to agricultural growth and food production. According to them, crop production in the past relied on shifting cultivation to maintain the fertility and productivity of the soil through organic matter build up during a long fallow period. This practice enabled farmers to produce substantial crop yield over a period even without adding external inputs. Okalebo et. al, (2009) observed that decreases in available nitrogen and phosphorous are among the most severe nutrient problems in the tropics.
To cope with these problems, there has been an increase in the use of inorganic fertilizer mostly ammonium sulphate ((NH4)2SO4) fertilizer. The continuous use of the mineral fertilizers resulted to increase in acidity of such soils. Researchers have shown that pH decline occurs more rapidly in continuously cropped lands and soils tend to acidify over time particularly when large application of ammonium-based fertilizers and urea-based fertilizers, [Co(NH2)2] are used.
Soil acidity is a major problem in crop production in the tropics. This is especially so in more than 90% of soils in the agroecological zones in Nigeria (Enwezor et. al, 1990). The problems of soil acidity are very prevalent in southeastern Nigeria where coarse sedimentary parent materials had undergone earlier cycles of weathering before deposition (FDALR, 1990).