CHAPTER ONE
INTRODUCTION
Maize (Zea mays L.) is an important staple food crop and
provides bulk of raw materials for the livestock and many agro-allied
industries in the world (Bello et al, 2010; Randjelovic et al, 2011). It is the
third most important grain crop in the world after wheat and rice (USDA and FAS
Grain, “Zea production maps and statistics,” 2010). Maize is of significant
importance for developing countries like Nigeria, where rapid increase in
population have already out stripped the available food supplies in which maize
serve to ameliorate due to its high productivity and diversified use. More
maize is produced annually than any other grain (IITA 2006).
Worldwide production of maize is 785 million tons, with the
largest producer, the United States, producing 42%. Africa produces 6.5% and
the largest African producer is Nigeria with nearly 8 million tons, followed by
South Africa. Africa imports 28% of the required maize from countries outside
the continent (IITA 2006). 158 million hectares of maize are harvested
worldwide. Africa harvests 29 million hectares, with Nigeria, the largest
producer in Sub Sahara Africa (SSA) harvesting 3%, followed by Tanzania (FAO,
2007). Worldwide consumption of maize is more than 116 million tons, with
Africa consuming 30% and SSA 21%.
The tropical rainforest agro-ecology of Nigeria has a great
potential for its production because of its high solar radiation coupled with
much precipitation that favours maize production. In the southern rainforest
belt of Nigeria, maize is grown twice due to bimodal rainfall pattern (a short
early growing season followed by fairly long late season). Early maize
varieties are usually planted at the onset of rainy season before it’s fully
established (March/April), and matured sooner than the traditional crops. This
succours in filling the hunger gap in July when all food reserves have been
depleted after the long dry period in the zone. On the other hand, the late
season crop is planted during the second cycle of rains (July/August). While the
short early season is usually characterised by abrupt cessation of rains during
crop cycle, the late season is normally affected by terminal drought. The
occurrence of extreme environmental events impose different degrees of drought
stresses on maize thereby affecting growth duration, plant size, dry matter
accumulations, assimilate reserves and grain yield .
Efforts aimed at obtaining high yield of maize would
necessitate the augmentation of the nutrient status of the soil to meet the
crop’s requirements for optimum productivity and maintain soil fertility.
In spite of the increase in land areas under maize
production, yield is still low. Some of the major causes of low maize yield are
declining soil fertility and insufficient use of fertilizers resulting in
severe nutrient depletion of soils (Buresh et al, 1997). Maize requires
adequate supply of nutrients particularly nitrogen, phosphorus and potassium
for good growth and high yield. Evaluation of early (90-95 days)and late
(100-105 days) maturing maize have formed part of the varietal trials in the
marginal environments of the region under the auspices of International
Institute of Tropical Agriculture (IITA) Ibadan, Nigeria (Badu-Apraku et al,
2003; Sallah et al, 2004; Olaoye and Omueti,2006; Oluwaranti et al, 2008). Base
on maize Investigations carried out, the crop has been observed to produce well
under high soil fertility condition (Yusuf and Iwuafor, 2005). The nutrient
supply to each crop is observed to be influenced by fertilizer supply to previous
crop (Negassa et al, 2001; FAO, 2006; Rutunaa and Neel, 2006). Notwithstanding,
the yield of maize varies among varieties, planting site coupled with
availability of integral factors such as soil nutrient status and fertilizer
application. Nitrogen is a vital plant nutrient and a major yield-determining
factor required for maize production (Adediran and Banjoko, 1995; Shanti et al,
1997). Low N availability has limited cereal crop growth more than deficiencies
in any other minerals (Carsky and Iwuafor, 1999). Thus maize yield has been
dangerously reduced especially in developing countries of the world where maize
production is carried out under low soil fertility condition (McCown et al,
1992; Oikeh and Horst, 2001).
It was in view of the above that this study was conducted to
evaluate the performance of early and late maize varieties under varying times
of applied fertilizer following a bush fallow. The following objectives where
conceived:
(1). Evaluate the growth and yield of early and late
varieties of maize in tropical rainforest environment.
(2). Determining the appropriate time of fertilizer
application that would support optimal growth, yield and development of early
and late maturing maize varieties.