EFFECT OF LONG TERM ROTATION, NITROGEN FERTILIZER AND TILLAGE ON SOIL QUALITY AND MAIZE YIELD IN THE NORTHERN GUINEA SAVANNA OF NIGERIA

CHAPTER ONE

        Introduction

Long-term field experiments are expected to provide important information regarding soil properties as affected by cropping system and soil management practices. Legumes such as cowpea and soybean add both organic matter and nitrogen (N) to the soil (Omay et al., 1997; Sainju et al., 2003) and increase soil fertility. Maize is the second most essential cereal crop after sorghum in sub-Saharan Africa; it is grown much more intensively than it was estimated since 1985 (FAO, 1999). In Nigeria, maize yield averages about 1.4 tons per hectare and this is only about 20% of the average in Canada and other parts of the world where intensive cereal production is carried out (Afolami and Fawole, 1991; FAO, 1999). Studies have shown that legume-cereal rotation produce relatively higher grain yields than either crop grown alone (Rao and Mathuva, 2000; Olufemi et al., 2001; Mpairwe et al., 2002; Dapaah et al., 2003). Rotating maize with grain legumes is often targeted towards utilizing biologically fixed-nitrogen by legumes for the benefit of the maize (Yusuf et al., 2009). Nitrogen fertilizers are most effectively used as part of a balanced fertilization plan that aims to maximize economic return of a cereal–legume rotation system; Nitrogen fertilizer, apart from increasing the content of nitrate in soil that leads to its leaching (Porter et al., 1996), results in changes in soil pH and many other soil properties (Brady and Weil, 2002). Long-term field experiments with N fertilization can give valuable information about how those changes occur and indicate the trends of the changes (Dragan et al., 2010). Nitrogen (N) is most often the yield limiting nutrient with respect to crop production (Factsheet, 2014). Nitrogen contributes firstly to grain yield and forage biomass production, and at the same time to protein (Eche, 2011). Nitrogen is essential for seed formation and maturity. A steady supply is needed during the early growth stage and this steady supply can be provided by the action of soil microorganisms on the soil organic matter (SOM) or by application of inorganic fertilizers (Eche, 2011).