ISOLATION AND MOLECULAR CHARACTERIZATION OF INDIGENOUS BRADYRHIZOBIUM SPECIES AND ASSESSING THEIR CAPABILITY TO NODULATE AND FIX NITROGEN IN SOYBEAN (GLYCINE MAX)
CHAPTER ONE
1.0Â Â INTRODUCTION
1.1Â Â Background of the Study
Soybean (Glycine Max [L] Merril) is currently an important cash crop that is widely cultivated in the northern Guinea and Sudan savanna zones of Nigeria (AMREC, 2007). It was first introduced into these agro-climatic zones in 1928 and it has since spread to other parts of the states (Agboola and Moses, 2015). According to Iwe, (2003), Nigeria is the largest producer of soybean in sub-Saharan Africa. Its annual production is estimated by the Ministry of Agriculture to be around 550,000 tons (Abubakar, 2015). Currently, the major soybean producing States in Nigeria are Benue, Kaduna, Taraba, Plateau and Niger, other states include: Delta, Ondo, Oyo, Kwara, and Kogi (Agboola and Moses, 2015). With increased demand for soybean both at home and abroad, this crop is steadily assuming an important position as a source of income for the Nigerian farmers (AMREC, 2007).
One of the major challenges to sustained increase in agricultural production in this part of the country is the low fertility status of most agricultural soils (Machido et al., 2011). Reports in the literature suggest that most of the soils under cultivation for agricultural production in the savannah zone of Nigeria are inherently poor in their content of nitrogen, and available phosphorus (Yakubu et al., 2010; Machido et al., 2011; Laditi et al., 2012). To ensure good growth and economic yield of soybean and other crops, farmers in the region rely heavily on application of inorganic nitrogenous fertilizers and organic manure. But this approach is engulfed with problems such as unavailability and high cost of inorganic nitrogenous fertilizers (AMREC, 2007). Falodun et al. (2010) also reported a significant decrease in soybean yield due to the use of organic fertilizers. This renders the practice unsustainable.
In many countries, the current approach to solving the problems posed by both scarcity of organic manure and high cost of nitrogen fertilizers required for soybean production, relies on the long established understanding that, the soybean crop has the capacity to fix atmospheric N2 in association with soil bacteria belonging to the genus Bradyrhizobium (Peoples et al., 1995). Earlier reports by Peoples et al. (1995) indicates that, soybean crop fixes from 54 to 300kg N/ha while in association with Bradyrhizobium and contributes more than 15kg N/ha to the soil on which soybean is cultivated. This and many other reports (Anuar et al., 1995; Unkovich et al., 1995; Iwe, 2003; Onwualu, 2007; Machido et al., 2011; Abubakar, 2015) tend to suggest that, biological N2-fixation could be the way out for Nigerian soybean farmers where N requirement for soybean production is concerned.
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ISOLATION AND MOLECULAR CHARACTERIZATION OF INDIGENOUS BRADYRHIZOBIUM SPECIES AND ASSESSING THEIR CAPABILITY TO NODULATE AND FIX NITROGEN IN SOYBEAN (GLYCINE MAX)
