RESPONSE OF GROUNDNUT (Arachis hypogaea L.) TO RHIZOBIA INOCULATION, NITROGEN AND PHOSPHORUS FERTILIZERS ON AN ALFISOL IN THE NORTHERN GUINEA SAVANNA OF NIGERIA

CHAPTER ONE
1.0 INTRODUCTION
1.1 Background
Groundnuts (Arachis hypogaea L) also known as peanuts, is a leguminous crop, a member of the genus Arachis in the family Leguminosae. It is widely grown in the tropics and subtropics due to its nutritional and economic importance. Groundnut is the most widely grown major legume worldwide cultivated in 118 countries and occupies more than 22.6 million ha that produce about 36.4 million MT, with average yield of about 1600 kg ha-1(Abate et al., 2012). Groundnut seeds (kernels) contain 40 -50 % fat, 20 – 50 % protein and 10 – 20 % carbohydrates (ICRISAT, 2003). Groundnut seeds are nutritional source of vitamin E, niacin, calcium, phosphorus, magnesium, zinc, iron, ribloflavin, thiamine and potassium (Kumar and Shankar, 2013). In most of the developing countries it provides high-quality cooking oil and is an important source of protein for both human and animal diet and also provides much needed foreign exchange by exporting the kernels and cake. The uses of groundnut plant therefore, make it an excellent cash crop for domestic markets as well as for foreign trade in several developing and developed countries (FAO, 2002). In Africa, groundnut is grown mainly in Nigeria, Sudan, Senegal, Chad, Ghana, Congo, and Niger. Average productivity is 1720 kg ha-1 in Nigeria which is poor when compared to the USA and other developed countries where it is close to 3500 kg ha -1 (Vara-Prasad et al., 2009). The crop is grown mostly by smallholder farmers under rainfed conditions with limited inputs (Samson, 2012).

Majority of the soils of the Guinea savanna of Nigeria are inherently low in fertility especially organic matter, phosphorus and nitrogen (Odunze and Kureh, 2009; Oluwasemire and Alabi, 2004). To address this challenge, farmers in the northern Guinea savanna use  strategies such as application of organic and inorganic fertilizers (Samson, 2012). The use of inorganic fertilizers is effective but costly (Obisesan et al., 2013); this therefore, leads to application at sub- optimal level that is, below the recommended rate (Olawale et al., 2009). On the other hand, organic fertilizers, such as crop residues and animal manures are bulky. They contain relatively low concentration of nutrients and handling them is laborious. ICRISAT (1995) recommended an application of 10 -12 t ha-1of chicken manure or 20 t ha-1 of well decomposed farm yard- manure for groundnut production. Wamba et al. (2012) gave the nutrient content of poultry manure as 21.76 N g kg-1, 8.74 P g kg-1 and 11.22 K g kg-1. This however depends on the handling conditions. Much of the N in manure may be lost to the air if they are allowed to dry out or stored for a long time.