1.0 Introduction
Cowpea (Vigna unguiculata) is a leguminious crop with a very vast importance and plays an active role in maintaining the ecosystem, nutrient requirement and the economy of many countries. A considerable amount of cowpea of more than 5.4 million tons are produced in the world annually with Africa producing nearly 5.2 million tons and Nigeria recorded as the greatest producers accounting for about 61% of cowpea production in Africa and 58% of the world cowpea production [IITA, 2009].
According to Wikipedia on Cowpea (2012), and IITA,( 2009); cowpea is one of the most important food legume crop in the semi arid tropics covering Asia, Africa, Southern Europe, and Central America and originated and domesticated in Southern Africa and Asia. [wikipedia/cowpea, 2012. IITA, 2009].
However, some constraint such as agro-ecological constraint, cultivation in marginal and sub marginal land, unpredictable and poor distributed rainfall, lack of soil fertility, seasonal constraint, low productivity, susceptible to pest and disease, flower shedding, tendril formation, lack of adaptive high yielding varieties have been reported to inhibit production of cowpea in some area [Maria et.al,2008].
The practice of shift cultivation to improve soil fertility and enhance production can no longer be sustained due to rapid increase in the world population. Therefore it is necessary to device an improved ways by which the soil fertility can be improved and sustained within the posible shortest time to ensure continual productivity.[ Ayoola et.al 2007]. The use of cover crop such as cowpea have been known to improve the physical , chemical and biological properties of soil.
N:P:K, a mineral fertilizer produced artificially consisting of equal proportion of nitrogen, phosphorous and potassium which are primary macro minerals essential for optimum growth and development of plants. And also used to enhance the productivity of soil.
Poultry manure is an organic manure composed of feacal waste from domesticated birds [poultry] and wood shavings which is added to the soil to enhance the biological , physical and nutrient status of the soil.
Rhizobia are group of bacteria that forms association with the legumes and fix free atmospheric nitrogen to form useable by plants [Ovstyna,2005]. These organisms are usually enhanced by the presence of leguminious plants and organic matter in the soil [FAO, 2005].
Plants obtain nutrient from two natural sources i.e organic matter and inorganic minerals. Organic matter e.g poultry manure release its minerals to the soil through decomposition [FAO,2005]. in the decomposition process, both the soil nutrient and organism present in the soil is increased[Ingham,2000] and according to them, only carefully selected diversified cropping system or well managed mixed crop livestock system are able to maintain a balance in nutrient and organic matter supply and removal.
Changes in land use associated with deforestation and inappropriate land use management has had a negative impact on approximately 2 billion hectares of agricultural land [Pinstrup-Anderson and Pandy Lorch 1998]. Hence, need to improve the soil with organic and inorganic manure to bring about increased productivity. Some other researchers said that land degradation result in the productive decline of soil and can be attributed to changes in the physical, chemical [minerals], and biological attributes from some ideal state brought about by natural or anthropogenic influences [Latham 1994, Lal 1990].
1.2 Objective of the Study
The objective of the study is to verify the effects of poultry manure, N:P:K:15:15;15 and N.P.K/poultry manure combined on growth and production of cowpea as well as on the soil bacteria (rhizobia).
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