EFFECT OF 3 ORGANIC MANURE TYPES ON GROWTH OF Vigna unguiculata L
1.1 Background of the Study
The problem of declining soil fertility in crop-based farming system of sub-sahara Africa is well known (Nwajiuba and Akinsanmi, 2002). The use of organic amendments in agriculture has increased over the years due to the increasing cost of inorganic (chemical) fertilizers and high demand for quality and uncontaminated products (Sangkkara, 1993). The value of organic amendments in crop production is centered on the ability of animals and plants to provide nutrients and to improve the chemical, physical and biological properties of soils (Ifia, 1992). The regular addition of organic amendments to soil is very important in the developing world of the tropics, where most traditional farming systems are not sustainable (Sangakkara, 1993). Organic manure improves soil tilth, infiltration rate and soil water holding capacity, contributions nutrient to the crop and it is an important organic matter (Bill, 2001). The particular significance of organic manure for soil fertility is that it influences so many different soil properties (Ifia, 1992). Maynard (1991) reported that in many parts of the tropics most annual crops respond well to application of organic manure. Organic manure enhances soil water holding capacity and reduces bulk density (Sangakkara, 1997). The beneficial effect of organic matter on crop productivity is a function of so many factors, which include greater vigor of plant, improvement of soil properties and greater uptake of nutrients (Higa, 1994). Like many other legumes, cowpeas can symbiose with nodule bacteria (Rhizobia) present in most, if not all tropical soil. The Rhizobia posses the nitrogenase complex, an enzyme capable of reducing atmospheric Nitrogen into compounds assimilable by the host plant (Mulongoy, 1985). Legumes need a high phosphorous requirement for nodule development and optimal growth and nodulation in Cowpea. Generally, Cowpea reduces in acid aluminum rich soils where even tolerant strains fail to root hairs (Applebaum, 1990). Factors such as manganese toxicity may also be involved in reducing cowpea nodulation at low pH (Applebaum, 1990). The general small amount of literature on the effect of organic manure on the modulation of cowpea encouraged this investigation aimed at identifying the possible effect of organic manure on soil chemical properties and nodulation of cowpea varieties in the Southeastern part of Nigeria where cowpea production is still on the marginal level.