Cassava is extensively cultivated as an annual crop in tropical and subtropical regions for its edible starchy tuberous roots, a major source of carbohydrates. It is a shrub with an average height of one meter, and has a palmate leaf formation. Cassava belongs to the family of rubber plants with a white latex flowing out of its wounded stem and leaf stalk. The stem is the planting material from which grows the roots and shoots. Cassava produces bulky storage roots with a heavy concentration of carbohydrates, about 80 percent (Babaleye, 1999). The shoots grow into leaves that constitute good vegetable rich in proteins, vitamins and minerals. New knowledge of the biochemistry of the crop has proved that the proteins embedded in the leaves are equal in quality to the protein in egg (Philip, 1984). Cassava leaves and roots, if properly processed can therefore provide a balanced diet protecting millions of African children against malnutrition. One of the major constraints to increased cassava production in Nigeria is declining soil fertility due to continuous cropping and erosion losses. The use of chemical fertilizers alone to sustain high crop yield has not been quite successful due to enhancement of soil acidity, nutrient leaching, degradation of soil physical condition and organic matter status. Interest in the use of organic manures is increasing day by day. Malcolm (2011) reported that organic manures are fertilizer compound that contain one or more kinds of organic matter. The ingredients may be animal or vegetable matter or a combination of the two. It is possible to purchase commercial brands of organic rich fertilizer as well as prepare organic fertilizer at home by building a compost heap. Animal manure is a common ingredient in the creation of organic fertilizer. Organic manure consists of plants and animal residues at various stages of decomposition. Organic manure is responsible for most desirable surface soil structure, promotes a greater proportion of larger pore size, improves water and air relations and reduces erosion by wind and water. It also improves nutrient status of soils, increases the level of organic matter in the soils and gives high residual effect on soil fertility. Roy et al. (1990) reported that animal manures are excellent soil amendments, but very little is applied to cultivated fields in the tropics and sub-tropics. Although organic matter in most cultivated soil is only 1 – 5% in the top layer of soil (0-25cm) that small amount can modify the soil physical properties. Organic manures are excellent sources of organic matter but relatively low in nutrients; therefore, to obtain optimum yields from continuous cropping, additional nutrients from N.P.K. fertilizers will be needed to compliment organic fertilizer. However, Akoroda (1990) reported that the use of organic manure and N.P.K. fertilizer supplies appreciable cash income to peasant farmers. Since the majority of farmers active in arable crop production in Nigeria are poor, agricultural practices which are cheaper and are more readily available to them should therefore be introduced to them. The response of cassava (Manihot escullenta) to various types of animals manure and N.P.K. fertilizer applied in combinations are not known to have been investigated in Nigeria.
OBJECTIVES OF THE STUDY
1 To access the effectiveness of organic manure and N.P.K. fertilizer on soil properties and shoot dry matter yield of cassava (Manihot escullenta). To establish the optimum rate of combined use of organic manure and N.P.K. fertilizer for cassava production.