COMPARATIVE EFFECTIVENESS OF ORGANIC MANURE AND N.P.K FERTILIZER ON SOIL PROPERTIES AND SHOOT DRY MATTER YIELD OF CASSAVA (Manihot esculenta)
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.Organicmanure 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).
2 To establish the optimum rate of combined use of organic manure and N.P.K. fertilizer for cassava production.
2.1 Description and History of Cassava
The cassava root is long and tapered, with a firm homogenous flesh encased in a detachable rind, about 1mm thick, rough and brown on the outside. Commercial varieties can be 5 to 10cm in diameter at the top, and around 15cm to 30cm long. A woody cordon runs along the roots axis. The flesh can be chalk – white or yellowish, cassava roots are very rich in starch, and contain significant amounts of calcium (50mg/100g), phosphorus (40mg/100g) and vitamin C (25mg/100g).However, they are poor in protein and other nutrients. In contrast, cassava leaves are a good source of protein and rich in the amino acidlysine, though deficient in methionine and possibly tryptophan (Phillips, 1984).
According to Stephen (1995), the largest producer of cassava is Brazil, followed by Thailand, Nigeria, Zaireand Indonesia. Production in Africa and Asia continues to increase, while that in Latin America has remained relatively level over the past 30 years. Thailand is the main exporter of cassava with most of it going to Europe. It was carried to Africa by Portuguese traders from the Americas. It is a stable food in many parts of western and central Africa and is found throughout the humid tropics, its cultivation was continued by the colonial Portuguese and Spanish. Forms of the modern domesticated species can be foundgrowing inthe wild in the south of Brazil. While there are several wild manihot species, all varieties of cassava M. esculenta are cultigens.
2.2 Economic Impact of Cassava
Cassava, together with yams (dioscorea species) and sweet potatoes (ipomea batatas) are important source of food in the tropics. The cassava plant gives the highest yield of food energy per cultivated area per day among crop plants, except possibly for sugarcane. Cassava plays a particularly important role in developing countries farming especially in sub- Saharan Africa- because it does well on poor soils and with low rainfall, and because it is a perennial crop that can be harvested as required. Its wide harvesting window allows it to act as a famine reserve and is invaluable in managing labour schedules. It also offers flexibility to resource poor farmers because it serves as either subsistence or a cash crop while underground storage of cassava is advantageous for managing work schedules, it may also lead to reduced quality of the roots, sometimes leaving the root unsuitable for many types of processing. In some areas farmers have to come to increasingly rely on dried cassava chips.
Nweke et al. (1992) revealed that about 42% of harvested cassava roots in west and east Africa are processed into dried chips and flour. No continent depends as much on roots and tuber crops in feeding its population as does Africa. In the humid and sub-humid areas of tropical Africa, cassava is either a primary staple food or a secondary co-staple. In Ghana, for example, cassava and yams occupy an important position in the agricultural economy and contribute about 46% of the agricultural Gross Domestic product (GDP). Cassava accounts for a daily calorie intake of 30% in Ghana and is grown by nearly every farming family. The importance of cassava to many Africans is epitomized in the ewe (a language spoken in Ghana, Togo and Benin Republic) name for the plant, agbeli, meaning “there is life”. However, the price of cassava has risen significantly in the last half decade and lower income people have turned to other carbohydrate rich food, such as rice (Philips, 1984).
In Tamil Nadu, one of the 28 states of India, the national highway 68 between Thalaivasal and Alltur has many cassava processing factories (local name sago factory) alongside it indicating an abundance of it in the neighbourhood. Cassava is widely cultivated and eaten as a staple food in Andhra Pradesh and in Kerela. In the sub-tropic region of southern China, cassava is the fifth largest crop in terms of production, after rice, sweet potato, sugar cane and maize. China is also the largest export market for cassava produced in Vietnam and Thailand. Over 60% of cassava production in China is concentrated in a single province, Guangxi, averaging over seven million tons annually..