Cassava processing produce large amount of waste (cassava peel as the major by-product) and is generally considered to contribute significantly to environmental pollution. In spite of all the important agricultural and nutritional roles played by cassava, its food value and waste (cassava peels) is greatly compromised by the presence of endogenous cyanogenic glycosides; linamarin and lautrstralin which under several prevailing tropical condition is readily hydrolysed to liberate hydrogen cyanide,transferred into a solution and subsequently deteriorate the ground water and crop quality. Hence the need to investigate the effect of cassava peels compost on the macronutrient (nitrogen, phosphorus and potassium) content of agricultural soils on which they are dumped using composting.
After digestion of the soil samples (compost soil and control soil) the concentration of hydrogen cyanide was deduce using titrimetric method, the pH was obtained using pH meter and the macronutrient content (potassium, nitrogen and phosphorus) was obtain using the atomic absorption spectrophotometer, UV spectrophotometer and vanadomolybdo phosphoric method. The analysis result shows that the amendment (cassava peel) used for composting slightly increase the cyanide concentration, potassium content and drastically reduce the major macronutrient(nitrogen and phosphorus) and the pH of the soil thereby making the soil strongly acidic and unhealthy for plant growth. It was observed from the result that the cyanide concentration in the compost soil increase as the rate of decomposition of the cassava peel present in the compost increases. The result obtained; for phosphorus and cyanide a zero order reaction and the rate constant was observe to be 0.012and 0.467 using the method of determination of order and rate constant stated in the literature.
1.1 Background of Study
Cassava (Manihot esculenta crantz) is one of the most important food crops in Africa. It is the third most important food in the tropics after rice and maize. It derives its importance from the fact that its starchy, tuberous roots are a valuable source of cheap calories, especially in developing countries where calories deficiency and malnutrition are widespread (Yeoh et al., 1998); Cassava contains the potentially toxic compounds like the cyanogenic (hydrogen cyanide which is released from damage tissues in any part of plant) glycosides, primarily as linamarin which liberate hydrogen cyanide (HCN) upon hydrolysis and lotaustralin in small quantity. Consumption of cassava and its product is thought to cause cyanide poisoning with symptoms of vomiting, nausea, dizziness, stomach pains, weakness, headaches, diarrhea and occasionally death (Akintonwa and Tunwasha,1994). Cassava processing generates solid and liquid residues that are hazardous in the environment including cassava peels, waste water, cassava leaves etc. Cassava peels which are regarded in many areas in Nigeria as waste are biodegradable waste that is rich in crude protein (5.29%) and fat (1.18%). Most often cassava peels are commonly found in farm locations and processing sites as heaps that are generally perceived as hazard to the environment. These materials, however, could be utilized more effectively and substainably through recycling. Cassava peels like many organic waste material are potential source of organic nutrient to plant . Management of cassava peels include direct incorporation into the soil, feeding them to livestock, burning or processing them into a more stable organic fertilizer called compost (Hoitink,2007). The abundance, as well as low cost of cassava peels in Oleh community has necessitated a research on its effect on agricultural soil on which they are dumped to act as compost. Composting cassava peels eliminate the problem of waste disposal and increase the manurial value of the materials. With the advent of biotechnology approaches, there are opportunities for economic utilization of agro industrial residues such as cassava peels waste (Omisore et al., 2009).
With the advancement of industrial age resulting to take-over of farmlands, there is need to increase and maximize the nutritive life of the available farmland, this can be achievable by humidification of soil instead of adding chemical fertility. In order to convert the increased problem of waste disposal, compositing agricultural-waste to enrich the soil fertility becomes very important. Organic matter are excellent source of plant available nutrient and their addition to the soil could maintain high microbial population activities and as such it is often preferred as alternative to commercial mineral fertilizers. Composting is the decomposition of organic matter such as fruit and vegetables scraps, grass, leaves etc, composting begins the process of breaking down organic material into what will eventually become humus in the soil. Agricultural wastes are essentially of plant origin and therefore contain the entire nutrients essential for plant growth. Plant and animal waste are freely available to be composted to supply nutritious organic matter needed by agricultural soil. Generally, organic fertilizers contain relatively low concentration of the actual plant nutrients, and are not immediately available for plant utilization. Hence, the fortification of organic wastes and their composts as a source of organic nutrients are imperative for sustainable agriculture. According to Neemat and Khaled (2012), traditional composting has been recognised as a low cost and environmentally sound process for treatment of organic wastes (Hoitink and Kuter 1986). Furthermore, the rapid decomposition and raised temperature during composting produced a relatively homogeneous, odor-free, pathogen-free and easy to handle product. Bevacqua and Mellano (1993) reported that the compost treated soils had lower pH and increased levels of organic matter, primary nutrients, and soluble salts.
Primary macronutrients needed by plants are nitrogen, phosphorus and potassium. These nutrients are taken up in large quantities by plants. The primary macronutrients are the most common nutrient deficiencies due to the highest demands by plants. Nearly all soils lack sufficient available nitrogen for ideal plant growth (Cogger, 2005).
1.2 Problem Statement
Cassava processing produces large amount of waste (cassava peel is the major by-product) and is generally considered to contribute significantly to environmental pollution (FAO 2001). A cassava starch production unit processing 100 tons of tubers per day has an output of 45 tons of fresh by-product, which may cause environmental problems when left in the surrounding of processing plants or carelessly disposed (Aro et al., 2010). In Nigeria (Oleh community as a case study) cassava wastes (peels) are usually left to rot away in open (agricultural soil) thereby altering the presence of heavy metal present in the agricultural soil, the pH of the soil and the content of macronutrient available for plant growth or burnt to create space for accumulation of yet more waste heaps thereby resulting in health hazard. The heaps emit carbon dioxide and produce a strong offensive smell (Aro et al., 2010) when burnt.
The main toxic principle which occurs in varying amount in all parts of the cassava plants is a chemical compound called linamerin. It often co- exists with its methyl homologue called methyl- linamarin or lotaustralin. Linamarin is a cyanogenic glycoside which is converted to toxic hydrocyanic acid or prussic acid when it comes into contact with linamarase, an enzyme that is released when the cells of cassava roots are ruptured (Philbrick et al., 1997). However, ingested linamarin can liberate cyanide in the gut during digestion therefore consumption of raw cassava root result in cyanide poisoning with symptoms of vomiting, nausea dizziness, stomach pains, headache and death. Cassava peels which contains large amount of cyanogenicglucosides and pomace (large amounts of biodegradable organic matter) may cause surface water pollution especially if they are stored under heavy rain or simply disposed of in water surface ( Pandey et al., 2000).
1.3 Aim and Objectives of Study
The aim of this study is to analyse the effect of organic wastes (cassava peels) compost generated in Oleh community on the macronutrient (nitrogen, phosphorus and potassium) content and the pH of agricultural soil; experimental and kinetic study. To achieve this aim, the following objectives are considered:
i. Prepare compost using cassava peels from Oleh community;
ii. Analyse the macronutrient content of the compost and the control agricultural soil;
iii. Test the pH of the compost and the control soil;
iv. Analyses the amount of cyanide present in the compost soil and control soil.
v. To determine the kinetics of the macronutrient
1.4 Scope of Study
The scope of the study is to investigate the effect of cassava peels compost on the macro nutrient content and pH of agricultural soil.
1.5 Relevance of Study
Cassava as an important root crop in Africa, widely grown throughout the tropical Africa contain cyanide, generally the cyanide content is substantially higher in the cassava peels. Cyanide is both widely available and easily accessible throughout the world. The compound is not frequently encountered, as it is a potential terrorist agent used as poison and contaminant in the past. Cassava peels may have the ability to cause some certain change in the soil like altering the pH of the soil, improve or reduce the macronutrient content of the soil, alter theheavy metals contents of soil and pollute the water body when dumped on a water surface hence the need to assess the effect of cassava peels compost on the macronutrient content of agricultural soil in Oleh community.