Yield and Storability of Sweetpotato (Ipomoea Batatas (L.) Lam) as Influenced by Chicken Manure and Inorganic Fertilizer


Two field experiments were conducted at the Multipurpose Crop Nursery of the University of Education, Winneba, Mampong-Ashanti campus during the minor and major rainy seasons from September, 2011 to January, 2012 and April to August, 2012 respectively to verify the yield and storability of sweetpotato roots as influenced by chicken manure and inorganic fertilzer in the forest transitional agro-ecological zone of Ghana.. In both cropping seasons sweetpotato root tubers were stored for three (3) months after each harvest using three storage methods (Pit, Ash and Grass). The experimental design used for the field experiment was a 2 x 8 factorial arranged in randomized complete block design with four replicates in both studies. In the storability studies the experimental design used was a randomized complete block design with three replications. Sixteen (16) treatments were included in the field experiments. The factors under field study were two varieties of sweetpotato (i) Apomuden (Deep orange-fleshed colour with light orange skin), (ii) Okumkom (White-fleshed colour with light purple skin) and chicken manure and inorganic fertilizer (NPK) combination consisting of seven (7) organic manure and inorganic fertilizer rates and the control. In the storability studies the harvested tubers from the eight field treatments were sorted, cured and stored using the three storage methods (Grass, Ash and Pit). The results obtained revealed that the application of a combination of organic manure (chicken manure) and inorganic fertilizer for soil fertility enhancement in sweetpotato production is a better option than either organic or inorganic fertilizer applied alone. Apomuden grown on 15 – 30 – 30 kg/ha NPK + 5t/ha CM had the highest marketable and total tuber yield during the major cropping season, while Okumkom grown on 15-23-23 kg/ha NPK + 5t/ha CM and other amendments had the highest vegetative biomass (number of leaves per plant and vine fresh weight at harvest) in both seasons. Correlation analyses for both seasons showed that the vegetative growth was negatively


correlated with tuber yield and market quality. However, tuber market quality was highly positively correlated with total yield of tuber. The vegetative characters were positively and significantly correlated with each other. The importance of using chicken manure and inorganic fertilizer either alone or preferably in combination as soil amendment to enhance tuber market quality at harvest, tuber nutritional composition with regard to beta-carotene, starch and sugar content over the control was clearly shown from both studies. The sweetpotato root tubers of both varieties with regard to beta- carotene, starch and sugar contents increased with manure application, especially, during the minor season. The results from both seasons clearly showed that for both varieties the pit method was the most effective storage method in terms of beta- carotene as well as starch and sugar contents over both ash and grass storage. Pit storage of Apomuden and Okumkom grown on amended and control plots resulted in improved beta-carotene, starch and sugar contents of root tuber and also stored better than ash and grass storage systems in both seasons. With regard to the cost benefit analysis Apomuden and Okumkom grown on 30-30-30 kg/ha NPK treatment dominated the other amended plots and the control in both growing seasons.


1.0            INTRODUCTION

1.1      Background of Study


Sweetpotato (Ipomoea batatas (L.) Lam) is a dicotyledonous plant belonging to the family Convolvulaceae. It is an important tuber crop grown in the tropics, sub-tropics and warm temperate regions of the world. The crop has a short duration (3 – 4 months).

Sweetpotato is the world’s seventh most important staple crop, grown in over 100 countries of the world, covering an estimated total area of 9.2 million hectare, with an annual global production around 125 million tonnes. Almost 95% of the total production is in developing countries. Being relatively resistant to pests and diseases and comparatively water-use efficient, sweetpotato grows well in regions of marginal agricultural production. The crop has the additional advantage that due to rapid soil coverage and good rooting characteristics, it helps to reduce soil erosion. Thus, sweetpotato is a particularly valuable crop for poorer farmers. This is reflected in the distribution of the crop. With an annual per capita production in Africa averaging nearly 9 kg per capita consumption often exceeds 100 kg within poorer communities (CIP 1996).


In many parts of Africa, including Ghana, the crop is grown for its staple properties. The root tuber is eaten boiled or as fried chips. It is also prepared into flour for various domestic uses and drinking juice can also be extracted from the root tuber (CRI, 2003). As a fast growing root crop that can be grown in all regions of the country, giving yields of 20


to 25 tonnes per hectare within four months, Sweetpotato has become an important food crop in Ghana. It is also gaining importance as an export crop in the Bawku East District of the Upper East Region. Farmers in the district export the crop to Burkina Faso, where good prices are obtained (CRI, 2003).


1.2      Problem Statement /Justification


The production of sweetpotato is particularly in the Northern and Central Regions of Ghana and as such local producers are not able to meet the demand for this crop in the country. Although the Crop Research Institute (CRI) in Kumasi had released improved varieties of sweetpotatoes with white, yellow and orange – flesh colours to farmers, it has been observed that the few Ghanaian farmers who engage in small scale potato cultivation in some selected areas in the country face a myriad of problems. The major problem is that there have not been extensive studies on the crop to equip farmers with adequate information on the agronomic practices. Rather work on testing adaptability and acceptability of these released varieties through farmer participatory research and dissemination of planting materials has been carried out (CRI- CSIR, 2006).

Despite its many benefits, sweetpotato is characterized by a low production, yield and tuber quality in the country. This can be attributed to among other factors, the low fertility of the soils on which the crop is grown. Sweetpotato responds to phosphorus and potassium application under most conditions though the response rate and hence optimum dose varies with the cultivar and soil types. Soil fertility depletion in smallholder farms is currently recognized as the fundamental biophysical cause of declining per capita food production in Africa. The inherent poor soil fertility of most soils in the tropics and


subtropics constitute a major constraint in sustainable smallholder crop production in Sub- Saharan Africa (Myers et. al. 1994; Smailing et al., 1997).


The use of both organic and mineral fertilizers is often limited and this has resulted in a gradual depletion of soil nutrients in sub- Saharan Africa (Smailing et al., 1997). Increase in population which has resulted in land shortages has led to reduction in traditional methods of maintaining soil fertility. Technologies based on combinations of organic and inorganic sources of fertilizer would produce higher and more sustainable yields than either organic or inorganic fertilizer alone (Mukhtar et al., 2010).

The soil in the production areas are characterized by low nitrogen, phosphorus and potassium levels (SRI-CSIR, 2003). Since there is increased focus on sweetpotato as source of energy and nutrients to meet the caloric and nutritional needs of the rapidly growing population in Ghana, there is therefore the need to improve the fertility of the soil through good management of potassium and phosphorus to achieve increase tuber yields.



Chemical fertilizers have been the conventional way supplying nutrients to the crop. However with the increasing cost of fertilizers following the removal of government subsidy on the commodity, farmers are looking for alternative but sustainable methods of cultivating the crop. Applying poultry manure in combination with inorganic fertilizers provides a favourable condition for both high and stable yields of various varieties of crops (Palm et al., 1997).


In Ghana, not much work has been done on fertilizer regimes for optimum growth, yield and development of sweetpotato. There is therefore the need for intensive research work on nutrient supply to optimize the yield potential of the crop for commercial and industrial


utilization. The identification and selection of appropriate combination and rates of inorganic and organic fertilizers will increase the production levels of sweetpotato in the country and offer the possibility of utilizing the tubers in production of composite flours thereby reducing the importationlevel of wheat flour and similar products for the food industry in Ghana.

The use of foods rich in vitamin A to combat vitamin A deficiencies is gaining importance in most parts of Africa. Increasing the consumption of the foods rich in vitamin A is considered one of the food-based strategies for addressing vitamin A deficiency in the communities (Smailing et al., 1997).

There is the need to satisfy different sectors of the society and to provide the vital nutrients in the diet of those suffering from numerous ailments. There is therefore the need to provide an alternate (cheap) source of these elements. In view of these the inclusion of the orange fleshed cultivar which is important for vitamins and the white fleshed cultivar which is also important source of energy in the evaluation is appropriate in optimizing the soil nutrient supply for different sweetpotato types grown in the country to help combat malnutrition among the under resourced.


There are adaptable varieties that are suitable for the local climatic conditions and planting materials have been released to farmers by Crop Research Institute in the country. Additionally, high beta- carotene cultivars have significant role to play in the national crusade against Vitamin A deficiency (CRI, 2004).


Another serious constraint in large scale production and utilization of sweetpotato in Ghana is the short shelf life of the harvested tuber.The crop is highly perishable and as such requires good storage technique. Lack of suitable storage facilities among smallholder


farmers continues to expose farmers to intermittent food shocks even after harvesting of the crop. Farmers rely on preservation methods derived from indigenous knowledge systems for storing the harvested sweetpotato tubers.Studies indicate that post harvest losses due to pest and diseases attack can account for as much as 40-60% of crop output (Amoah et al., 2010). Important techniques of preserving crops derived from indigenous knowledge have rarely been subjected to scientific enquiry. This study is premised on the observation that local smallholder farmers in Ghana use most preservation methods informally but not much is known about their efficacy from a scientific perspective. This study will also examine the different sweetpotato storage techniques to compare their efficacies and comparative effects on tuber quality. Information gleaned from these studies may help to fine tune the indigenous technologies and popularize their use for improvement in sweetpotato production and preservation. This will stem the current trend of abandoning indigenous knowledge systems for more expensive and sometimes hazardous chemical- based methods.

The principal post harvest problems associated with sweetpotato storage are fungal rots, weevil damage and physiological changes (IITA, 1996). The only available storage methods for sweetpotatoes are by leaving the crop in the ground and harvesting it only when needed and trench storage (FAO, 1991). Eka (1998) reported that there is also dearth of information on nutrient changes during storage of most root and tuber crops in Nigeria. It is therefore important to optimize nutrient supply for high yield in the commonly cultivated sweetpotato types in Ghana and to carry out a systematic study of the effects of some storage methods on the stored sweetpotatoes in order to develop improved methods of storage of the crop. This work is therefore aimed at investigating the possible changes in


quality and nutritional composition of sweetpotatoes during storage using different storage methods.


1.3Objective of the Study


The objective of the study was to determine the yield and storability of two sweetpotato cultivarsas influenced by chicken manure and inorganic fertilizer in the sweetpotato production forest transitional agro- ecological zone of Ghana.



1.3.1    Specific Objectives


The specific objectives are to:


  1. Compare the effectiveness of organic (chicken manure), inorganic fertilizers and integrated nutrient management for improvement of soil fertility on
  2. Determine the varietal response of sweetpotato root tubers to organic (chicken manure), inorganic fertilizers and integrated nutrient
  3. Compare the effectiveness of pit, ash, and grass storage methods for sweetpotato root tubers in terms of: The rate of water loss in the root ubers, weight change, root tuber sprouting, the rate of rotting of root tubers and pest infestation of root
  4. Assess the effect of soil amendments on the quality of sweetpotato


  1. Assess the effect of storage methods (Ash, Grass and Pit) on the nutrient levels of sweetpotato root
  2. Determine the financial implication of combined use of chicken manure and inorganic fertilizer on the yield of

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