Effect of soil amendments on the quality of three commonly cultivated lettuce cultivars

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The effect of soil amended with poultry manure and NPK fertilizer on the quality of three cultivars of lettuce; Great Lake, Eden and Trinity cultivated in KNUST, were assessed and analysed. The cultivars were raised, harvested and stored at the Department of Horticulture of the Kwame Nkrumah University of Science and Technology, Kumasi. The harvested leaves were assessed for calcium, iron, vitamin C, chlorophyll, carotenoid level, weight loss and dry matter content as well as E. coli and faecal enterococci contamination. The treatments showed a significant effect (p<0.05) on the quality parameters except weight loss, dry matter content, E. coli and faecal enterococci load. The cultivars also varied (p<0.05) with regards to the quality indicators assessed. Similarly, the interaction of the treatments and cultivars showed significant differences. The results revealed the stream water used for irrigation as the lead source of the bacterial contaminants. The highest level of E. coli and faecal enterococci contamination ranged from 4.09 – 4.58 log cfu/g and 2.49 – 2.56 log cfu/g while the lowest loads recorded were 0.50 – 0.90 log cfu/g and 1.57 – 1.81 log cfu/g, respectively. Great Lakes harvested from plots amended with NPK was the only sample to have had no E. coli pathogens. Only few of the samples recorded contamination level below the satisfactory microbiological hygiene critical level of 2 log cfu/g.
A thesis submitted to the School of Research and Graduate Studies, Kwame Nkrumah University of Science and Technology, Kumasi, in partial fulfillment of the requirements for the award of Master of Philosophy (Mphil.Post Harvest Technology) degree