Effect of tectona grandis leaf extract, mulch and woodlot soil on germination and growth of maize.

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June, 2009.
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The Allelopathic effects of Tectona grandis leaves were tested on maize seedlings in the laboratory, on field soil mulched with Tectona prunings and on top soil, sub-soil from garden soil and Tectona woodlot. The laboratory experiment was conducted in sterilized Petri dishes. The effects of the different concentrations of aqueous extracts 25%, 50%, 75%, and 100% were compared to distill water (control). The aqueous extracts caused significant inhibitory effects on germination, shoot and root elongation, root and shoot dry weight upon increasing the concentration of the extracts of 10 day old maize seedling. Bioassay indicated that the inhibitory effect was proportional to the concentration of the extracts and higher concentrations 75%-100% had the stronger inhibitory effect whereas, in some cases the lower concentration 25%-50% showed stimulatory effect. The study also revealed that inhibitory effect was much pronounced in root rather than shoot growth. The field studies tested Tectona grandis mulch on weed control. The results indicated that different rates of Tectona mulch rate had significant effects on weeds. In the field, the height, diameter, shoot dry weight, root dry weight and yield of maize not significantly (P≥0.05) affected because the addition of mulch had a beneficial effect by providing nutrients during decomposition. Comparison of soils under Tectona woodlot and garden soil indicated that there is no significant (P≥0.05) between the means. All the parameters studied, that is height, diameter, shoot and root dry weight were similar. Finally, it was hypothesed that, there is no allelopathic effect of soils under Tectona grandis woodlot on maize growth. Generally, within 0.15cm soil depth, shoot dry weight, root dry weight, height and diameter showed no significant (P≥0.05) differences between mean. Therefore, the hypothesis was accepted since, the means were similar. Also, within 15 – 30cm soil depth, shoot dry weight, root dry weight, height and diameter showed no significant (P≥0.05) differences between mean. Therefore, the hypothesis was accepted because, the means were similar and allelochemicals in soils are rapidly lost near soil surface and soil organisms are capable of detoxifying allelochemicals in soil. Based on the overall finds of this research, these conclusions were drawn. Firstly, allelopathy is a concentration – dependent phenomenon. The allelochemicals present in Tectona grandis can have an allelopathic inhibitory effect on different crops associated with Tectona plantation and also different agroforestry systems in field conditions. Secondly, addition of Tectona grandis mulch in the field had a beneficial effect on maize since; the allelochemicals in the mulch are transient. It is known that Tectona grandis mulch have the ability to control weeds. Finally soil under Tectona grandis woodlot has no effect on crops.
A thesis submitted to the School of Postgraduate Studies, Kwame Nkrumah University of Science and .Technology, Kumasi in partial fulfillment of the requirement for the Master of Science Degree in Agroforestry on