The Agronomic qualities of the Mexican Sunflower (Tithonia diversifolia) for soil fertility improvement in Ghana: an exploratory study
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Date
2010
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Abstract
Soil fertility depletion remains a major biophysical constraint to increased food
production in Ghana even when improved germplasm has been made available.
With the growing concern of the potential of low input agriculture in mitigating
soil fertility challenges, exploratory researches are imperative in selecting best
quality organic materials that meet this expectation. This study was conducted
to assess the suitability of Tithonia diversifolia green biomass as a nutrient
source for smallholder agriculture in Ghana using both on-station and on-farm
trials. The on-station research comprised an evaluation of the decomposition
and nutrient release patterns of T. diversifolia in comparison with well-known
leguminous species of agroforestry importance: Senna spectabilis, Gliricidia
sepium, Leucaena leucocephala and Acacia auriculiformis. Concurrently, field
trials were conducted to appraise the quality of T. diversifolia green biomass in
relation to its biophysical effects on soil properties and the agronomic
characteristics of crops. This was a comparative study with S. spectabilis, G.
sepium and mineral fertilizer on a ferric acrisol. Field trials were also
conducted to determine best practices for optimum biomass production of T.
diversifolia using different pruning regimes and cutting heights as factors. The
on-farm research was conducted at Dumasua in the Brong Ahafo Region of
Ghana to appraise 200 farmers’ preliminary knowledge of T. diversifolia and
evaluate the effect of T. diversifolia green biomass on soil fertility indicators
and crop yields. The results of the decomposition study confirmed significantly
high N, P, K concentrations in T. diversifolia comparable to levels recorded for
the four leguminous species. In addition, T. diversifolia recorded the highest
decomposition and nutrient release rates which differed significantly (p < 0.05)
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from rates of the four leguminous species. Although decomposition and
nutrient release rates of species were related to quality of leaf material, P and
Mg concentrations in particular were most influential in decomposition and
nutrient release based on significant results. The on-station trials showed
significant effect of the green manures (particularly T. diversifolia) on soil
properties and the biomass and fruit yield of okro (Abelmoschus esculentus).
These results were comparable and in some cases greater than fertilizer
treatments. Total yield response in T. diversifolia treatment was 61% and 20%
greater than the control and fertilizer treatments respectively. From the pruning
experiment, it was evident that height of cutting, pruning frequency and their
interaction significantly affected dry matter production of T. diversifolia. Dry
matter production was highest (7.2 t ha-1yr-1) when T. diversifolia was pruned
bi-monthly at 50 cm height. Results from the sociological survey confirmed
farmers’ general knowledge on T. diversifolia at Dumasua was poor. Although
majority of respondents had seen the plant growing, none could give a common
name. Only the ornamental importance of T. diversifolia was identified.
Meanwhile, the on-farm trials revealed a significant synergistic effect of
combining T. diversifolia and fertilizer on soil nutrient availability and harvest
index of maize. The results showed that the application of Tithonia either alone
or in combination with fertilizer can increase yield by 24% and 54%
respectively compared to plots which received no inputs.
Description
A Thesis submitted to the Department of Agroforestry, Kwame Nkrumah
University of Science and Technology in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Agroforestry