Preliminary studies on rooting pattern and dry matter accumulation and distribution in Leucana Leucocephala, Gliricidia Sepium and Cassia Simea in the humid lowland of Ghana

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Germination and seedling growth characteristics, dry matter accumulation between above and below-ground portions, and root growth and distribution patterns in one year old seedlings of Leucaena leucocephala, Cliricidia sepium and Cassia siamea were studied on the Institute of Renewable Natural Resources’ Research Farm in Kumasi. Germination percentage was highest in Leucaena (93%), followed by Gliricidia (91%) and then Cassia (74%). Seedling component and total dry weight growth ranked in the order Gliricidia > Leucaena > Cassia. Relative growth rates of shoots, roots and whole plants differed significantly (P < 0.05) between species. Within each species root growth was proportionately greater than shoot growth. Shoot/root ratios decreased with increasing seedling dry weight. Field excavations showed that the bulk of total root biomass (63-96%) occurred in the 0-15cm soil depth. Total root excavations at 53 weeks after planting (WAP) showed that Leuceana, Gliricidia and Cassia had root systems reaching depths of 46.7, 53.5 and 50cm, and maximum leteral spreads of 98.2, 93.0 and 104.7cm, respectively. Thus even though competition between tree and crop roots should be expected in later years, roots of these species can act as “safety nets” for leached nutrients underneath shallow roots of annual crops, thereby improving nutrient use efficiency. The proportion of total dry weight in foliage decreased with age while the proportion in sterns and branches increased with age in all the species. Root nodules occurred on Leucaena and Gliricidia roots but not Cassia. While active nodules were observed on Gliricidia roots throughout the study period, no active nodules were found on Leucaena roots after 31 WAP. All the three species appear to be good for alley cropping and other agroforestry interventions. Thus other factors such as resistance to termite attack, provision of useful products (fodder, wood and stakes other than green manure) will determine the farmers’ choice of species for agroforestry systems in Ghana.
A thesis submitted to the Board of Postgraduate Studies, Kwame Nkrumah University of Science and Technology, Kumasi, in partial fulfilment of the requirements for the award of the Degree of Master of Philosophy in Agroforestry, 1993