Tree species diversity, topsoil conditions and arbuscular mycorrhizal association in the Sidama traditional agroforestry land use, southern Ethiopia
Zebene, Asfaw (2003). Tree species diversity, topsoil conditions
and arbuscular mycorrhizal
association in the Sidama traditional agroforestry land use, southern Ethiopia.
Diss. (sammanfattning/summary) Uppsala
: Sveriges lantbruksuniv.,
Acta Universitatis agriculturae Sueciae. Silvestria, 1401-6230 ; 263
ISBN 91-576-6347-5
[Doctoral thesis]
ISBN 91-576-6347-5
[Doctoral thesis]
|
Abstract
Sidama farmers cultivate
trees to meet their food, wood, fodder and other service needs. Tree
cultivation intensity has increased during the past three decades. Significant
positive correlation was found between farm size and number of species, and
number of stems per farm. The number of tree species per farm averaged 16 and
ranged from 4 to 28. Within farms, about ten different field types were
identified of which enset fields contain the highest
number of species. Wealthy households have more tree species than poor
households. In general the largest number of tree species, the largest number
of stems and the largest basal area ha⁻¹ were recorded on farms
of wealthy households. Based on farmers´knowledge and
laboratory studies, nutrient accumulation in the topsoil under Cordia africana, Millettia ferruginea and
Eucalyptus camaldulensis managed under three agroforestry
practices (AF) on different farms at three sites was evaluated. Significantly
higher concentration of P was observed under Millettia
and Cordia than under Eucalyptus. pH
under Millettia and Cordia
were significantly higher than under Eucalyptus at one site. Topsoil under Millettia and Cordia also had
significantly higher levels of exchangeable Ca and Mg
than Eucalyptus. For scattered AF soil and enset,
plants were sampled at laterally increasing distances from the tree trunks and
outside the canopy on enset and maize fields. Under
canopies of both Cordia and Millettia
trees, the diameter of enset was significantly
greater than that of enset plants grown in open
fields. Topsoil under canopies of scattered Cordia
and Millettia trees, compared with open fields,
generally had higher pH, CEC, increased total N, organic C and available P, but
had no effect on some exchangeable bases. Six tree-crop combinations and two
open-maize plots in enset and maize fields were
selected to study the level of indigenous arbuscular mycorrhizal (AM), number of spores and levels of root
colonization. At field level, tree-crop combinations induced a higher number of
spores and level of colonization than in an open-maize field. The proportions
of roots were in the following order: tree-enset-coffee
> tree-enset > tree-maize for Cordia trees and tree-enset >
tree-enset-coffee > tree-maize for Millettia trees. Beneath both Cordia
and Millettia trees scattered on maize fields, the
proportion of colonized root decreased with increasing distances laterally from
the tree trunks. At nursery level, significantly higher levels of root
colonization were observed for maize plants grown on soil from beneath tree enset-coffee and enset plots than
those grown on soil from tree-maize and open-maize plots. The percentage of AM
colonized roots of maize was significantly positively correlated with the
number of spore counts for field soils.
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