Improvement and Culture of Nitrogen Fixing Trees
Introduction
The term rotational woodlot connotes a technology which
involves growing trees, normally N-fixing, with crops for 2-3
years until the trees out-compete the crops. The woodlot may
then be used as a source of fuelwood, building poles or
fodder. Soil fertility is also restored during this time until the
farmers can cut the trees and start growing crops between the
stumps, 4 to 5 years later. The technology was designed to
mimic the traditional practice of shifting cultivation by
introducing trees into the crop and shrub land with shortened
fallow. The cropping and fallow phases take place
concurrently. This allows the farmers to crop for an extended
period without returning the land to bush fallow. The
technology is flexible in the sense that it allows the farmers to
adopt both the cropping phase and trees to suit individual
needs which diversifies production base, enhances trees and
crops productivity and allows a sustainable cropping system
(Ramadhani et al. 2002).
This technology is being promoted by the World Agroforestry
Centre (ICRAF) in collaboration with farmers, Tanzania
Forestry Research Institute (TAFORI), and the Agricultural
Research and Development Institute (ARDI) Tumbi. The
main objective is the provision of fuelwood for tobacco curing
and other domestic uses to rural farmers and improvement of
soil fertility in the tobacco-cereal land use system of Tabora,
Tanzania. It reduces pressure on the 'miombo' woodlands.
Despite the potential of this technology, there are few studies
on wood basic density and basal area on trees currently used
in rotational woodlots. Wood density is highly affected by
woodlot manipulation through silvicultural and cultural
practices. This study reports comparison of wood basic
density and basal area of 5-year-old N-fixing trees of Acacia
crassicarpa, A. julifera, A. leptocarpa, Leucaena pallida and
Senna siamea grown in rotational woodlots both on-station
and in farmers fields.