College of Forestry, Wildlife and Tourism

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Comparison of wood basic density and basal area of 5-year-old Acacia crassicarpa, A. julifera, A. leptocarpa, Leucaena pallida and Senna siamea in rotational woodlots trials in western Tabora, Tanzania
(World Agrofrestry Centre, 2006) Luhende, Raphael; Nyadzi, Gerson; Malimbwi, Rodgers E.
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.
Differential response to tree fallows in rotational woodlot systems In semi-arid Tanzania: post-fallow maize yield, nutrient uptake, And soil nutrients
(elservier, 2008) Kimaro, A.A.; Timmer, V.R.; Chamshama, S.A.O.; Mugasha, A.G.; Kimaro, D.A.
Agroforestry tree species producing high quality litter may enhance post-fallow soil nutrient availability and crop yields through mineralization of soil organic matter and green manure. A split-plot field experiment was used to evaluate maize yield and soil N and P status after fallowing indigenous and exotic tree species of contrasting litter quality. Responses were compared with recommended inorganic fertilizer use. The objective was to assess efficacy of 5-year tree fallows in improving soil productivity to screen species for increased crop yield under rotational woodlot culture, an agroforestry system mainly used for on-farm fuelwood production in semi-arid Tanzania. Post- fallow maize yield and soil nutrients differed significantly among tree fallows. Low C:N and L:N ratios enhanced nutrient release from slash. Acacia polyacantha (indigenous) and Gliricidia sepium fallows doubled maize yield compared to the natural fallow probably due to high soil N and P levels resulting from net release by high quality foliage. First season maize yield was similar to that from combined N and P fertilizers indicating high capacity of the fallows to improve crop yields and reduce fertilizer inputs usually unaffordable to small-scale farmers. Comparatively low maize yield and soil N and P levels after exotic Acacia crassicarpa and Acacia mangium fallows were attributed to net N immobilization by poor quality litter during growing seasons. This study suggests that rotational woodlot systems utilizing tree species with high litter quality can improve both post-fallow maize yield and soil fertility as well as produce sufficient fuelwood. In this aspect, A. polyacantha would be the most appropriate species.
Nutrient and water dynamics in rotational woodlots: A case study in western Tanzania
(Wageningen University, 2004) Nyadzi, Gerson Isaac
Rotations of trees and crops on farms are considered as a potential technology to overcome the shortage of wood, reverse deforestation of natural forests and improve soil fertility for food security enhancement in western Tanzania, sub-Saharan Africa. However, overexploitation of soil water resources and depletion of soil nutrients have been suggested as possible negative effects of growing trees on farms in the semi-arid tropics. Such possible pitfalls undermine and even threaten a successful implementation of the woodlot technology at larger scale. Evidently, without proper understanding of the interactions and possible competition between trees and crops, the potential benefits of this agroforestry technology will not be realized. Therefore, this study was focused on improving the understanding of trcc-soil-crop interactions by examining water and nutrient dynamics of various trees planted in rotational woodlots with a 5-year cycle. Field trials were established with five-year rotational woodlots. Five tree species were compared with natural fallow and continuous maize. Inter-cropping of maize between trees was possible for the first two years of tree establishment without sacrificing maize yield. There was no evidence that trees were over-exploiting the water reserves after three years. Transpiration was greatest in A. crassicarpa and was related to stem diameter, size of the tree canopy and soil water availability. Trees depleted relatively more waler than continuous maize and natural fallow, but were able to store more water after rains. Acacia trees had high litter fall but the leaves were low in P and N, which led to N and P immobilization during decomposition. Trees retrieved leached inorganic N and made better use of it than natural fallow and continuous maize. Wood production at the end of the five-year growing period ranged from 30 to 90 Mg ha-1 while C sequestered in the aboveground biomass during the same period ranged between 13 to 30 Mg ha-1. The rate of biomass production was highest for Acacia species while the foliage nutrient accumulation was highest for Leucaena species. The wood component varied greatly among species, ranging from 32 to 85% of the total tree biomass. Maize yields were higher after growing trees than after natural fallow and continuous maize when no fertilizers were applied. The benefits of tree fallows compared to natural fallows were modest, in terms of maize yield increases. The increase in crop yields after woodlots was attributed in part to higher soil inorganic N. Maize responded to fertiliser N and P. The agronomic efficiency was about 30 kg grain per kg N applied at a rate of 50 kg fertilizer N, and 15 kg kg-1 between 50 and 100 kg N applied. Application of more than 20 kg ha"1 of P or K did not significantly increase maize yields. The benefit of woodlots expressed in terms of maize yield was more pronounced at mid and lower slope positions than at upper slopes. The significance of rotational woodlots in improving soil fertility is limited by substantial accumulation of nutrients in wood. Nutrient mining by wood exportation istherefore a major threat for the sustainability of woodlots, when the exported nutrients are not supplemented via external sources. Medium-term rotational woodlots have the potential to meet the domestic and industrial wood needs and at the same time to reduce deforestation in Sub-Saharan Africa.
Nutrient use efficiency and biomass production of tree species for rotational woodlot systems in semi-arid Morogoro, Tanzania
(Springer, 2007) Kimaro, Anthony A.; Timmer, Vic R.; Mugasha, Ancelm G.; Chamshama, Shaban A. O.; Kimaro, Deborah A.
Frequent nutrient removals accompanying wood and crop harvests from rotational woodlot systems may contribute to declining site productivity and sustainability because of soil nutrient depletion. However, selecting for nutrient-efficient tree species may well sustain productivity under this system. To test this hypothesis, a randomized complete block experiment was adopted to assess effects of five tree species on soil nutrients status, nutrient use efficiency and wood yield in semi-arid Tanzania. After 5years rotation, top soils under Gliricidia sepium (Jaqua), Acacia polyacantha Willd. and Acacia mangium Willd. were the most fertile with soil organic carbon and exchangeable cation status raised close to those in natural Miombo systems. Soil inorganic N and extractable P levels reached sufficiency levels for subsequent maize culture. Wood productivity in tree fallows averaged three times higher than that of Miombo woodlands indicating the high potential of the woodlot system to supply fuelwood, and consequently relieve harvesting pressures on the natural forests. Acacia crassicarpa A. Cunn. ex Benth. produced the most wood (51Mgha−1) at low nutrient “costs” presumably due to high nutrient use efficiency. Wood yield of this species was 42 and 120% greater than that of A. polyacantha and A. nilotica, respectively, but contained comparatively less nutrients (42–60% less for P, K, and Ca). Gliricidia sepium and A. polyacantha returned the largest amount of nutrients through slash at harvests. Of all test species, A. crassicarpa exhibited the most promise to sustain wood production under rotational woodlot systems due to relatively high productivity and low nutrient export at harvest.

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