Growth and biomass production by young Eucalyptus tereticornis under agroforestry at Morogoro, Tanzania

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A trial involving Eucalyptus tereticornis was planted in a Latin square design with five treatment plots: (1) Eucalyptus monoculture kept free from weeds (clean-weeded); (2) Eucalyptus monoculture not given any weeding after planting (unweeded); (3) Eucalyptus clean-weeded and intercropped annually with beans; (4) Eucalyptus clean-weeded and intercropped annually with maize; and (5) Eucalyptus clean-weeded and intercropped annually with sorghum. After 3 years, trees representing all size classes were harvested from the trial and used to determine above-ground biomass production and nutrient content; other trees were excavated for root biomass determination. The whole experiment was later felled to determine height, basal area and volume production in each plot. Plot mean values were in the ranges 53–94% survival, 6.4–9.2 m height, 7.6–37.8 m 3 ha −1 volume, and 8.2–45.2 tha −1 total biomass. Unweeded plots showed unsatisfactory growth and survival throughout. Other treatments grew fast and at a rate comparable to young tree plantations reported for tropical and subtropical climates. Clean-weeded monocultures and Eucalyptus intercropped with beans gave the best growth in height, volume and biomass, showing statistical significance over Eucalyptus yields under intercropping with maize and sorghum. The production data satisfy the initial objective of providing high fuelwood and pole yields under short rotations. The trees showed compatibility with the food crops studied, although a wide spacing had been recommended earlier for sustained intercropping. Nutrient concentrations were considered adequate. The accumulation of N, Mg and Ca in the biomass was small compared to soil reserves. However, P and K contents in the biomass formed up to 123 and 34% of the respective soil ‘available’ reserves.