Tree species and pruning regime affect crop yield on bench terraces in SW Uganda |
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| Authors: | D Siriri C K Ong J Wilson J M Boffa C R Black |
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| Institution: | (1) World Agroforestry Centre, P. O. Box 26416, Kampala, Uganda;(2) World Agroforestry Centre, P. O. Box 30677, Nairobi, Kenya;(3) Centre for Ecology and Hydrology, Bush Estate, Penicuik, EH26 0QB, UK;(4) Plant and Crop Sciences Division, University of Nottingham, Sutton Bonington Campus, Nottingham, LE12 5RD, UK; |
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| Abstract: | Integration of trees on farms may exert complementary or competitive effects on crop yield. This 4 year study examined novel
systems in which Alnus acuminata (alnus), Calliandra
calothyrsus (calliandra), Sesbania sesban (sesbania) or a mixture of all three were grown on the degraded upper part of bench terraces in Uganda; beans or maize were
grown on the more fertile lower terrace during the short and long rains. Three pruning treatments (shoot, root or shoot + root
pruning) were applied to the tree rows adjacent to the crops; shoot prunings were applied as green manure to the woodlot from
which they came. Pruning increased survival in calliandra and reduced survival in sesbania; alnus was unaffected. Pruning
reduced tree height and stem diameter in alnus, but did not affect calliandra or sesbania. Maize yield adjacent to unpruned
calliandra, alnus and sesbania or a mixture of all three was reduced by 48, 17, 6 and 24% relative to sole maize. Shoot pruning
initially sustained crop performance but shoot + root pruning became necessary when tree age exceeded 2 years; shoot + root
pruning increased maize yield by 88, 40, 11 and 31% in the calliandra, alnus, sesbania and tree mixture systems relative to
unpruned trees. Bean yield adjacent to unpruned calliandra, alnus, sesbania and the tree mixture was 44, 31, 33 and 22% lower
than in sole crops and pruning had no significant effect on crop yield. The results suggest that sesbania fallows may be used
on the upper terrace without reducing crop yield on the lower terrace, whereas pruning of alnus is needed to sustain yield.
Calliandra woodlots appear to be unsuitable as crop yield was reduced even after pruning. |
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