Tag: alnus acuminata
Alnus acuminata: an effective fertilizer tree for smallholder farmers in sub-humid regions of Rwanda
The agronomic and economic potential of tree fallows on scoured terrace benches in the humid highlands of Southwestern Uganda
Smallholder farmers in the densely populated highlands of Southwestern Uganda face major constrains because of poor soil productivity and inadequate wood supply. The wood production, soil replenishing potentials and economic returns of five improved fallow systems: Sesbania sesban, Calliandra calothyrsus, Alnus acuminata, Tephrosia vogelii, and Acanthus pubescens were compared with the traditional bush fallow and continuous cropping systems. A trial was conducted on a non-P deficient Haplorthox (USDA) or Haplic ferralsols (FAO). Starting in March 1996, the fallow phase lasted for 2 years. Crop performance after fallow was subsequently assessed for 2 years. Soil improvement due to fallow was observed only on the degraded upper two-thirds of the terraces but not on the relatively more fertile lower terrace parts. Mineral nitrogen levels increased from 9.5 mg kg1 in the continuous cropping systems to 17.3 and 13.1 in the Sesbania and Calliandra fallows, respectively. On the upper terrace, cumulative maize yield after fallow increased significantly from 1.6 Mg ha1 in the continuous cropping to 3.5, 4.1, 5.9 and 6.2 Mg ha1 in the Tephrosia, Alnus, Calliandra and Sesbania fallow systems, respectively. Besides crop yield improvement, Sesbania, Calliandra and Alnus resulted in high firewood production of 27, 26, and 24 Mg ha1, respectively. Net benefits over the whole terraces show negative annual returns under the continuous cropping system but higher net returns of USD 229, 157, and 111 in the Sesbania, Calliandra and Alnus systems, respectively. Returns to labour are also higher in the tree fallow system, trading labour above the normal wage rate. On the upper terrace part, only Sesbania, Calliandra and Alnus systems result in positive annual net benefits of USD 185, 111, and 53, respectively. Tephrosia, natural fallow and continuous cropping systems are not profitable on the heavily degraded upper terrace as they result in negative returns.
Tree species and pruning regime affect crop yield on bench terraces in SW Uganda
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
Alnus acuminata
Alnus acuminata is a fast-growing, medium-sized tree that grows up to 25 m in height, with a 50-60 cm diameter measured at breast height (DBH). The trunk is cylindrical and straight with a slightly swollen base, and the pyramidal crown has few well-developed branches. The bark is light grey or silver with yellowish lenticels. Leaves are simple, alternate, elliptical, 6-15 cm long, 3-8 cm wide, border double dentate, deciduous or semi-deciduous. The buds are sparsely ferruginousvelutinous. Male and female flowers occur in separate catkins on the same branch.