This study combines research on soil physical and chemical properties as affected by four Eucalyptus species in Ruhande arboretum. The soil samples for research properties were taken from 0-20 cm depth using auger and one undisturbed core from each sampling unit was taken for the analysis of soil bulk density. Soil bulk density and moisture did not differ significantly between all treatments. Sand proportions differed significantly only between E. tereticornis and E. maidenii whereas silt and clay were non-significant. The soil under Eucalyptus was sandy, with sand proportion ranging from 66.4-71%. Bulk density increased with increasing sand whereas moisture content showed a reverse trend. The soil samples for studying chemical properties were taken as described in Nsabimana et al. 2008. All chemical parameters except base saturation differed significantly between treatments. Soil pH was strongly acidic but rich in total nitrogen and organic carbon which was attributed to higher litter production, its relatively faster rate of decomposition, and greater amount of residues produced by the eucalypts. Carbon/nitrogen ratio, CEC, and BS were high under all treatments while the available phosphorus was lower which was attributed to the low pH. Future studies should test if the species similarly affect the soil or not and confirm if the species increase soil nutrients. Benchmarked study sites should be used to enable differences in the species effects on the site if any.

This study was conducted in Musanze district, Rwanda, to evaluate the net benefits of silky oak (Grevillea robusta) production for small farmers. A semi-structured questionnaire was administered to 100 households distributed in four villages. The cost-benefit ratio was used as a decision-making tool. A diameter tape and a Haga altimeter were used to measure the DBH and height of grevillea and other dominant agroforestry tree species. Results indicate that 66 % of laborers were family members, gaining 625 Rwf per person day with grevillea production (US$ 0.61, with 4-8 hours of work per day. Also, results show that farmers earn 57,950 Rwandan Francs (Rwf) per hectare per year (US$ 57.48 from grevillea products (stakes, poles, charcoal, and timber), whereas the mean investment in grevillea production is 54,200 Rwf ha-1 year-1 (US$ 53.76. The net farm income is 3,225 Rwf (US$ 3.2 ha-1 year-1. The net benefit from grevillea product is affected by poor farmer data record as the majority of67% of respondents has not attended any formal education. However, farmers gain additional benefits of US$ 628, US$ 298, and US$ 224ha-1 year-1 from potatoes, maize, and bean, respectively, depending on their crop choice during intercropping with grevillea. The benefit-cost ratio is 1.06, which highlights the modest profitability of growing grevillea on the farm. In addition, soil erosion control, soil fertility increase, landslide prevention, shade provision, microclimate improvement, and biodiversity conservation were reported as ecosystem services of grevillea on the farm. Growth performance of grevillea (diameter at breast height, tree height, and volume) is analyzed in all four villages. The study shows that growing grevillea is profitable for smallholder farmers via tree products and farm benefits, including ecosystem services aspects.