Structure, tree diversity, and aboveground carbon stocks of smallholder farms with push-pull technology in western Kenya

Abstract

Push-pull technology is a companion cropping system whose success in soil fertility improvement and management of agricultural pests has been established in cereal-based systems. Push-pull has also been proposed as a template for the sustainable intensification of agriculture in Africa. However, the application of the technology has remained on a field scale and is restricted to cereal-based systems. Trees in agricultural landscapes are considered a strategy for climate change mitigation by storing carbon in soils and woody biomass. However, their potential has not been quantified in push-pull systems. This study characterized 45 smallholder farms in western Kenya to establish the land use categories within which push-pull is integrated, the diversity and structure of perennials on the farms, and the aboveground carbon stored within those farms. The area of each land use category varied depending on the size of the land use category on each farm. The amount of carbon stored in aboveground biomass was estimated using an existing allometric equation. This study found that trees are integrated on farms with push-pull in homesteads (45), cropland (38), woodlots (26), boundaries (4), and grazing land (2) farms. A total of 9159 trees from 97 different species were recorded over 34 ha. Farms in Vihiga and Kisumu had more trees (38 % and 37 % of all trees recorded) than those in Siaya (25 %). There were more trees in woodlots (total=4518) and homesteads (total=3327), and the least in grazing land (total=18). Overall, the highest species richness, Shannon, and Simpson diversity were observed in the homestead (86 species, H’=2.52 and D = 0.86). Farms in Kisumu, Vihiga, and Siaya stocked an average of 12.1, 9.4, and 7.3 Mg C ha⁻¹ in aboveground biomass respectively. Variations were observed in land use categories, where woodlots had the greatest amount of carbon (55.5 Mg C ha⁻¹) while grazing land had the least (2.4 Mg C ha⁻¹). Eucalyptus spp., Grevillea robusta, and Markhamia lutea were the most dominant trees in abundance at 50 %, 16 %, and 11 % respectively. Conservation of trees on farms should be encouraged, as they protect biodiversity and store carbon thus contributing to climate change mitigation. This study's findings contribute to knowledge valuable to farmers and policymakers in making decisions on tree species and land use categories that have a high potential to sequester carbon in agroforestry systems.