Carbon Sequestration in Agroforestry Systems between Conservation Agriculture and Conventional Practice in The Asal Area of Machakos County, Kenya

Abstract

Dryland ecosystems have always been prone to relatively high vegetation and general environmental degradation; translating to changes in soil physical and chemical properties and massive carbon losses. Despite their vast surface area, Carbon sequestration therein still remains low. However, this low carbon means they are less saturated and therefore a tremendous potential therein to sequester more Carbon. Conservation agriculture with trees (CAWT) presents an opportunity to reduce the degradation and enhance the carbon stocks. This study was set to compare the biomass productivity and carbon sequestration potential of agroforestry between conventional and conservation agriculture practice. The  study was carried out as part of ongoing experimentation established in short rain (SR) season of 2012 by the World Agroforestry Centre in a trial site at the Agricultural Training Centre (ATC) in Machakos county, Kenya. The trials adopted a split plot arranged in a randomized complete block design with two farming systems (conventional and conservation agriculture) as the main blocks, 7 treatments and three replicates, summing to a total of 42 plots. In the fields, two shrub species (Calliandra calothyrsus Meissn. and Gliricidia sepium Jacq.) were planted in three different spacing (1.5x1 m, 3x1 m, 4.5x1 m) for maize-legume intercrops. Trees were harvested by coppicing, weighed and leaf/twig samples taken for determination of biomass, which was then converted to Carbon using a conversion factor 0.5. The data was statistically analyzed using ANOVA and means separated using LSD at p <0.05. Results showed significant increase in carbon sequestration under conservation agriculture (p <0.001), with a yearly sequestration potential of between 12.8 and 24 Mg C/ha/yr compared to 11.6-23 Mg C/ha/yr for conventional practice. Calliandra also sequestered more carbon than Gliricidia. CAWT is therefore concluded to be a feasible way of increasing carbon stocks in the drylands.