Soil fertility and biodiversity on organic and conventional smallholder farms in Kenya

摘要

The growth of organic agriculture (OA) in sub-Saharan Africa (SSA) raises the question of how far OA can improve the livelihoods of the many smallholder farmers that have to cope with numerous complex biophysical and socioeconomic challenges. Evidence on the impacts of OA in SSA, particularly on soil fertility and biodiversity, still is scarce and inconclusive. The aim of this study was therefore to evaluate and compare soil fertility, decomposition and biodiversity between 20 organic and conventional farms in two counties (Kajiado and Murang'a) in Kenya. Soil sampled at 0-20 cm depth was analysed for physical and chemical properties. The decomposition of crop residues over 3 months was studied using litterbags while pitfall trapping and the derived diversity indices provided insights into arthropod abundance and diversity. Differences in soil properties, mass loss through decomposition, and arthropod abundance were analysed with linear mixed models. Findings show no statistically significant differences in soil fertility, decomposition and abundance of arthropods between organic and non-organic farms. However, species richness and diversity of arthropods on organic farms was significantly higher than on non-organic farms. Overall, farms in Kajiado had higher soil fertility and arthropod diversity than those in Murang'a, while farms in Murang'a had a higher arthropod abundance. It is argued that similar agricultural practices used in organic and non-organic farming systems, irrespective of county and biophysical conditions, strongly influenced soil fertility and biodiversity. Our results demonstrate that OA has the potential to increase arthropod biodiversity, but its ability to sustain the health of soils depends on numerous factors that are likely to undermine OA efforts in this region.