Effects of conservation agriculture on crop yields, soil aggregation, and C & N dynamics in a soybean-maize rotation in western Kenya

Reduced tillage systems and controlled traffic farming (CTF) are being implemented in the Netherlands to lessen compaction and improve soil physical quality. Changes observed in soil physical quality after reducing tillage and starting controlled traffic are often attributed to ecosystem engineers such as earthworms. Through the burrowing and casting behaviours of diverse earthworm species these soil physical functions may be affected differentially between reduced tillage systems. It was hypothesized that reduced tillage systems, where soil is not inverted during tillage, and controlled traffic will promote earthworm density and diversity and therefore encourage an improvement in soil physical quality (soil water retention and infiltration). Two replicated field experiments in randomized complete block designs were performed on organic farms in Flevoland, the Netherlands. The soils are marine loams and climatic data was collected from nearby weather stations. Different tillage treatments with or without controlled traffic were compared. Earthworm abundance, biomass and species were assessed during biannual sampling in the spring and fall of 2009, 2010 and 2011. Soil water retention, infiltration, penetration resistance, aggregate stability and saturated hydraulic conductivity were measured in the fall of 2010 and spring of 2011. Controlled traffic showed a significant positive effect on earthworm density, infiltration capacity and reduced penetration resistance. Data on the effect of tillage system is thus far not conclusive, possibly due to insufficient time for changes to occur, however data from an additional season will be added for this conference