GREEN MANURE TERMINATION METHOD IMPACT ON SOIL CARBON AND SOIL BIOLOGY DYNAMICS

Abstract

No-till green manure (Gmr) termination creates a unique situation compared to conventional no-till agriculture due to the biomass of surface mulch generated. However, the impact this practice has on soil organic carbon (SOC) and soil organisms has been little researched and is the focus of the following thesis. Tillage regimes of fall tilled, spring tilled, or no-till were applied to a spring planted Gmr within a four-year grain rotation in two trials. Changes in three SOC pools were characterized for three years after GMr termination. Soil carbon was predicted to increase under no-till. This was seen only in Trial 2 where total carbon was greater under no-till compared to fall and spring till (by 2.4 Mg C ha-1 and 2.3 Mg C ha-1, respectively) and the effect remained significant all three years. The more labile permanganate oxidizable carbon was least responsive to termination. Soil microbial biomass (SMB), earthworms, beetles, and spiders were also analyzed after Gmr termination. It was predicted that soil organism abundance would increase under no-till termination. SMB was highest in the spring after Gmr termination in rotations that included hairy vetch/oat Gmr, regardless of tillage. Earthworm densities were negatively affected by tillage (88% and 86% less in Trial 1 and 2, respectively) but densities recovered three years after tillage to that of no-till plots. To further understand the impacts of tillage and presence of mulch on soil organisms a study with three levels of tillage (tilled, no-till, or fallow) and mulch present or absent was conducted. No effects of tillage were seen but earthworm density was greater under mulch in two out of three trials by 31% and 76% and spiders by 43% in one trial. Opiliones were analyzed in one trial only and were 29% less with mulch. This research has shown that the same soil benefits seen in conventional no-till management cannot be assumed in no-till Gmr termination. SOC in rotations that have high C inputs, such as Gmr, could be buffered against the impacts of tillage. Impacts on soil organisms vary by taxa and are a result of the mulch created, not tillage itself.