Organic and Conventional Agriculture Systems Effects On Soil Carbon Dynamics and Greenhouse Gas Emissions.

The majority of organic and conventional agriculture system comparisons are long-term experiments (>10 years). Therefore it is imperative to understand short-term impacts on soil and environmental quality during the transition period from a conventional system to a 3-year, USDA-NOP certified organic system. The objective of this study was to determine short-term effects during the transitional period from a conventional system to an organic system on crop production, greenhouse gas (GHG) emissions, and soil carbon dynamics. The project was implemented in April 2010 in a RCBD at the Iowa State University Horticulture Research Station (Gilbert, IA). The experimental layout contained organic (O) or conventional (C) treatments and cropping rotations of corn and soybeans within main plots. Each main plot was split in two tillage types: tilled (T) (organic treatments consisted of rotavation and conventional treatments compromised of disking followed by field cultivation) and no-till (NT) systems. All organic plots contained a winter cover crop (winter rye and hairy vetch) and received composted poultry manure (2-3-4, N-P-K, respectively). For weed control, the O-NT utilized the winter cover crop which was rolled and crimped to create a surface mulch, whereas O-T used row cultivation. Commercial urea fertilizer (46-0-0, N-P-K) and synthetic herbicides were applied to the conventional system. Net ecosystem productivity ((above-ground biomass + below-ground biomass) – soil CO2 respiration) determined an annual carbon budget to quantify the storage or loss of organic carbon between both systems. Additionally, GHG emissions of soil N2O and CO2 efflux were monitored. Preliminary results include increased soil microbial biomass carbon (MBC) and soil organic carbon (SOC) in O-NT. Conventional crop grain yields were significantly greater than those in the organic systems. Results presented will also include particulate organic matter carbon (POM-C) and SOC through the soil-profile to assess carbon sequestration differences between organic and conventional agriculture systems.