Soil GHG fluxes under organic & non-organic agriculture compared: First results from measurements taken in the DOK-Experiment

Summary

Soil management induces nitrous oxide (N2O) and methane (CH4) emissions that account for around 40% of agriculture's direct greenhouse gas (GHG) emissions globally. Nitrous oxide is formed in the soil through a multitude of aerobic and anaerobic microbial processes with broadly varying shares and rates depending on atmospheric and site-specific conditions. Generally, N2O fluxes show a high spatial and temporal variability. A robust finding is that lower nitrogen application rates are associated with lower nitrous oxide emissions.
Organic farming systems provide multiple environmental benefits; they foster inter alia agriculture’s mitigation potential concerning climate change. Skinner et al. (2014) evaluated with Meta-Analysis the available global dataset from field measurements comparing organic with non-organic (with synthetic fertilisers and herbicides) agricultural management. They found with high significance that area-scaled nitrous oxide emissions from organically managed soils are 497 ± 160 kg ha-1 a-1 CO2-eq. lower than under non-organic management. Meta-Regression indicated that the main driver of N2O emissions under non-organic farming was N-input, whereas for organic farming concentrations of total soil N and soil organic C (SOC) were responsible. This can be explained by the high bioavailability of synthetic fertiliser and the retarded mineralisation of the N inputs in organic systems; a decoupling in time of N input and consumption.
Since August 2012 soil GHG fluxes, N2O, CH4 and CO2, are being sampled in the DOK experiment at Therwil CH. This farming system comparison trial of organic and non-organic treatments was established in 1978. The good documentation of crop management and inputs will be of advantage, e.g. for the endeavour to close knowledge gaps concerning N fluxes and pools in soils under organic management. We present first results from measurements in a winter wheat crop (second vegetation phase) and in a grass-clover corn crop-sequence, as timelines of the gas fluxes underlined with corresponding variables, as well as cumulated values with tested significance of differences.