Changes in soil C dynamics and N2O emissions under minimum tillage cereal crop production in boreal agroecosystems : Implications to climate change mitigation
Year: 2015
Type: dissertation
Abstract: Soils comprise more carbon (C) than any other terrestrial source and hence even a small change in the C content can be significant in regards to atmospheric CO2 concentration. Cultivated soils have lost soil organic carbon (SOC) during the latest decades in Finland. New cereal crop management practices, like no-till (NT) and reduced tillage (RT), can affect not only soil organic carbon (SOC) stocks and stabilization, but also nitrous oxide (N2O) emissions. The aim of this study was to gain better understanding about the changes in soil C dynamics and N2O emissions as a result of management practice changes in the boreal region, and the implications of these changes to climate change mitigation. Changes in SOC stocks and stabilization rates under different tillage (NT, RT, CT (conventional tillage with a moldboard plow)) and straw management (straw retention, straw removal, straw burning) practices, were studied at different sites with clayey and coarse textured soil across southern Finland. This was done by soil fractionation method (wet sieving and microaggregate isolation) to elucidate the composition of different soil fractions, namely large and small macroaggregates, microaggregates, silt and clay and macroaggregate-occluded soil fractions, and where the C is stored within them. The effects of Lumbricus terrestris on SOC were studied using the same method. Nitrous oxide fluxes were monitored biweekly for 2 years under CT, NT and RT practices using closed chambers. Measurements of several environmental and soil parameters were taken to study the underlying factors controlling the observed changes in soil C stocks and N2O emissions under the different management practices. Climate change mitigation potential through the studied cereal crop management practices seems small in the humid boreal region based on the results of this study. The minimum tillage treatments did not sequester SOC at any of the study sites which had been under NT or RT for a decade and the total C stocks were lower in the 0 15 cm topsoil layer at one clayey site under RT compared to CT after implementing RT for 30 years. All clayey sites had a fairly high SOC content originally and all sites had higher decomposition rate of crop residues in NT compared to CT, possibly hindering C sequestration. However, the aggregate stability was enhanced in NT cropping systems compared to CT, and NT increased the amount of SOC in large macroaggregates at several sites and in microaggregates within macroaggregates in the coarse textured site. L. terrestris mediated the formation of soil aggregates and the increase of SOC in the topsoil but possibly enhanced the decomposition rate in the soils. Cumulative N2O emissions were higher under NT compared to both CT and RT at the clayey sites and lower at the coarse textured site. However, the coarse textured site under NT received slightly less N fertilizer compared to CT. Increased N2O emissions under NT on clayey soils were likely due to denser soil structure with consistently higher soil moisture content and poor aeration. Therefore, mitigating N2O emissions requires special attention to soil structure and drainage. This study suggests that RT is a notable option to control N2O emissions. In the future, climate change could increase precipitation and freeze-thaw cycles in boreal agroecosystems possibly enhancing N2O fluxes and C losses of cultivated soils which puts pressure on finding new mitigation measures.
Source: Työväentutkimus Vuosikirja
Author: Jatta Sheehy
Language: English
Subfield: Soil Science
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W1950385631