title: Tillage and crop residue management methods had minor effects on the stock and stabilization of topsoil carbon in a 30-year field experiment.
abstract: We studied the effects of tillage and straw management on soil aggregation and soil carbon sequestration in a 30-year split-plot experiment on clay soil in southern Finland. The experimental plots were under conventional or reduced tillage with straw retained, removed or burnt. Wet sieving was done to study organic carbon and soil composition divided in four fractions: 1) large macroaggregates, 2) small macroaggregates, 3) microaggregates and 4) silt and clay. To further estimate the stability of carbon in the soil, coarse particulate organic matter, microaggregates and silt and clay were isolated from the macroaggregates. Total carbon stock in the topsoil (equivalent to 200 kg m(-2)) was slightly lower under reduced tillage (5.0 kg m(-2)) than under conventional tillage (5.2 kg m(-2)). Reduced tillage changed the soil composition by increasing the percentage of macroaggregates and decreasing the percentage of microaggregates. There was no evidence of differences in the composition of the macroaggregates or carbon content in the macroaggregate-occluded fractions. However, due to the higher total amount of macroaggregates in the soil, more carbon was bound to the macroaggregate-occluded microaggregates in reduced tillage. Compared with plowed soil, the density of deep burrowing earthworms (Lumbricus terrestris) was considerably higher under reduced tillage and positively associated with the percentage of large macroaggregates. The total amount of microbial biomass carbon did not differ between the treatments. Straw management did not have discernible effects either on soil aggregation or soil carbon stock. We conclude that although reduced tillage can improve clay soil structure, generally the chances to increase topsoil carbon sequestration by reduced tillage or straw management practices appear limited in cereal monoculture systems of the boreal region. This may be related to the already high C content of soils, the precipitation level favoring decomposition and aggregate turnover in the winter with topsoil frost.
authors.affiliation: School of Environmental Sciences, Jawaharlal Nehru University, New Delhi, India; Natural Resources Institute Finland (Luke), Natural Resources and Bioproduction, FI-31600, Jokioinen, Finland. Electronic address: pssinghpooja@gmail.com.
authors.forename: Pooja
authors.initials: P
authors.lastname: Singh
authors.affiliation: Natural Resources Institute Finland (Luke), Natural Resources and Bioproduction, FI-31600, Jokioinen, Finland. Electronic address: jaakko.heikkinen@luke.fi.
authors.forename: Jaakko
authors.initials: J
authors.lastname: Heikkinen
authors.affiliation: Natural Resources Institute Finland (Luke), Natural Resources and Bioproduction, FI-31600, Jokioinen, Finland. Electronic address: elise.ketoja@luke.fi.
authors.forename: Elise
authors.initials: E
authors.lastname: Ketoja
authors.affiliation: Natural Resources Institute Finland (Luke), Natural Resources and Bioproduction, FI-31600, Jokioinen, Finland. Electronic address: visa.nuutinen@luke.fi.
authors.forename: Visa
authors.initials: V
authors.lastname: Nuutinen
authors.affiliation: Natural Resources Institute Finland (Luke), Natural Resources and Bioproduction, FI-31600, Jokioinen, Finland. Electronic address: ansa.palojarvi@luke.fi.
authors.forename: Ansa
authors.initials: A
authors.lastname: Palojärvi
authors.affiliation: Natural Resources Institute Finland (Luke), Natural Resources and Bioproduction, FI-31600, Jokioinen, Finland. Electronic address: jatta.sheehy@luke.fi.
authors.forename: Jatta
authors.initials: J
authors.lastname: Sheehy
authors.affiliation: Natural Resources Institute Finland (Luke), Natural Resources and Bioproduction, FI-31600, Jokioinen, Finland. Electronic address: martti.esala@luke.fi.
authors.forename: Martti
authors.initials: M
authors.lastname: Esala
authors.affiliation: School of Environmental Sciences, Jawaharlal Nehru University, New Delhi, India; Department of Environmental Science, Tezpur University, Assam, India. Electronic address: sudipmitra@yahoo.com.
authors.forename: Sudip
authors.initials: S
authors.lastname: Mitra
authors.affiliation: Department of Agricultural Sciences, University of Helsinki, Finland. Electronic address: laura.alakukku@helsinki.fi.
authors.forename: Laura
authors.initials: L
authors.lastname: Alakukku
authors.affiliation: Natural Resources Institute Finland (Luke), Natural Resources and Bioproduction, FI-31600, Jokioinen, Finland. Electronic address: kristiina.regina@luke.fi.
authors.forename: Kristiina
authors.initials: K
authors.lastname: Regina
keywords: Earthworm activity; Microbial biomass carbon; Particulate organic matter; Reduced tillage; Soil aggregation; Soil carbon; Stubble management