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Title: Short-term temporal changes of soil carbon losses after tillage described by a first-order decay model

Author
item LA SCALA, NEWTON - UNIV. OF SAO PAULO
item LOPES, AFONSO - UNIV. OF SAO PAULO
item Spokas, Kurt
item BOLONHEZI, DENIZART - UNIV. OF SAO PAUL
item Archer, David
item Reicosky, Donald

Submitted to: Soil & Tillage Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/8/2008
Publication Date: 3/24/2008
Citation: La Scala, Jr., N., Lopes, A., Spokas, K.A., Bolonhezi, D., Archer, D.W., Reicosky, D.C. 2008. Short-term temporal changes of soil carbon losses after tillage described by a first-order decay model. Soil & Tillage Research. 99:108-118.

Interpretive Summary: Elevated atmospheric carbon dioxide, potential global warming concerns and prospective use of soil as a sink for carbon attracted interest from farmers and land managers. Recent studies involving tillage methods indicate major gaseous loss of carbon immediately after tillage. Tillage stimulates soil carbon losses by increasing aeration, changing temperature and moisture conditions, and breaking soil aggregates. We propose a model to explain carbon dioxide emission after tillage as a function of the non-tilled emission plus a correction due to the tillage disturbance. Our hypothesis is that an additional amount of readily-decomposable organic matter is made available to the soil organisms by tillage which exposes aggregate-protected carbon, and thereby makes it accessible to microorganisms. The model assumes the readily-decomposable organic matter follows a simple first-order reaction kinetics equation and that soil emissions are proportional to the decay rate in soil. Predicted and observed fluxes showed good agreement based on determination coefficient, index of agreement and model efficiency. This method has the advantage that temporal variability of tillage-induced emissions can be described by only one simple analytical function that includes the non-tilled emission plus an exponential term modulated by tillage and environmentally-dependent parameters. These results are significant to farmers and policy makers in that intensive tillage results in substantial short-term gaseous losses of soil carbon. Farmers can develop and utilize new management techniques for enhancing soil carbon by changing tillage intensity to accommodate changing soil properties across a landscape. Farmers will benefit from the ability to cope with spatial variability and maintain crop production with minimal impact on the environment. This information will assist scientists and engineers in developing improved tillage methods to minimize the gaseous loss and to improve soil carbon management.

Technical Abstract: Tillage stimulates soil carbon (C) losses by increasing aeration, changing temperature and moisture conditions and breaking soil aggregates. We propose a model to explain carbon dioxide (CO2) emission after tillage as a function of the non-tilled emission plus a correction due to the tillage disturbance. Our hypothesis is that tillage exposes aggregate-protected C making an additional amount of readily-decomposable organic matter accessible to microorganisms. The model assumes that C in readily-decomposable organic matter follows a first-order reaction kinetics equation and that soil C-CO2 emission is proportional to the C decay rate in soil, where Csoil(t) is the available labile soil C (g m-2) at any time (t). Emissions are addressed in terms of soil C available to decomposition in the tilled and non-tilled plots, and a relationship is derived between non-tilled (FNT) and tilled (FT) fluxes where t is time after tillage. Predicted and observed fluxes showed good agreement based on determination coefficient (R2), index of agreement and model efficiency, with R2 as high as 0.97. The two parameters included in the model are related to the difference between the decay constant (k factor) of tilled and non-tilled plots (a2) and also to the amount of labile C added to readily-decomposable soil organic matter due to tillage (a1). These two parameters were estimated in the model ranging from 1.27 and 2.60 (a1) and -1.52 x 10-2 and 2.2 x 10-2 day-1 (a2). The advantage is that temporal variability of tillage-induced emissions can be described by only one analytical function that includes the non-tilled emission plus an exponential term modulated by tillage and environmentally-dependent parameters.