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

La Scala, N., Lopes, A., Spokas, K., Bolonhezi, D., Archer, D.W., Reicosky, D.C.
Soil & tillage research 2008 v.99 no.1 pp. 108
carbon dioxide, gas emissions, soil respiration, tillage, greenhouse gases, soil-atmosphere interactions, carbon, losses from soil, prediction, models, soil organic matter, degradation, equations
Tillage stimulates soil carbon (C) losses by increasing aeration, changing temperature and moisture conditions, and thus favoring microbial decomposition. In addition, soil aggregate disruption by tillage exposes once protected organic matter to decomposition. We propose a model to explain carbon dioxide (CO₂) emission after tillage as a function of the no-till emission plus a correction due to the tillage disturbance. The model assumes that C in the readily decomposable organic matter follows a first-order reaction kinetics equation as: dC sail(t)/dt =-kC soil(t) and that soil C-CO₂ emission is proportional to the C decay rate in soil, where C soil(t) is the available labile soil C (gm⁻²) at any time (t). Emissions are modeled in terms soil C available to decomposition in the tilled and non-tilled plots, and a relationship is derived between no-till (F NT) and tilled (F T) fluxes, which is: F T = a 1 F NT e - a 2 t , where t is time after tillage. Predicted and observed fluxes showed good agreement based on determination coefficient (R ²), index of agreement and model efficiency, with R ² 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 no-till plots (a ₂) and also to the amount of labile carbon added to the readily decomposable soil organic matter due to tillage (a ₁). These two parameters were estimated in the model ranging from 1.27 and 2.60 (a ₁) and -1.52x10⁻² and 2.2x10⁻² day⁻¹ (a ₂). The advantage is that temporal variability of tillage-induced emissions can be described by only one analytical function that includes the no-till emission plus an exponential term modulated by tillage and environmentally dependent parameters.