Papers

Modelos de decaimento de primeira ordem aplicado a descrição da perda de C-CO2 do solo após preparo com enxada rotativa

Author: Newton La Scala Jr., Afonso Lopes, Kurt Spokas, David Walter Archer e Donald Reicosky

Keywords: soil respiration, soil tillage, soil organic matter, labile carbon decay.

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Summary

To further understand the impact of tillage on CO2 emission, the applicability of two conceptual models was tested, which describe the CO2 emission after tillage as a function of the non-tilled emission plus a correction due to the tillage disturbance. Models assume that C in readily decomposable organic matter follows a first-order reaction kinetics equation as: dCsoil (t) / dt = -k Csoil (t), 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) and k is the decay constant (time–1). Two possible assumptions were tested to determine the tilled (FT) fluxes: the decay constants (k) of labile soil C before and after tillage are different (Model 1) or not (Model 2). Accordingly, C flux relationships between non-tilled (FNT) and tilled (FT) conditions are given by: FT = FNT + a1 e–a2t (model 1) and FT = a3 FNT e–a4t (model 2), where t istime after tillage. Predicted and observed CO2 fluxes presented good agreement based on the coefficient of determination (R2 = 0.91). Model comparison revealed a slightly improved statistical fit of model 2, where all C pools are assigned with the same k constant. Rotary speed was related to increases in the amount of labile C available and to changes of the mean resident labile C pool available after tillage. This approach allows describing the temporal variability of tillage-induced emissions by a simple analytical function, including non-tilled emission plus an exponential term modulated by tillage and environmentally dependent parameters.