Mulching is a common practice in organic farming to keep soils warmer when temperatures begin to drop. This will reduce the risk of freezing and therefore better seed germination. Temperature of mulched soils depends on thickness and physical properties of organic mulch. In this study variation of temperature in bare and mulched soil is compared by means of simulation model. Variation of the soil temperature around a constant average, Tav, at time t and depth x, Tx,t is (Koorevaar et al. 1993): Tx,t = Tav + Tamp * exp(-x/d) * sin (ωt –x/d) (1) where Tamp is the amplitude of sinusoidal wave, ω is the angular frequency of temperature wave, and d is the attenuation depth, ω and d can be expressed by Equations 2 and 3 (Leffelaar, 1993): ω = 2π /tc (2) d = (2λ / ω * Ch)1/2 (3) where tc is the time required for the wave to make a complete cycle, λ and Ch are conductance and the volumetric heat capacity, respectively. Soil was divided into layers of 2 cm depth and the model was run for bare soil and soil with 4-cm organic mulch at top. Soil temperature for layers was simulated for Tav = 0 °C with Tamp = 4.5 °C, model parameters were set as λ (soil) = 0.42, λ (organic mulch) = 0.25 J/(m s °C) and Ch (soil) = 1.05*106, Ch (organic mulch) = 2.5*106 J/m3 °C) (Leffelaar, 1993). Based on simulation results with an organic mulch layer of 4 cm no freezing occurs at a soil depth of 8-10 cm. However, in the bare soil no freezing would occur at a soil depth of 16-18 cm (Fig. 1). Large variation of temperature at soil surface will decrease with depth which is evident from amplitude of the wave both in bare and mulched soils. However, mulched soil will have less variation in day/night temperature at lower depth compare to bare soil (Fig. 1). Using simulation models it would be also possible to find out which mulch thickness is needed to prevent frost at shallower depths and what are the consequences of global warming on temperature of organically managed soils.

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