. The Canadian field-naturalist. Natural history. 10cm 1998. JJASONDJFMAMJJAS 1998 1999 Control Spring Summer Autumn Figure 6. Mean monthly soil temperatures at 10 cm and 50 cm in the control and spring, summer and autumn burns. prairie reported by Rice and Parenti (1978). In the first growing season mean monthly soil temperatures at 50 cm increased to a maximum of °C in the sum- mer plot in August compared to maximum values of °C in the control and °C and °C, respec- tively, for the autumn and spring burns (Figure 6). By mid-winter the mean 50 cm soil temperature in the autumn
. The Canadian field-naturalist. Natural history. 10cm 1998. JJASONDJFMAMJJAS 1998 1999 Control Spring Summer Autumn Figure 6. Mean monthly soil temperatures at 10 cm and 50 cm in the control and spring, summer and autumn burns. prairie reported by Rice and Parenti (1978). In the first growing season mean monthly soil temperatures at 50 cm increased to a maximum of °C in the sum- mer plot in August compared to maximum values of °C in the control and °C and °C, respec- tively, for the autumn and spring burns (Figure 6). By mid-winter the mean 50 cm soil temperature in the autumn burn had dropped to °C, which was about °C colder than the other burned plots and almost 4°C colder than the control. Differences in 50 cm soil temperatures were less marked in the second growing season. Temperature differences between plots may be attrib- uted to the insulating effect of the litter and snow cover. A mulch of litter helps to reduce loss of both sensible and latent heat as well as radiative heat loss from the soil. Kohnke and Werkhoven (1963) demonstrated that soil temperature at a depth of 10 cm was the same as that recorded at cm under a straw mulch of kg nr2. Similarly, Unger (1978) reported that winter soil temperatures increased by approximately °C for each kg of straw mulch applied. Snow provides better insulation for strawberry plants than straw mulch under severe winter conditions (Boyce and Linde 1986). The thermal diffusivity of straw is about 5 x 106 m2s1 and ranges from 4 x 10~7 mV1 for fresh snow to over 5 x 10~7 mV1 for a mature snowpack (List 1966). In addition, solar radiation will penetrate a translucent snowpack and provide a net radiative heat gain (Marchand 1984; Oke 1978). Water vapor also moves upwards from the deep warmer soil towards the colder surface and releases latent heat when it con- denses. If snow arrives before freezing occurs, some of this heat is retained within the soil. At the end of the first
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