Agriculture Reference
In-Depth Information
Figure I.23a compares the daily march of the temperature of a bare soil surface with
that beneath a surface mulch of standing dead foliage of the pasture legume Stylosanthes
hamata in tropical northeastern Australia (Bristow‚ 1988). The mulch effected a reduction
of 7.3 °C in the daily surface maximum at this date although this effect was much reduced
when the soils were wet. The daily temperature regimes of bare soil surfaces may be
even more severe than that presented above; Ross et al. (1985) recorded temperatures as
high as 60 °C at the surfaces of bare soils while surface mulches reduced this by as much
as 20 °C. In contrast‚ Figure I.23b compares the diurnal temperature changes at the sur-
face and beneath a moss cushion at the Shackleton Glacier site presented in Figure I.21a.
The amplitude of variation at the exposed soil surface is clearly greater‚ with lower
temperatures pertaining during the hours when the sun was low in the sky or not
incident on the site and higher and more variable temperatures when the surface was
exposed to greater incident radiation.
The influences of vegetation may be just as important over longer time intervals.
Bonneau (1979) considered that a forest canopy in a temperate climate may increase
winter soil temperatures by 1-2 °C and reduce those during summer by as much as
7-8 °C‚ compared with soils outside the forest.
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