VARIABILITY OF SOIL TEMPERATURE WITH DEPTH ALONG A TRANSECT

Abstract
We studied the spatial variability of soil temperature along an 80-m transect on a bare field on an Olivier silt loam soil. We measured soil temperature at 68-cm intervals along the transect and at various soil depths. The spatial structure of temperature data was examined by semivariograms and autocorrelograms. Except for 20- and 30-cm soil depths, which exhibited a pure nugget effect, the temperature observations were found to be spatially interdependent. Moreover, a significant trend emerged for temperature measurements at the 10-cm soil depth. The semivariograms exhibited a nugget effect as much as 50% of sample variance. A spherical model was found to describe the overall shape of the semivariograms. The autocorrelation length obtained from a first-order autoregressive model with a white noise was found to describe the spatial structure of the soil temperature and gave results comparable to those obtained from the sphere of influence of semivariograms. The spatial structure was found at two scales: first a spatial dependency at small scale, manifested by the range of influence and autocorrelation length and not exceeding 25 m; and a second spatial structure at relatively larger scale, manifested by periodic behavior in temperature observation at 25 and 50 m.

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