Agricultural Water Management, 6 (1983) 213--226 Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands 213 SPATIAL VARIABILITY OF PHYSICAL SOIL PROPERTIES INFLUENCING THE TEMPERATURE OF THE SOIL SURFACE H.F.M. ten Berge, L. Stroosnijder, P.A. Burrough, A.K. Bregt and M.J. de Heus INTRODUCTION The IJsselmeer polders in the centre of the Netherlands are highly productive agricultural lands. East Flevoland, one of these polders, was reclaimed only 25 years ago. The landscape is flat, the soil is of lacustrine origin; reclamation operations were car- ried out carefully following regular patterns. Under these circum- stances one would not expect abrupt lateral variation of the soil. At the Ir. A.P. Minderhoudhoeve, the Agricultural University's experimental farm in East Flevoland, however, thermal infrared imag- ery obtained in 1979, 1980, 1981 and 1982 showed consistent patterns for bare soil under drying conditions during Spring survey. The per- sistent, irregular patterns showed clear boundaries that could not be related to patterns of artificial drainage or management prac- tices; so it was thought that the differences seen on the imagery reflected differences in soil. This study attempted to determine the spatial distribution of soil properties and to find out which soil properties caused the pattern of thermal infrared imagery. A preliminary study had been done by Baltissen and Burrough (1982). Because the soil profile shows a marked stratification re- flecting the subsequent sedimentation phases, they studied strati- fication in detail. Soil texture was determined and crop data were studied. They concluded that a significant positive correlation existed between percentage coarse silt (16-50 ~m) in the topsoil and thermal infrared emittance, that stratification of the subsoil could not be related to emittance, and that possible differences in soil properties did not cause differences in crop yield for win- ter wheat (1979) and summer wheat (1981). Because the study of Baltissen and Burrough did not examine all physical properties of the topsoil with respect to the infrared patterns, one field was studied in more detail during Spring 1982. The aim of the 1982 experiments was to examine how spatial patterns of physical properties of the topsoil influence surface temperature, and might thus be detectable using thermal imagery. The experiments described here are part of a more extensive study on the behaviour of soil surface temperature and processes governing the energy bal- ance of bare soils. 0378-3774/83/$03.00 © 1983 Elsevier Science Publishers B.V.