Journal zyxwvutsrqp of Soil Science, zyxwvutsr 1985,36,141-152 zyxwvutsr Complementary use of thermal imagery and spectral analysis of soil properties and wheat yields to reveal cyclic patterns in the Flevopolders P. A. BURROUGH,* zyxwvu A. K. BREGTt zyxw & M. J. DE HEUS Department of Soil Science and Geology, Agricultural University, Wageningen, and E. G. KLOOSTERMAN Ir. A. P. Minderhoudhoeve Experimental Farm, Agricultural University at Swijterbant, The Netherlands SUMMARY The Flevopolders in the north-west of The Netherlands are located on recently reclaimed, uniform, flat alluvial soils. Strong contrasts in soil were thought to be unlikely. Yet thermal imagery of experimental fields carried out over zyx 4 years revealed the presence of a striped pattern with a regular wavelength of 24m. This was remarkable considering that drainage had been carried out at a 12m spacing. Crop yields, topo- graphic heights, tensiometer data, penetrometer readings and soil profiles also indicated the presence of a 24 m ‘wave’. Investigations into the land reclamation procedures carried out 20 years ago finally revealed the cause. The implications for management are discussed. INTRODUCTION The Flevopolders in the north-west of The Netherlands are renowned for the large area of flat land with apparently uniform soil that provides excellent conditions for arable farming. Because these recently reclaimed polders are so flat, and the sedimentary processes that gave rise to them were so uniform (Pons & Wiggers, 1959), abrupt short-range changes in the soil that could lead to vari- ations in the response of agricultural crops are unexpected. Yet yield variations in wheat uniform- ity trials conducted over 4 years at the Agricultural University’s Ir. A. P. Minderhoudhoeve Experimental Farm near Swifterbant (Fig. 1) suggested that there was a regular 24 m pattern in the soil. Investigations in early spring with air-borne thermal infra-red scanners have also revealed regular 24 m-spaced striped patterns across bare fields on the experimental farm and neighbouring areas, though the pattern had not been detected in other experimental farms in the Flevopolders (Burrough, 198 I). So soil investigations were carried out to attempt to determine the source of the stripe pattern, its possible cause and its implications for using the farm for agricultural trials. The experimental farm is located on land that was reclaimed only 25 years ago (Lambert, 197 1). Following normal methods of regional drainage and improvement after empoldering, the area of the farm and its immediate surroundings were drained in 1960 by a series of ‘greppels’ or shallow drainage ditches. These ditches were made with a special plough that cut a furrow 60 cm wide and 50 cm deep. These ditches were accurately located on a 12 m spacing. Later, in 1963, the ditches were filled in, and tile drains were put in at the same places at a depth of 110-130cm, preserving the 12 m spacing. Any remaining surface irregularities were removed by levelling opera- tions in 1963. The land was transferred to the Agricultural University in 1968. It was not at all * Present address: Vakgroep Fysische Geografie, Geografisch Instituut, Rijksuniversiteit Utrecht, The t The Netherlands Soil Survey Institute, Wageningen. Netherlands. 141