A Note on Some Further Experiments Using Insoluble Dyestuffs for the Study of Soil Water Movement

Melinex' polyester film may be dyed by subliming insoluble dyestuffs to produce a permanent record of the distribution of dyestuff in a soil profile. Introduction In a recent paper (Clarke & Vincent, 1974), the authors described a method by which water movement in a soil column may be traced using harmless, insoluble dyestuffs which may be extracted and analysed quantitatively with relatively inexpensive apparatus. In order to obtain a picture of water movement in the soil column, discrete samples of soil must be analysed and the results contoured on a profile diagram. It was suggested, however, that it might be possible to obtain a record of water movement for the profile as a whole if 'Melinex'* polyester film was pressed against the soil surface and the whole heated until the dyestuff sublimes on to the film giving a permanently coloured picture of the flow of the dyestuff through the soil. In this note we describe an experiment which indicates that polyester film records of dyestuff concentration are relatively easy to obtain and are visually extremely satisfactory. Experimental methods Two wooden soil monoliths with external dimensions 400 mm x 160 mm x 90 mm were packed with Leighton Buzzard sand (86 % in the size range 500-250 ,um) and kaolin to a depth of 400 mm in the manner indicated in Fig. 1. The face of each monolith was covered by a sheet of plywood and the surface * A product of ICI Plastics Division.