USE OF RADIOACTIVE ⁵⁹ Fe FOR TRACING SOIL PARTICLE MOVEMENT

Abstract

Summary The field studies reported in Part 1 were complemented by laboratory investigations on the labelling of soils and the movement of soil particles by simulated rainfall splash. Of various labelling techniques tested the most uniform absorption of 59 Fe, as shown by autoradiographs, was secured by adding DTPA chelating reagent to the FeCl 3 solution used for wetting soil peds under vacuum. Studies on the specific radioactivity of the Atterberg textural fractions, separated from clayloam, sandy loam, loam and peat soils before and after labelling, showed in all cases that the clay fraction was dominant in retention of 59 Fe. The radioactivity was so firmly absorbed that its movement could be used to trace both the horizontal and vertical displacements of labelled soil particles by scintillation counting or autoradiographic techniques. Tests with a rainfall simulator showed a close correlation between the weights and radioactivities of splashed soil particles. Gravimetric data obtained from unlabelled clay loam and sandy loam soils subjected to ‘rainfall’ of differing intensity, drop size and height of fall gave a linear relationship on a logarithmic scale between mass of particles and distance of splash. Calculation of the kinetic energy lost by water drops on impact with the soil and that imparted to the splashed soil particles show that the relationship depends principally on the rainfall intensity and the texture of the soil.