Movement of 32P to roots of cabbage and lettuce grown in two soil types

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Abstract
Phosphate depletion zones around roots of cabbage and lettuce grown in two soils of differing phosphate sorption capacity were observed by autoradiography using P techniques. For both species 4–5 fold differences in the maximum depletion zone diameter were observed between krasnozem and podzolic soils; the krasnozem, with the higher phosphate sorption capacity, producing the smaller depletion zone diameter. Rate of radial spread of the depletion zones was used to determine the apparent phosphate diffusion coefficients (D values) and on this basis D values for the podzolic soil were 28–35 times those of the krasnozem. Within any one soil type there was little difference between species in the maximum diameter the depletion zone attained, however species differences in the rate of radial spread of the depletion zone resulted in cabbage having a greater D value than lettuce in each soil type. For plants in podzolic soil the depletion zones were equivalent to the diameter of the root hair cylinder, but plants in the krasnozem soil produced depletion zones only slightly greater than the root diameter although root diameters and root hair lengths were similar in both soil types.