The transport of potassium to ryegrass roots in soils with and without added potassium

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Abstract
SUMMARY The mechanisms responsible for moving K from soil to root were studied by growing perennial ryegrass in pots containing a flinty silt loam from Rothamsted and a sandy Woburn soil, with and without added K, at 0.75 water-holding capacity. More water was taken up from the Rothamsted soil than from the Woburn soil, and less was taken up when K was added without affecting dry-matter production. After 25, 52, 83, 122, 194 and 276 days, K uptake, water uptake and the K concentration in the soil solution were measured and the mass-flow contributionto K uptake calculated. Without added K, mass-flow accounted for only about one-sixth of the K taken up from the Rothamsted soil and about one-third from the Woburn soil. Except at first, diffusion probably accounted for the remainder of uptake but was the rate-controlling step for uptake from the Woburn soil only. With added K, mass-flow became much more important relative to diffusion in both soils, and transported more than enough K to account for the measured K uptake. Root interception probably did not contribute to K uptake after the early part of the experiment, because the pots used were small.
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