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Nutrient Cation Flows in Soil Around Plant Roots¹

ABSTRACT

The aim of the work was to test the relative importance of mass flow and diffusion in supplying nutrients to plant roots at different stages of growth, and whether there were, on average, important depletions or accumulations around the roots. Leeks (Allium porrum var. ‘Musselburgh’) were grown in large covered pots set in the field, and transpiration was measured by weighing. Nutrient content and root length were measured at four harvests, and soil solution composition was measured on 12 occasions. From this the mean inflows (uptake in moles/cm of root/sec) were calculated for K, Ca, Mg, and Na in three growth periods. They decreased strongly for sodium, slightly for potassium and magnesium, and remained constant for calcium.

The ‘apparent mass flow’ was taken as water inflow (ml/cm per sec) times soil solution concentration. It was small compared to total inflow for potassium, but increased with time; it was much larger than inflow for calcium, and slightly larger for magnesium and sodium.

The Passioura equation was used to calculate mean solution concentrations at the root surface. This indicated that the potassium concentration decreased to between 1/7 and of the original, but that of Ca, Mg, and Na was slightly increased on average. Root demand coefficients , are calculated from the results.

¹ Contribution from the Soil Science Lab., Dept. of Agricultural Science, Oxford University, England.

² Graduate Student and Lecturer, respectively, Dept. of Agr. Sci., Oxford University.

Received for publication June 25, 1969. Accepted for publication January 5, 1970.