Plant and Soil

, Volume 127, Issue 1, pp 129–136

Importance of the subsoil for the K nutrition of crops

  • H. Kuhlmann

DOI: 10.1007/BF00010845

Cite this article as:
Kuhlmann, H. Plant Soil (1990) 127: 129. doi:10.1007/BF00010845


A K/Rb isotope dilution method was used to determine the uptake of K from undisturbed subsoils. Rb was applied to the topsoil (0–30 cm) to trace the K taken up from the topsoil by crops. The K/Rb ratio in the crops increases when roots contact the Rb-free subsoil. This change in the K/Rb ratio enables the calculation of the uptake of K from the subsoil.

Results of 34 field experiments on loess-parabrown soils in N. Germany showed that the subsoil (>30 cm) supplied, on average, 34% of the total K uptake by spring wheat (range 9–70%).

The range between the experimental sites is considered in relation to the contents of K in the top and subsoils (as extracted by 0.025 N CaCl2 solution), the proportion of the total root length in the subsoils, and competition for K between roots in the top and subsoil.

In subsoils with similar K contents, uptake from the subsoil decreased significantly from 65 to 21% of total K uptake, as K contents in the topsoils increased from 4 to 8 mg K/100 g.

On sites with the same K contents in topsoils (9 mg K/100 g), the subsoil supplied 12 to 61% of total K uptake as the K contents of the subsoil increased from 2 to 27 mg K/100 g.

The contribution of uptake of K from the subsoil increased with the development of the crop, from 8% at first node stage to 35% at ear emergence, as the proportion of total root length in the subsoil increased.

High root length densities in the topsoil (9 cm/cm3) resulted in competition for K between roots and increased uptake of K from the subsoil.

Key words

K uptake spring wheat subsoil K/Rb ratio root density 

Copyright information

© Kluwer Academic Publishers 1990

Authors and Affiliations

  • H. Kuhlmann
    • 1
  1. 1.Centre for Plant Nutrition and Environmental ResearchDülmenFRG

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