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Plant Growth and Uptake of Nutrients as Influenced by Levels of Nitrogen¹

ABSTRACT

The growth and uptake of various nutrients by plants grown in nutrient cultures are reported. The correlations between root cation-exchange capacities and their nitrogen compositions for these crops were reported previously.

Plants grown under variable nitrogen levels produced increased top growth with higher nitrogen level. However, root growth generally did not increase in proportion to increased top growth with higher nitrogen level, and in some cases root growth was actually decreased. This necessarily meant increased top/root ratio with increased nitrogen level.

There was no systematic relationship between root cation-exchange capacity (or percent nitrogen) with the composition of Ca, Mg, P, K, and Na when various crops were grown in 1/5 Hoagland solution. This may not be unexpected in specific media devoid of competing colloids where Donnan effects are at a minimum.

With individual crop species grown in cultures of variable nitrogen levels, plants took up relatively more Ca and Mg with higher nitrogen level. The contents of P, K and Na were generally decreased with greater nitrogen content of the medium. This suggests that increased root cation exchange and its consequent Donnan effects had a regulating influence upon the uptake of the nutrients by the individual crops. Other factors affecting nutrient uptake are also discussed.

¹ Contribution from the Department of Agronomy, Ohio Agr. Exp. Sta. Preliminary stages of this study were completed at the Arkansas Agr. Exp. Sta.

² Associate Professor of Agronomy.

Received for publication July 20, 1956. Accepted for publication September 5, 1956.