Growth and Mineral Composition of Vegetable Seedlings

Abstract

Seedlings of eight species of vegetables were grown in John Innes seed compost. Differences between the mean dry weights of seedlings of the different species shortly after emergence were directly related to differences in mean seed size between species; differences in mineral composition, however, were much greater for the seedlings than for the seeds. Chemical analysis of seedlings of cabbage, lettuce, onion and carrot grown in sand culture confirmed this finding.In sand culture, the dry weight per seedling increased as the K+ concentration in the nutrient medium increased from zero to 8−0 m.equiv.K+/l. although for cabbage and onion the increase was small over the range of 3-5 to 8−0 m.equiv.K+/l. The % K in the dry matter of the seedlings increased with increasing concentration of K+ in the nutrient medium. Both these effects were apparent 3 days after emergence of the seedlings.At about 20 days after emergence, seedlings of lettuce, onion and carrot grown in John Innes compost were smaller and had a lower % potassium content than those grown in sand culture at a K+ concentration of 8−0 or 3−5 m.equiv.K+/l. Cabbage seedlings grown in compost and in sand at the 3−5 m.equiv.K+/l. level were similar in size and composition. It is concluded that seedlings of lettuce, onion and carrot did not take up sufficient amounts of potassium from John Innes compost to sustain optimal growth.