Studies in the nutrition of vegetables: Phosphate deficiency and yield tests on sand cultures of May King lettuce

Extract

Media from which phosphate was absent finally caused bronzing of the leaves of the resulting stunted plants of May King lettuce grown in sand culture, and red or crimson stalks. Phosphate alone produced characteristic purple (and/or bronze) and apple-green, flat, stunted rosettes with broad, non-crinkly leaves, and red stalks. Water alone caused stunted, straggly, purple plants, with relatively long, crimson stalks.

Where some phosphate was supplied in addition to the other essential elements, a plant of normal colour resulted at first. Later, purple blotches appeared on the plants receiving inadequate supplies; the intensity of this purple became greater as the amount of phosphate in the medium diminished, and it could be controlled by varying the concentration of phosphate in the medium or the frequency of application. Another deficiency symptom was the tougher leaf resulting from a lack of phosphate. A sufficiency of phosphate caused earlier maturity.

The media which contained the two greatest concentrations of phosphate were the best of those used because they gave the best growth, lettuces of the best colour without purple blotches, earlier maturity, and tenderer leaves.

The final yields of heads were statistically the same with the two heaviest phosphate treatments, and both were greater by about 40% of the lesser yields than the two statistically equal yields with the lower amounts of phosphate. All the phosphate treatments gave yields superior by about 40,000–60,000% to the non-phosphate and phosphatealone yields, but this second difference had no commercial significance. Similar results were obtained for the roots, and for the dry weights of the tops and roots.