INFLUENCE OF VARYING PHOSPHORUS SUPPLY ON THE GROWTH AND PHOSPHORUS COMPOSITION OF LETTUCE

The effect of varying phosphorus (P) supply on the growth, yield, leaf abnormalities, and nutrient composition was investigated for three le ttuce cultivars (Chaparal, Wintercrisp, and Robinvale) in sand culture and soil. The leaf P content for optimum yields varied between 0.40 a nd 0.90% while higher than 0.90% P seemed to cause leaf abnormalities in Chaparal and Winter-crisp. With high P supply, more calcium (Ca) wa s necessary to overcome the detrimental effect of P. In soil, maximum yields were obtained with a P supply level of 540 mg/kg P, while highe r levels caused yield reductions. Soil analysis at the end of the expe riment showed that a soil P content of 250 mg/kg P (Bray II) was assoc iated with the best yield. When additional Ca was supplied to the soil , yield reduction due to high P supply was reduced. The leaf abnormali ties which coincided with the high P supply were similar to those whic h have previously been described for auxin-type herbicide damage on le ttuce.