EFFECTS OF SUBSTRATE POTASSIUM, SUBSTRATE TEMPERATURE AND LIGHT INTENSITY ON GROWTH AND UPTAKE OF MAJOR CATIONS BY GREENHOUSE TOMATO PLANTS

Abstract

Seedlings of the tomato Lycopersicon esculentum Mill. cv. Michigan-Ohio Hybrid were grown in perlite in plastic containers in a growth chamber. Maximum growth (dry weight and stem girth) was obtained under the higher substrate temperatures (24 C and 29 C) and the higher light intensity (16.2 × 10 3 lx) with an enhanced effect from high substrate potassium (12 meq K +/liter). Higher light intensity, coupled with higher potassium and higher substrate temperature, hastened maturity of the first flower buds. Total content of magnesium and calcium in the aerial portions of the plants was affected mainly by substrate temperature. Total content of potassium was, of course, influenced by potassium substrate levels as well as by substrate temperature. For all three cations, the content in plants grown at the lowest substrate temperature (13 C) was significantly lower than at the higher temperatures. However, when the uptake of these ions was expressed as percentage of dry weight, the differences due to substrate temperature disappeared, and differences due to light intensity and substrate potassium levels became evident.