AN ANALYSIS OF THE GROWTH-RESPONSE OF CARROT SEEDLINGS TO DEFICIENCY IN SOME MINERAL NUTRIENTS

Critical plant concentrations for a reduction in relative growth rate to 90% of that of fully nourished plants were estimated by a novel met hod for several mineral nutrients. Carrot plants were grown from seed for 28 days in a range of nutrient solutions omitting N, P, K, Ca, S, Mg, Fe, B, Mn, Zn, Cu and Mo as separate treatments. All treatments ex cept -Mn, -Zn, -Cu and -Mo resulted in effects on plant growth and the development of deficiency symptoms. Estimates of critical concentrati ons were based on a simple simulation model incorporating the principl e of nutrient dilution with increasing plant weight and on mineral ana lysis of the plants. Parameters governing the shape of the relationshi p between fractional relative growth rate and plant nutrient concentra tion were altered until the model predicted the observed final mean dr y weight of deficient plants and time of divergence of this growth cur ve from that of fully nourished plants. Critical concentrations so obt ained were higher than those previously reported for Ca, Fe, N and P i n carrots and lower for K, Mg and S.