RESPONSE OF PLANTS TO PHOSPHATE CONCENTRATION IN SOLUTION CULTURE

Abstract

Eight annual pasture spp. were grown for 4 weeks at constant phosphate concentrations ranging from 0.04 [mu][image] to 25 [mu][image]. At 0.04 [mu][image] all spp. showed symptoms of severe P deficiency, had low P contents, and, except for lupines which had large reserves of P in the seed, all grew very poorly. At 0.2 [mu][image] phosphate, all spp. made appreciable growth, and 2 of them reached 50% of maximum. This concentration corresponds to the lowest values in soil solutions extracted from productive soils, and is much lower than previously thought necessary for satisfactory growth in solution culture. Maximum growth of silver grass was reached at 1 [mu][image] phosphate compared with 25 [mu][image] for barrel medic and flatweed. Other spp. reached maximum yields at an intermediate concentration. Twenty-five [mu][image] phosphate produced severe leaf necroses in silver grass, clover, and lupines. The yield of silver grass was depressed to 66% of maximum. At 25 [mu][image], P concentrations in the tops of these 3 spp. ranged from 0.9 to 1.8% on a dry weight basis or 1.4-1.8 mg P/g fresh weight.