Effect of MES [2(N‐morpholino)ethanesulfonic acid] and amberlite IRC‐50 resin on nutrient pH control and soybean growth

Abstract

The relative effectiveness of Amberlite IRC‐50 resin, in a recirculating ion exchange column, and several concentrations of MES [2(N‐mor‐pholino)ethanesulfonic acid] were evaluated for control of nutrient solution pH of hydroponically cultured soybean (Glycine max [L.] Merr. cv Williams). A low buffering capacity, urea‐based nutrient solution was used. MES buffer, at the concentrations evaluated (1,2, 4, and 10 mM), was less effective at maintaining desired pH than the IRC‐50 resin system. The pH of the 4.0 mM MES buffered nutrient solution decreased from 6.5 to below 4.0 in five days with 25 to 30 day old plants. By comparison, the pH of the IRC‐50 resin buffered nutrient solution dropped from 6.5 to 5.9 during the same period. Nitrate uptake by 27 to 29 day‐old plants was significantly slower when solutions were buffered with MES than with IRC‐50 resin. Rate of nitrate uptake decreased with increasing MES buffer concentrations and decreasing pH in short‐term studies on plants previously grown on IRC‐50 resin buffered nutrient solution. Mass of the plants grown on IRC‐50 resin buffered nutrient solution equaled or exceeded that of plants grown on 1, 2, or 4 mM MES. Total elemental uptake (mg/plant) by plants grown on nutrient solution buffered by IRC‐50 resin, for the ten elements tested, was equal to or greater than uptake by plants grown on nutrient solution buffered by 1, 2, or 4 mM MES. It is concluded that IRC‐50 resin in recirculating columns provides better pH control than does MES buffer for hydroponically grown soybean.