Methods for Controlling pH in Hydroponic Culture of Winter Wheat Forage

Abstract

Abstract Plants grown in hydroponic culture make useful experimental models for soil‐grown plants. However, a major problem of nutrient solution culture is the adequate buffering of solution pH. Four methods of controlling pH in hydroponic culture of winter wheat ( Triticum aestivum L. ‘Centurk’) were compared at two levels of Ca (0.2 and 2.0 m M ) to determine the buffering method with the least effect on the uptake of essential nutrient elements. These methods were: (i) manual titration with NaOH; (ii) Amberlite DP‐1 weakly acidic cation exchange resin loaded with Ca, Mg, K, and H; (iii) the organic buffer, 2‐(N‐morpholino)ethanesulfonic acid (MES), at 1m M ; and (iv) MES a t 5 m M . Five‐millimolar MES gave the most consistent control of solution pH. However, it also inhibited Zn accumulation by wheat. One‐millimolar MES did not maintain the solution pH as well as 5 m M MES, but it did not significantly alter the uptake of any essential nutrient element. It is recommended as a pH buffer for the hydroponic culture of winter wheat. Resin in membrane bags did not adequately buffer the solution pH. It also removed some Mn and Zn from solution, thus depressing their uptake by wheat. Resin in a pump system adequately buffered the solution pH until its effectiveness was limited by the flow rate through the resin bed. Adequate buffering of solution pH was found to be critical for experiments that study the interactions between Ca and other nutrient elements. With the pH buffer, MES, the previously reported effects of Ca on depressing Mg, Mn, and Zn accumulation were observed. However, in the poorly buffered treatments, these elements tended to increase slightly with increasing Ca levels, perhaps due to the effect of Ca on maintaining root membrane integrity in an acidic environment.