USING A CHELATE-BUFFERED NUTRIENT SOLUTION TO ESTABLISH THE CRITICAL SOLUTION ACTIVITY OF MN2-VULGARE L)( REQUIRED BY BARLEY (HORDEUM)

Relatively little is known about the responses of plants to micronutri ents when these nutrients are maintained at the very low levels found in soils of low fertility. We have determined the requirement of barle y (Hordeum vulgare L. cv Herta) for ionic Mn2+ in plant culture soluti ons using the chelating agent HEDTA as a buffer for micronutrient meta l ions. The chemical activity of Mn2+ was varied approximately 10,000- fold from log(Mn2+) = -10.8 to -6.8 (pMn 10.8 to pMn 6.8), while holdi ng constant the activities of the other micronutrient cations. Growth, appearance, and composition of 'Herta' barley indicated that log(Mn2) of approximately -8.3 would permit optimal dry matter production and normal plant development. The specific accumulation rate of Mn by 15 to 23 day old seedlings was a linear function of the Mn2+ activity in solution. At log(Mn2+) of about -9.8 or below, barley seedlings were u nable to accumulate significant amounts of Mn, and at some harvests, s uffered a net loss of Mn to solution. Seedlings younger than 11 days o ld were ineffective accumulators of several cations, including Mn, Fe, Zn, Cu, Mg, and Ca. Differences in Mn availability did not influence uptake of other cations, except that Cu uptake by roots increased with increasing Mn uptake.