Assessment and Correction of the Alkalinity Problem Associated with Palabora Vermiculite1

Abstract

Palabora vermiculite having a pH of 9.8 was studied in order to (a) assess the extent of influence the alkaline reaction has upon several crops, and (b) to investigate further, means of correcting the problem where it exists. Four marigold, 3 zinnia, and 1 chrysanthemum cultivars were found to develop normally in this medium without adjustment of pH but the chrysanthemum cultivar ‘Giant Betsy Ross’, which is susceptible to alkaline reaction-induced micronutrient deficiencies, developed symptoms of Fe deficiency. Correction of this problem was accomplished in 2 ways: (a) by incorporation of sphagnum peat moss into the medium, and (b) by a drench with H₃PO₄ at the rate of 40 meq/100 g dry vermiculite.