Iron Chlorosis in Gerber as Related to Properties of Various Types of Compost used as Growing Media

Abstract

Nutrient deficiencies in crop plants may be influenced by a number of properties of the growing media. Some peat‐substitute substrates can promote iron (Fe) chlorosis in sensitive plants, which has traditionally been ascribed to the elevated pH of growing media. To identify the origin of this problem in various types of composted organic residues used as growing media and possible corrections, a complete randomized experiment on gerber (Gerbera jamesonii Adlam) as an Fe‐chlorosis sensitive crop involving three factors (growing medium, medium acidification, and the medium treatment with Fe) was performed. Although the Fe content in plants decreased with increasing pH in the growing medium, the chlorophyll content as measured using a chlorophyll meter (Minolta Soil Plant Analysis Development, SPAD) was not significantly related to pH. The SPAD readings and Fe concentrations in plants, dry matter, and flower production were not significantly related to diethylenetriaminepentaacetic acid (DTPA)–extractable Fe in the growing media. The addition of Fe‐chelate significantly increased yield (P<0.01), and SPAD at 65 and 96 days after planting (P<0.001 and P<0.01, respectively). However, the effect of the acid treatment was, different depending on the growing media. When the acidification promoted a positive effect on SPAD readings, this was nonsignificantly different than that obtained with the application of Fe‐chelate. The estimated amount of available Fe in the growing media was not relevant, which explains the incidence of chlorosis as physiological factors related to pH.