CERAMIC AGGREGATE SORPTION AND DESORPTION CHEMISTRY: IMPLICATIONS FOR USE AS A COMPONENT OF SOILLESS MEDIA

Ceramic aggregates (Turface (R) and Profile (R)) are common soilless media components, but their sorption/desorption chemistry is poorly understood. We investigated: labile (readily desorb-able or readily plant-available) ion concentrations; the effect of rinsing and soaking pretreatments on labile ions; sorption of applied nutrients; and nutrient uptake from the aggregates by plants. Variability in labile ions was extremely high among bags of aggregates. Manganese, boron, magnesium, calcium, sulfur and potassium were most likely to desorb in excess for plants. Phosphorus, iron, copper and zinc were sorbed by the aggregates; only copper was found nearly deficient in plant tissue. Rinsing and soaking pretreatments adjusted labile ions to more suitable concentrations for plants. However, growth data suggested a worst-case scenario of high levels of labile ions may not be mitigated by these pretreatments. With frequent leaching after planting or where the aggregates are a minor component of media, excessive nutrient uptake would likely be limited.