A selection procedure for iron-deficiency stress tolerance among warm-season turfgrasses using ferrihydrite-amended growth media

Iron-deficiency (Fe-deficiency) stress, characterized by chlorosis of leaf tissue, is a major limiting factor in turfgrass production on calcareous soils. The objectives of this study were to: 1) evaluate ferrihydrite-amended growth media and the threshold amount of Fe initially added for use in a whole-plant screening procedure for selecting cultivars that are tolerant to Fe-deficiency stress conditions; 2) measure and evaluate whole-plant growth characteristics that could be an index of Fe deficiency stress; and 3) assess the potential of using a synthetically produced Fe oxide, ferrihydrite, as a slow-release Fe fertilizer source. Iron-stress sensitive 'Raleigh' St. Augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze] and Fe-stress tolerant 'Tifway' bermudagrass [Cynodon dactylon (L.) Pers, x C. transvaalensis Davy] cultivars were grown under glasshouse conditions in a medium consisting of quartz sand, 5% (m/m) CaCO3, and a ferrihydrite amendment providing Fe in concentrations of 0, 15, 30, 46, or 120 mg.kg(-1) media, (equivalent to 2, 3, 4, 5, or 10 mg DTPA-extractable Fe/kg media). There also was a nonlimiting iron control. St. Augustinegrass was first rated for iron chlorosis 83 days after planting (DAP) while bermudagrass was first rated at 294 DAP. Initial Fe levels equivalent to 5 mg DTPA-extractable Fe/kg media showed potential for screening genotypes. Visual estimates of iron chlorosis and chlorophyll contents of leaves were the best indicators of low soil Fe availability. A single ferrihydrite soil amendment at 10 mg DTPA-extractable Fe/kg media was adequate in preventing chlorosis for the duration of the study (174 and 509 days for St. Augustinegrass and bermudagrass, respectively). Chemical name used: Diethylenetriaminepentaacetic acid (DTPA).