The Effect of Lime, Irrigation-water Source, and Water-soluble Fertilizer on Root-zone pH, Electrical Conductivity, and Macronutrient Management of Container Root Media with Impatiens

Abstract

Hybrid impatiens ( Impatiens Wallerana Hook. F.) were planted in a peat-based medium containing two dolomitic liming materials (1.8 kg Ca(OH) 2 ·Mg(OH) 2 /m 3 or 8.4 kg CaCO 3 ·MgCO 3 /m 3 ) and subirrigated for 17 weeks using four irrigation-water sources (IWSs) with varied bicarbonate alkalinity, Ca 2+ , Mg 2+ , and SO 4 -S content and three water-soluble fertilizers (WSFs) that contained (in mg) 200N-20P-200K/liter but a variable NH 4 : NO 3 ratio, Ca 2+ , Mg 2+ , and SO 4 -S content. The factorial arrangement of the IWS and WSF resulted in a range of Ca 2+ , Mg 2+ , and SO 4 -S concentrations varying by a factor of 10. After 8 weeks, medium pH ranged from 4.5 to 8.5. The maximum critical medium pH for PO 4 -P uptake was 7.4 to 7.7, which probably was due to a change in most of the water-soluble P to the less-available HPO 4 2- form. Lime type did not affect the long-term increase in medium pH, Ca 2+ , and Mg 2+ concentrations with nutrient solutions containing low NH 4 + -N and high Ca 2+ and Mg 2+ . The carbonate lime buffered the medium pH and Ca 2+ and Mg 2+ concentrations with nutrient solutions containing high NH 4 + -N and low Ca 2+ and Mg 2+ compared to that measured with the hydrated lime. With both lime types, there was a linear increase in tissue Ca and Mg as the applied concentrations of the various nutrient solutions increased from 18 to 210 mg Ca 2+ /liter and 7 to 90 mg Mg 2+ /liter. The relationship was similar for both lime types up to week 8, after which tissue Ca and Mg decreased more rapidly with the hydrated lime and low solution Ca 2+ and Mg 2+ compared to that of the same carbonate lime treatments. The minimum critical SO 4 -S concentration in the applied nutrient solution for plant uptake was 30 to 40 mg S/liter. Below this concentration, tissue S decreased rapidly; above, there was little effect on tissue S.