Lime, Water Source, and Fertilizer Nitrogen Form Affect Medium pH and Nitrogen Accumulation and Uptake

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  • 1 Department of Horticulture, Michigan State University, East Lansing, MI 48824-1325

Hybrid impatiens (Impatiens wallerana Hook. F.) were planted into media containing two dolomitic liming materials {hydrated [Ca(OH)2 and Mg(OH)2] or carbonate (CaCO3 and MgCO3) lime} and subirrigated for 17 weeks with four irrigation water sources (IWS) and three water-soluble fertilizers (WSF). The WSF contained 200N–20P–200K mg·L-1 but varied in NH4+-N content (50%, 25%, or 3%, respectively). Depending on the IWS and lime type used in the media, root-medium pH ranged from 4.5 to 6.0, 4.8 to 7.1, and 6.0 to 8.5 when treated with WSF containing either 50%, 25%, or 3% NH4+-N, respectively, between 8 and 17 weeks after planting. The accumulation of NH4+-N and NO3--N in the root medium was different for treatments receiving the same WSF and depended on root-medium pH. The critical root-medium pH for NH4+-N accumulation was between 5.4 and 5.7, and for NO3--N, accumulation was between 5.3 to 5.9. Above this pH, minimal NH4+-N concentrations were measured in the medium, even with 50% or 25% NH4+-N WSF, while below this pH, NH4+-N began to accumulate in the medium with a corresponding decrease in the NO3--N concentration. The NH4-N: NO3-N ratios in the WSF had minimal effect on shoot fresh and dry weights. Tissue N concentration was higher with the higher NH4-N : NO3-N ratio WSF at all four sampling dates. There was a linear relationship between higher tissue N and lower root-medium pH with the same WSF, possibly due to differences in the ratio of NH4-N: NO3-N actually taken up by the plant.

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