The 2011 ASHS Annual Conference

From 23 June through 16 October 2009 and 6 June through 31 October 2010, four conifer taxa were grown in 10.2-L (#3) containers and subjected to four irrigation regimes based either on daily water use (DWU) or a control application rate.  The plants grown were: 1) Chamaecyparis obtusa ‘Filicoides’, 2) Chamaecyparis pisifera ‘Sungold’, 3) Thuja occidentalis ‘Holmstrup’, and 4) Thuja plicata ‘Zebrina’.  The four irrigation treatments were: 1) control application of 19 mm^. container^-1.d^-1 2) irrigation applied to replace 100% DWU (100DWU), 3) applications alternating 100% DWU with 75% DWU in a 2-day cycle (100-75), and 4) a 3-day application cycle replacing 100% DWU on the first day and 75% DWU on the second and third days (100-75-75).  Irrigation treatments were applied every 24 h.  Irrigation volume, runoff volume, runoff nutrient content, and plant growth were monitored.  Irrigation treatments did not affect (P>0.05) plant growth index (GI=[height + width₁ + width₂] / 3) in 2009.  In 2010, GI of plants in the DWU treatments was equal to or greater than control plants for C. obtusa ‘Filicoides’.  Irrigation did not affect growth of plants from the other taxa in 2010.  Total water applied for 100DWU, 100-75, and 100-75-75 treatments was 22%, 32%, and 56% less, respectively, than the control of 117 L per container in 2009 and 24%, 18%, and 24% less than the control of 165 L per container in 2010.  Scheduling irrigation based on DWU reduced runoff volumes collected from growing areas and daily losses of NO₃^- -N and PO₄^3- -P when compared to the control.  In this study, irrigation was reduced in the DWU treatments which led to reduced runoff volumes and quantities of NO₃^- -N and PO₄^3- -P.