The 2011 ASHS Annual Conference

The reduction of irrigation leachate would reduce resources and space required to store and/or treat leachate due to environmental concerns. In order to determine the affects of zero and near-zero leachate irrigation practices on irrigation volume, leaching fraction, water use efficiency (WUE) and crop growth of Zinnia ‘Profusion Knee High Red’ under greenhouse conditions and to determine how water status of Sunshine LB2 affects growth and development of this species, Zinnia seedlings were transplanted in December 2010 into 5 inch containers filled with a uniform mass of Sunshine LB2 substrate and placed on electronic scales in groups of four within a glass greenhouse. Substrate was brought to container capacity and the weight of the four container units (substrate + seedling - container) was recorded as the Effective Container Capacity (ECC). Irrigation was applied throughout the experiment so that the weight of the container units was maintained at 70%, 80%, 90%, or 100% of the weight recorded at ECC. At time of potting the estimated matric potential values were 2.78, 2.41, 2.03, or 1.64 kPa based on the substrate moisture release curve. Weight of the container units was allowed to drop 10% below the target weight before irrigating. A Microsoft Excel macro monitored container unit weight in real-time and controlled irrigation events. Irrigation was applied through pressure regulated drip emitters. Total water applied to each plant 8 weeks after initiation ranged from 2.08 L in the 70% ECC treatment to 4.14 L in the 100% ECC treatment. Water Application Efficiency (WAE; water used/water applied) increased linearly from 0.949 in the 100% treatment to 1.0 in the 70% treatment. WUE (g dry weight/L water used) was greatest among the 90% treatment at 3.54 g/L while least among 100% treatment at 2.75 g/L. Despite large differences in the total amount of water applied, regression analysis revealed no response in dry weights, leaf area, growth indexes, or flower number. Growth measurements were comparable to the control group, which had a WAE of only 0.731. Although plants in the 100% treatment were irrigated with 11.2% more water and produced 5.2 times more leachate, plants in the 90% treatment had the greatest growth index, shoot dry weight, leaf area, and flower number. EC ranged from 1.15 to 1.78 among treatments. Future research will determine if other commercial substrate mixes produce the same results when maintained at similar estimated matric potential values.