LEACHATE ELECTRICAL-CONDUCTIVITY AND GROWTH OF POTTED GERANIUM WITH LEACHING FRACTIONS OF 0 TO 0.4

Geraniums (Pelargonium x hortorum L.H. Bailey 'Yours Truly') were grown in a glasshouse from 15 Mar. to 9 May as single pinched plants in a growing medium with a bulk volume of 1.3 liters per 15-cm diameter standard plastic pot. Plants received constant fertigation with N at 300 mg.liter-1 from 20N-4.4P-16.6K with leaching fractions (LFs) of almost-equal-to 0, 0.1, 0.2, and 0.4. The LF is the volume of solution leached from the container divided by the volume of solution applied to the container. There were 24 irrigations during the study. Plants with LFs of 0.2 and 0.4 had 46% larger leaf area, 40% more shoot fresh mass, and 37% more shoot dry mass than plants with LFs of 0 and 0.1. By week 5, the leachate electrical conductivity (EC) at 25C for LFs of 0.1, 0.2, and 0.4 had increased from almost-equal-to 3 dS.m-1 initially to 12, 8, and 4 dS.m-1, respectively. At harvest, the EC of a saturated medium extract (EC(e)) was 7, 4, 3, and 2 dS.m-1 for LFs of 0, 0.1, 0.2, and 0.4, respectively. At harvest, medium EC(e) with LFs of 0.1, 0.2, and 0.4 was 47%, 68%, and 60% less in the lower two-thirds of the pot than in the upper third. With a LF of 0, the medium EC(e) was not lower in the bottom of the pot. With fertigation N at 300 mg.liter-1, minimizing the LF substantially reduced growth of container-produced geraniums. In addition to specifying LF, the number of container capacities leached per week, termed the leaching intensity (LI), should be calculated for container leaching studies. In two studies, the LFs may be the same yet the LIs can be verv different.