Leaching Fraction Effects On pH and Electrical Conductivity Measurements in Containers Obtained Using the Pour-through Method

Well-established protocols exist for using the pour-through extraction method to estimate substrate pH and electrical conductivity (EC) values for small root volumes. However, little work has been done to test the accuracy and consistency of these measurements in large containers. Our objective was to determine if the amount of distilled water applied to 1, 3, 5, and 10 gallon (2, 8, 11, and 27 L media volume, respectively) containers would affect leachate pH and EC values or consistency of measurements. Boxwood (Buxus × koreana ‘Green Velvet’) was selected for this study because it is a common container-grown nursery crop that does not alter pH in the root zone. Distilled water was poured evenly over the media surface in each container 1 h after irrigation to obtain a leachate volume of either 50 mL or 2.5% of media volume and leachate EC and pH were measured. Container size did not affect pH values. Media pH values were 0.1 – 0.3 points higher when 50 mL leachate was collected, but the difference was only significant during the first two weeks of measurements. There were no consistent differences in pH over container sizes or leaching fraction. Leachate EC values were similar when measured in leachate collected as 50 mL total volume or 2.5% of media volume in 8 and 11 L containers. However, in 27 L containers, obtaining 50 mL leachate resulted in higher EC values than when 2.5% media volume was obtained. Both pH and EC values obtained from 50 mL leachate fractions over container sizes were more consistent than when 2.5% of the media volume was collected. Growers should collect 50 mL of leachate to test media pH and EC, regardless of container size.