ARS | Publication request: Root substrate testing with the Rhizon Soil Moisture Sampler

Submitted to: Greenhouse Product News
Publication Type: Trade Journal
Publication Acceptance Date: December 5, 2010
Publication Date: February 1, 2011
Citation: Nelson, P., Jeong, K., Frantz, J. 2011. Root substrate testing with the Rhizon Soil Moisture Sampler. Greenhouse Product News. Feb 2011.

Technical Abstract: Three common methods are used for extracting solution from greenhouse root substrate for testing pH, EC and nutrient levels: the saturated media extract procedure, the 2:1 extract, and the PourThru. Each has strengths and weaknesses requiring knowledge of each in selecting an approach to match the needs for your production system. The Rhizon Soil Moisture Sampler (RS) is a more recent system that offers a fourth means for extracting substrate solution. It is a rigid, porous plastic extraction tube that is inserted into the substrate, and solution is extracted under vacuum through a rubber cap on a collection vial. As the handle of the pump is repeatedly squeezed by hand, a vacuum is created in the system that draws substrate solution into the rigid extraction tube and then on into the sample vial where it is trapped. We evaluated the effectiveness of the RS and compared it to the PourThru approach. We grew crops of lettuce in peat-based substrate and fertilized these with a complete, neutral fertilizer. When roots completely filled the pot, sampling comparisons were begun and were repeated at three intervals. Results showed that the RS samples represented the substrate solution from the immediate vicinity in which they were placed, and when installed vertically, a greater proportion of solution from the bottom of the pot was sampled than the top. The PourThru method has the same bias, so standards already developed for that method should work well with the RS method. Overall, the two approaches complimented one another; the new method allows for growers to sample their root zones in more specific ways than they otherwise would be able to do with only the PourThru approach.