563 Development of the Press Extraction Method for Plug Substrate Analysis: Quantitative Relationships Between Solution Extraction Techniques

Abstract

Methods for extracting growing substrate root-zone solution include the saturated media extract (SME) and the 2 water: 1 substrate (v/v) suspension, neither of which are particularly suited to bedding plant plug systems. We have developed the press extraction method (PEM) as a simple and quick alternative to these methods. The grower simply collects a representative sample of plug trays and presses the top of the plug, collecting the expelled solution. Solution pH and EC can be measured immediately and the sample then sent to an analytical laboratory for nutrient analysis. Initial experiments demonstrated that differing manual pressures did not affect solution chemical properties. The PEM then was compared to the SME and 2:1 methods over a range of fertilizer levels and with peat- and coir-based substrates. Within substrates, pH, EC, and macronutrients were similar between the PEM and the SME. The level of dilution inherent in the 2:1 method resulted in much lower EC and nutrient levels when compared to the other two methods. Further experiments compared the PEM to the SME and 2:1 on plug flats collected from several commercial greenhouses and also those grown in the research greenhouse. The wide range of bedding plant species and fertility levels tested introduced variation needed to develop regression equations and correlations to create quantitative interpretation ranges for the PEM based on previously published sufficiency ranges for the SME and 2:1.