Storage procedures affect pH, electrical conductivity, and nutrient concentrations of pour-through leachate from pine bark and peat-based substrates

Authors: LANDAVERDE, ANDREA - THE OHIO STATE UNIVERSITY; Shreckhise, Jacob - Jake; Altland, James

Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/17/2020
Publication Date: 8/21/2020
Citation: Landaverde, A.C., Shreckhise, J.H., Altland, J.E. 2020. Storage procedures affect pH, electrical conductivity, and nutrient concentrations of pour-through leachate from pine bark and peat-based substrates. HortScience. 55(10):1597-1604. https://doi.org/10.21273/hortsci15232-20.
DOI: https://doi.org/10.21273/hortsci15232-20

Interpretive Summary: The pour-through (PT) method is used in greenhouse and nursery production to monitor nutrient availability in root media. Often, PT samples must be temporarily stored before being analyzed by the grower or shipped to a laboratory for analysis. Since many commonly measured parameters can fluctuate during storage, adequate preservation methods are necessary to ensure measured levels are representative of those in the root medium. However, evidence of how preservation methods change chemical characteristics of PT samples is limited. We evaluated the effect of storage time, storage temperature, and filtration of PT samples on pH, electrical conductivity (EC), and nutrient concentrations from pine bark (Experiment 1) and peat-based (Experiment 2) substrates. Samples were either filtered or non-filtered and then stored in plastic bottles at freezing, refrigeration or room temperature. Electrical conductivity, pH, and nutrient concentrations were analyzed at 0, 1, 7, and 30 days after PT sample collection. Electrical conductivity and pH in PT extracts of peat and pine bark, respectively, changed within 1 d of collection. Storage time had the greatest effect on nutrient concentrations of samples stored at room temperature. However, at 30 days, nutrient concentrations had also changed in samples stored at refrigeration and freezing. Measured parameters that changed the most in both experiments and across all preservation treatments were dissolved organic carbon (DOC), total dissolved nitrogen (TDN), NO3-N, and PO4-P, whereas Ca, Mg, and SO4-S were more stable in PT samples. Based on this research, we recommend that pH and EC be analyzed immediately after sample collection, whereas samples requiring nutrient analysis should be filtered immediately after collection, stored at refrigeration or freezing (preferably freezing), and analyzed within 7 days of collection.

Technical Abstract: The pour-through (PT) method is used in greenhouse and nursery production to monitor nutrient availability in soilless substrates. Efficacy of this method is based on the assumption that chemical properties of extracted solutions remain stable from the moment of collection until analysis. Extracted substrate solution can be analyzed directly in the greenhouse or sent to laboratories for complete nutritional analysis; thus, proper sample preservation methods (e.g., filtration and low temperatures) are critical for reducing sample contamination or degradation during storage. However, evidence of how these preservation methods affect chemical characteristics of PT samples is limited. The objective of this study was to evaluate the effect of storage time, storage temperature, and filtration of PT samples on pH, electrical conductivity (EC), and nutrient concentrations from pine bark- and peat-based substrates. Pour-through extracts were obtained from liquid-fertilized fallow pots of either 100% milled pine bark (Experiment 1) or a 4 sphagnum peat : 1 perlite (by volume) substrate (Experiment 2). Aliquots of PT extract were either filtered or non-filtered and then stored in plastic bottles at -22, 4, or 20 °C. Electrical conductivity, pH, and nutrient concentrations were analyzed at 0, 1, 7, and 30 days after PT sample collection. In both experiments, EC and pH changed at each sampling date, regardless of storage protocol. Storage time had the greatest effect on nutrient concentrations of samples stored at 20 °C. However, at 30 days, nutrient concentrations had also changed in samples stored at 4 and -22 °C. Analytes that fluctuated most in both experiments and across all preservation treatments were dissolved organic carbon (DOC), total dissolved nitrogen (TDN), NO3-N, and PO4-P, while Ca, Mg, and SO4-S were more stable in PT samples. In conclusion, EC and pH should be analyzed immediately, whereas samples requiring nutrient analysis should be filtered immediately after collection, stored at 4 or -22 °C (preferably -22 °C), and analyzed within 7 days of collection.