Interpretation of soluble salts and pH of bulk solutions extracted by different methods

Y. Huang, L. Qu, C. A. Robinson, R. D. Caldwell


Soluble salts (SS) and pH are two easily measured parameters but critically important to the growth of containerized plants. Because different methods are being used for extracting bulk solutions from potting media, SS and pH readings for an identical medium may differ significantly. Until now a relationship had not been established that would allow the correlation of the metered results obtained from one extraction method to another. In this study, three commercial media were used to fill 15.1-cm (6-inch) pots and were fertilized with either a water-soluble fertilizer or a controlled-release fertilizer. Bulk solutions of the media were extracted three times using four commonly used methods: (1) pour through, (2) saturated media extraction, (3) 1:2 and (4) 1:5 (medium: water by volume) dilution. The initial bulk solution extractions were performed one week after golden pothos [Epipremnum aureum (Linden & Andre) Bunt.] were transplanted into the media; two additional extractions were conducted at two consecutive two-week intervals. The pH of the bulk solutions was not affected by the extraction methods, but SS readings were extraction-method dependent. Correlation coefficients of SS among the four methods were highly significant ranging from 0.62 to 0.84; thus, equations for converting SS readings from one extraction method to another were calculated.

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Proc. Fla. State Hort. Soc.     ISSN 0886-7283