Physicochemical Properties of Plant Growing Medium Comprising Water Treatment Residuals Amended with Composted Park

Abstract

The physicochemical properties were measured for medium comprising water treatment residuals (WTR) amended with composted bark (two different volume ratios of WTR to composted bark) one month after creation, in order to determine its suitability for plant growing purposes. Compared to the WTR alone, the WTR + bark medium exhibited similar neutral pH and a redox potential (Eh) indicating aerobic conditions, higher electrical conductivity (EC), cation exchange capacity (CEC), and total carbon (C) and nitrogen (N) concentrations, and lower phosphate (P) absorption coefficients and available manganese (Mn) concentrations. Comparing to the theoretical baseline medium immediately after creation, the WTR + bark medium, after a one-month incubation, exhibited a decline in available Mn, total C, and total N concentrations and an increase in CEC and P-absorption coefficients. These changes may be attributable not only to the introduction of composted bark but, also, to the increase in aerobic microbial activity or some factor by incubation. The pH, Eh, EC and C/N ratio for the WTR + bark medium indicated that it is suitable for growing plants. The reduction in available Mn concentration by nearly half relative to WTR alone suggests a lower occurrence of Mn toxicity syndrome for plants. Furthermore, despite the potential for the high P-absorption coefficient of WTR + bark medium to cause P deficiencies in plants, this deficit can be compensated by the application of P fertilizer. Thus, the WTR + bark medium is concluded to be suitable as a plant growing medium.