Kinetic Assessment of the Biodegradability of Gel-Forming Soil Conditioners in Incubation Experiments with Instrumental Monitoring of Carbon Dioxide

Abstract

A quantitative study of the biodegradability of polymer soil conditioners is necessary for a reasonable prediction of their stability and functioning in soils. For this purpose, we proposed a new methodological approach based on PASCO (USA) equipment, which allows recording continuous kinetic curves of CO2 emission in laboratory experiments on incubation of composite gel-forming soil conditioners. Several characteristic types of respiratory curves have been identified and new physically based models have been proposed for their description with subsequent calculation of the half-lives of composite hydrogels. For the traditionally considered non-biodegradable acrylic superabsorbents of soil water, the possibility of rapid biodegradation was shown for the first time in the case of the introduction of a biologically active compost extract into their liquid phase. With this treatment, which brings laboratory experiments closer to real soil conditions, the half-lives of both the well-known Western superabsorbents Aquasorb and Zeba and the Russian hydrogels Aquapastus decreased by an order of magnitude from the initial values of 2–6 years to 0.1–0.3 years. In practice, this can negatively affect the profitability of using such materials for soil conditioning due to their rapid destruction and loss of functionality. The introduction of silver ions into innovative Aquapastus composite superabsorbents at a dose of 0.1% or 10 ppm in swollen gel structures effectively reduces their biodegradability, prolonging the half-life to 10 years or more, which is twice the German standard DüMV 05.12.12 for the stability of polymer meliorants.