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ASSESSING COMPOST MATURITY THROUGH GERMINATION TESTS AND NUTRIENT ANALYSIS**

Abstract

Composting is a process where organic waste is aerobically decomposed by microorganisms, with the goal of creating a soil amendment that promotes plant growth and reduces landfill waste. Georgia College operates a large in-vessel composter that recycles the dining hall’s food waste. The compost is then aged in large windrows to mature over one to two months. Though commonly a fertilizer, compost also has uses in green infrastructure, such as in amending bioswales and rain gardens which inhibit organic pollutants and heavy metals from leaching into natural waterways. However, it is important to make sure that compost is fully mature in its decomposition process before usage because immature compost can become a pollutant source if managed improperly. Poor management can lead to issues such as nutrient pollution and pathogen release. Immature compost can also cause a toxic response in plants, as chemical imbalances from excessive nutrients such as high ammonium and salt levels can stunt plant growth. This study evaluates the impact of compost at various maturity stages on the growth of a dicot lettuce species and a monocot grass species in a phytotoxicity germination test. Bioassays were conducted across various treatments: unamended sandy-loam soil (control), composts of various maturities (fresh from in-vessel through fully mature) and 1:1 ratios soil and compost mixtures of various maturities. Seeds were incubated for ten days, after which a standard seed germination index (GI) was used to assess potential toxicity and its effect on plant germination and root elongation. A GI less than 80% signifies growth inhibition and the presence of toxic compounds such as heavy metals and organic pollutants within the substrate. pH and plant nutrients including nitrate, ammonium, and phosphate were measured in each planting medium, and in each germination test’s watering leachate. These findings will help establish reliable compost maturity indicators to support effective and sustainable compost use.

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