Effects of Compost Amendments on Soil Properties 14 Years after Application in a Virginia Coastal Plain Created Wetland.

In the past, constructed wetlands that are built to mitigate loss of natural wetlands have had issues such as low organic carbon and soil compaction. Organic matter (OM) amendments may help improve constructed wetland soil properties such as bulk density (BD), total carbon (TC), and total nitrogen (TN), but there are few studies that evaluate long term effects of OM amendments in constructed wetlands. This study was conducted to describe the effects of compost loading rates 14 years after application on soil properties. The experiment site is in the Virginia Coastal Plain and contains two separate experiment wetlands- CCW-Dry and CCW-Wet. The site was originally created by excavating 45-60 cm of surface soil to a silty E or clayey Bt or Btg horizon. Five different rates of yard waste compost were applied 2002 (treatment 1 = 0 Mg ha-1, treatment 2 = 56 Mg ha-1, treatment 3 = 112 Mg ha-1, treatment 4 = 224 Mg ha-1, and treatment 5 = 336 Mg ha-1 on a dry weight basis). In the fall of 2016, soil descriptions between 0-30 cm were made at each plot, and samples were analyzed for BD, TC, and TN. At CCW-Dry, A horizon soils in treatment 4 had significantly higher TC and TN than A horizons in the other treatments (p < 0.0001). At CCW-Wet, A horizons in treatment 5 had significantly higher TC (p=0.0042) and TN (p= 0.0025). There was a decrease in BD with increased compost at both wetlands, only in A horizons. The results suggest that in a compacted wetland soil, high amounts of OM amendments may only influence A horizons long term.