Organic carbon and nitrogen stocks in a clay loam soil 10 years after a single compost application

Household food waste compost (FWC), yard waste compost (YWC) and pig manure plus wheat straw compost (PMC) were applied once in the fall of 1998 to a Brookston clay loam soil in southwestern Ontario to determine immediate and long-term effects of organic amendments on soil quality and productivity. In this report, we describe the residual effects of these single compost applications on soil organic carbon (SOC) and total soil nitrogen (TN) stocks 10 yr after compost addition (2009). FWC was applied at 75 Mg ha-1, 150 Mg ha-1 and 300 Mg ha-1, whileYWCandPMC were applied at the single rate of 75 Mg ha-1. The 75 Mg ha-1 additions of YWC, PMC and FWC increased SOC in the top 30 cm relative to a control (no compost additions) by 12.3% (9.0Mgha-1), 16.6% (12.2Mgha-1) and 0%, respectively; and they increasedTNrelative to the control by 8.0% (0.53Mgha-1), 11.7% (0.77Mgha-1), and 0%, respectively. The 150 and 300Mgha-1 additions ofFWCincreased SOC in the top 30 cm by 13.0 and 24.7 Mg ha-1, respectively, and they increased TN by 0.93 and 1.70 Mg ha-1, respectively. These results indicate that increases in SOC and TN stocks accruing from a single compost addition can persist for at least a decade, but the degree of increase depends strongly on compost type and addition rate. It was concluded that high compost addition rates of FWC and/ or addition of composts derived from recalcitrant organic materials may be a good strategy for achieving long-term carbon and nitrogen sequestration in the cool, humid fine-textured soils of southwestern Ontario.