Use of Soil Health Indicators to Assess Long-Term Organic Management Effects on Cycling & Loss of Nutrients.

The Long-Term, Organic Farming Systems Research and Demonstration Site at Washington State University Puyallup Research and Extension Center is one of the few long-term vegetable production systems managed organically in the United States. The site was first certified USDA organic in 2004. The experiment focused on the intensive, organic vegetable crop production systems typical of experienced fresh market growers. The contrasting organic cropping systems provided us with a unique opportunity to study the effects of key management practices that included disturbance, amendment type, cover crops and livestock integration. The project evaluated short and long-term effects of different management systems on nutrient release, soil health, GHG emissions and ecosystem structure and function from 2003 to 2014. Our research illustrates the importance and potential to estimate the amount of plant available N provided by soil organic matter, animal amendments and cover crop residues as well as the need to synchronize release of inorganic N from these sources with N uptake in vegetable crops. Our research verifies that the organic N fertilizer regimes implemented maintained yield and improved soil health by increasing soil C stocks without contributing additional CO₂ emissions and by reducing or not contributing to reactive N losses i.e. NO₃^- leaching and N₂O emissions. In addition, we successfully used current and novel indicators of soil health to evaluate soil fertility and best management practices throughout a decade of organic systems management.