Nitrogen Supply and Partitioning in Managed Understories of Organic Apples

Sustainable methods of nitrogen (N) fertility and weed management in organic production systems remain a challenge. Composted animal manures are commonly used to supply N, but only a fraction is in immediately available forms with the remainder released slowly as a result of microbial driven processes. These amendments come at a high cost, and excess application may result in salt damage, nutrient and profit loss, and environmental degradation. Systems are needed that will help reduce N fertility costs, mitigate N loss, and enhance availability at times corresponding with critical tree uptake periods. Intensive cultivation, a common management practice used to control weeds, can disrupt soil quality by degrading soil structure and accelerating nutrient cycling and organic matter loss. Alternative systems with reduced soil disturbance, such as organically approved herbicide or residues with natural herbicidal abilities, wood chip mulch, and maintenance of living cover crops, may help to ameliorate soil quality and alter soil fertility dynamics. Thus to address the needs of Washington organic orchardists for sustainable N fertility and weed management, an integrated study was established in spring 2005 to determine N-use efficiency and optimize fertility guidelines in these alternative systems.