Recycling of Nitrogen through Land Application of Agricultural, Municipal, and Industrial By-products.

The development of beneficial, environmentally sound approaches to use agricultural, municipal, and industrial by-products in agricultural production systems is of more importance today than ever before because alternatives to land application are increasingly limited. Fortunately, we have the knowledge needed to conduct science-based assessments of the factors that determine whether by-products are suitable for agricultural use. We also have the practical experiences needed to implement, manage, and monitor land application programs that maximize the beneficial use and minimize the environmental impacts of by-products. Having said this, it must be recognized that considerable concern and outright opposition exists to the application of many by-products to agricultural lands. Most concerns stem from: (i) uncertainty about the long-term fate and transport of by-product constituents, particularly those which may affect environmental quality or human health; and (ii) skepticism about how well by-products are characterized, stored, handled, and applied; essentially fears that economic constraints or mismanagement will result in poorly implemented land application programs that degrade the environment or threaten human health. Therefore, to be effective, any land application program for by-products must integrate scientific principles and management and monitoring programs with many social, political, and regulatory constraints. This presentation addresses a key aspect of the beneficial agricultural use of by-products - the potential to recycle by-product N by application to crop land and other managed agricultural systems (e.g., forests, horticultural settings). We focus on by-products that (i) are used primarily as N sources, thus we seek to manage N to optimize plant growth and protect the environment; or (ii) affect N cycling and availability because of other by-product properties (e.g., C/N ratio, metals, salts).