Estimating Nitrogen and Phosphorus Total Maximum Daily Loads for Container Nursery and Greenhouse Production Systems

In 1998, the state of Maryland adopted one of the toughest nutrient management planning laws in the United States, requiring that virtually all agricultural operations to write and implement nitrogen- (N) and phosphorus- (P) based management plans by December 31, 2002. Writing nutrient management plans for most ornamental nursery and greenhouse operations is a complicated task, since these operations grow a large number of plant species, and utilize a range of fertilization and irrigation strategies. A nutrient management planning process has been developed which combines water management (i.e. leaching fraction, interception efficiency and potential runoff) data with nutrient management (source and application rate) data into an estimate of total daily maximum loading (TMDL) rates. A risk assessment process based on operational management units identifies those site-specific factors that contribute most to nutrient leaching and runoff, and enables targeted best management practices to be developed to reduce the risk of N and P run-off into surface waters and the Chesapeake Bay. In association with this process, our research is examining interactions between irrigation and nutrient strategies with two model ornamental plant species that are widely grown in the nursery industry. Nitrogen and P applications, plant uptake and nutrient leaching are being continuously quantified to provide nutrient budgets over a three-year production cycle, to assess the effects of different management strategies on leaching and nutrient runoff potential. The development and use of new moisture-sensing technology, which can sense real-time water availability in soilless substrates will be necessary to provide more accurate irrigation scheduling and applications to nursery systems.