According to the Oregon Department of Agriculture, greenhouse and nursery crops are Oregon’s #1 agricultural commodity, using over 50,000 acres of agricultural land. Of these greenhouse and nursery crops, container grown plants are the highest selling crop with the greatest gains, increasing 12% from 2005 to 2006. Forty-four percent of nursery product sales come from container products.
The majority of container growers use predominantly organic substrates amended with controlled release fertilizers to maximize plant growth. This results in available nutrients for plant uptake that are also susceptible to leaching and runoff. Nutrient availability from controlled release fertilizers is directly linked to temperature. Increased temperature results in increased nutrient release. A popular perception is that with cooler temperatures, little or no nutrients are released from controlled release fertilizers and that water can leave the nursery site without degrading off-site water quality. However, current research in the southeast and California has shown that controlled release fertilizers continue to release nutrients throughout the winter months when average temperatures are above 40°F. Therefore, container leachates may contain high nutrient concentrations exceeding maximum contamination concentration and daily load standards established by the United States Environmental Protection Agency.
In order to assess the potential environmental impact of fertilizer leaching in container nurseries through the winter season, Dr. Jim Owen and Heather Stoven, in cooperation with USDA-ARS, are currently conducting research at the Oregon State University North Willamette Research and Extension Center in Aurora, OR. A runoff pad was constructed that allows for the collection of leachate from replicated simulated container nurseries. The runoff from the container facility is collected in tanks from which samples are collected and analyzed for macro and micro-nutrient mineral nutrient content. Ambient weather data along with soilless substrate temperature are being collected to measure the relationship between temperature and fertilizer release. At the end of this winter the plants, substrate, and remaining controlled release fertilizer will be harvested and analyzed to determine mineral nutrient budgets that will account for plant nutrient uptake, substrate nutrient retention, fertilizer release, and ultimately runoff nutrient content and concentration.
This study will allow nurseries to assess their environmental impact in terms of water quality. Also, new information will be available to growers about plant mineral nutrient uptake and release of fertilizer during winter months in the Pacific Northwest. The information may lead to greater use efficiency for commonly used controlled release fertilizers.