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<p> </p> <p>NUTRIENT MANAGEMENT, particularly manure management on dairies, has been a focus of legislation in Washington State over the past decade. After several unsuccessful attempts in the early 1990s to encourage dairy producers to voluntary adopt practices to prevent manure from negatively affecting water quality, the Dairy Nutrient Management Act (RCW 90.64) was promulgated in 1998. Passage of the act was influenced by the partial closure of Portage Bay shellfish beds on the Lummi Indian Reservation in 1996 (<a href="http://www.biology-online.org/articles/references-manure_management_effects_on_grass_production_nutritive_content_and_soil_nitrogen_for_a_grass_silagebased_dairy_farm.htm#BIB4">Boggs et al., 2002</a>). Both surface and ground waters are regulated resources in Washington State. </p> <p>The Dairy Nutrient Management Act required producers to develop approved nutrient management plans by July 2002, and have the plans certified as fully implemented by December 2003. Dairies that qualify as concentrated animal feeding operations (CAFO) are required to have a nutrient management plan that addresses N and phosphorus by December 2006. The practices used in the nutrient management plans were to meet the standards, specifications, and methods described in the USDA Natural Resources Conservation Service (NRCS) <em>Field Office Technical Guide</em> (<a href="http://www.biology-online.org/articles/references-manure_management_effects_on_grass_production_nutritive_content_and_soil_nitrogen_for_a_grass_silagebased_dairy_farm.htm#BIB19">USDA, 2004</a>). One conservation practice standard that serves as the major basis of the Nutrient Management Plan is NRCS Nutrient Management 590. In Washington State, the 590 standard requires a fall soil test for nitrate evaluation (<a href="http://www.biology-online.org/articles/references-manure_management_effects_on_grass_production_nutritive_content_and_soil_nitrogen_for_a_grass_silagebased_dairy_farm.htm#BIB17">Sullivan, 1994</a>). The fall soil nitrate test is intended to provide an evaluation of the past season's N management, rather than to predict how much fertilizer is required the next spring. </p> <p>The concept of a nutrient management plan was new for many dairy producers, as was the practice of taking soil samples in the fall to evaluate N management during the previous growing season. Producers and their advisors needed education about the value of the management plans and how to correctly implement the fall soil sampling. The requirement provided an opportunity to evaluate the interrelationship of N behavior in the manure, plant, and soil system on a dairy farm in western Washington. The goal of this project was to evaluate years of farm data from five grass fields. On-farm research studies have improved the understanding of nutrient management at the farm or larger scale and the effect of this management on the environment (<a href="http://www.biology-online.org/articles/references-manure_management_effects_on_grass_production_nutritive_content_and_soil_nitrogen_for_a_grass_silagebased_dairy_farm.htm#BIB3">Bacon et al., 1990</a>; <a href="http://www.biology-online.org/articles/references-manure_management_effects_on_grass_production_nutritive_content_and_soil_nitrogen_for_a_grass_silagebased_dairy_farm.htm#BIB10">Harter et al., 2002</a>; <a href="http://www.biology-online.org/articles/references-manure_management_effects_on_grass_production_nutritive_content_and_soil_nitrogen_for_a_grass_silagebased_dairy_farm.htm#BIB11">Hutson et al., 1998</a>; <a href="http://www.biology-online.org/articles/references-manure_management_effects_on_grass_production_nutritive_content_and_soil_nitrogen_for_a_grass_silagebased_dairy_farm.htm#BIB13">Klausner et al., 1998</a>; <a href="http://www.biology-online.org/articles/references-manure_management_effects_on_grass_production_nutritive_content_and_soil_nitrogen_for_a_grass_silagebased_dairy_farm.htm#BIB21">Wang et al., 1999</a>). </p> <p>A uniqueness of our evaluation is the focus on temporal relationships at 4-wk or lesser intervals to characterize the N behavior among manure, soil, and forage systems. The multiyear evaluation of N management, with the goal of more precisely managing N application for grass production, began in 2001. Historical forage quality information from this farm indicated that an opportunity existed to achieve higher levels of crude protein (CP) in grass silage, thus decreasing on-farm import of N. </p> <p>The primary specific objective was to determine the effects of liquid manure applications on the CP and nitrate content of grass silage. A secondary objective was to determine the effects of additional manure application on soil nitrate concentrations as affected by the time of soil sample collection throughout the year with an emphasis on the fall period. </p>
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