For many dairies, more nutrients are imported in feed than are exported in milk. Only about 1/4 to 1/3 of the nitrogen and phosphorus a cow consumes is captured in milk. Over time this has resulted in an excess of nitrogen and phosphorus in soil.
Excess nitrogen (nitrate-nitrogen) in soil that is not utilized by crops can be lost below the root zone and move to groundwater. Soil has a greater capacity to store phosphorus compared to nitrate-nitrogen, but when that capacity is saturated, phosphorus can be released to ground and surface water.
Excess nitrogen and phosphorus cause eutrophication or nutrient enrichment of water bodies. Nutrient-enriched water can cause excess algae growth and result in reduced levels of oxygen in water, negatively impacting aquatic animals.
Forages play the central role in whole-farm nutrient management. Whatever can be done to maximize home-grown forage production will decrease the need to import nutrients from off-farm and decrease the risk of nutrient loss via air or water.
On a typical Northwest dairy, an acre of corn silage will process the nutrients from approximately 25,000 to 30,000 gallons of manure and utilize 250 pounds of nitrogen, 40 pounds of phosphorus and 240 pounds of potassium.
Grass silage will process the nutrients from around 30,000 to 40,000 gallons of manure and utilize 350 pounds of nitrogen, 60 pounds of phosphorus and 340 pounds of potassium. Alfalfa can process similar amounts of nutrients to grass, but due to its ability to fix nitrogen and the negative effects of high manure applications to alfalfa, alfalfa needs to get 50 percent or more of its nitrogen from the atmosphere.
Paying close attention to a number of key factors related to feed and forage management can markedly reduce the amount of nutrients imported to the farm in feeds such as hay, grains and byproduct feeds. In addition, the adoption of these practices will also improve profitability.
• Select a ratio of corn-to-grass or alfalfa that will minimize import of nitrogen to the farm
• Manage your crops for high forage yields
• Harvest grass, corn or alfalfa at its prime digestibility
• Use relay-crop and multi-crop practices when possible
• Use a proven silage additive to promote a good fermentation in the silo
• Pack the silage well to minimize loss of dry matter and digestibility, as well as minimize the opportunity for the growth of yeasts and molds
• Mechanically process your corn silage to enhance fiber and starch digestibility
• Formulate diets for the needs of rumen-degradable and undegradable protein, and consider the use of rumen-bypass lysine and methionine to decrease imports of nitrogen to the farm
• Use minimum tillage practices if soil and climate conditions allow, thus minimizing the loss of soil nitrate-nitrogen to shallow groundwater
• Consider relay or double cropping to utilize more nutrients from manure
• Use annual soil testing to adjust manure applications
• Apply manure with subsurface deposition, injection or incorporate as soon after application as is practical to avoid loss of volatile nitrogen
• Use routine manure tests to match application rates with crop needs
• Avoid use of commercial fertilizer when re-seeding grass fields as tilled sod will provide adequate amounts of nitrate-nitrogen
• Use milk urea nitrogen as a tool to monitor efficiency of diet nitrogen for milk protein production
• Monitor the efficiency of milk production by monitoring the ratio of milk production to dry matter intake
• Routinely run dry matters on silages and calculate dry matter intake
• Group animals by nutrient needs (low versus high production)
A new program is available from the USDA Natural Resources Conservation Service (USDA-NRCS) that will provide financial assistance to livestock and poultry producers to systematically develop a feed management plan. Feed management plans are similar to nutrient management or crop-nutrient plans, but focus on the feed practices on the farm. ANM
Joe Harrison
Nutrient Management Specialist at Washington State University
This article originally ran in an issue of Ag Nutrient Management.
