Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 16, 2009
Publication Date: June 1, 2009
Citation: Powell, J.M., Grabber, J.H. 2009. Dietary Forage Impacts on Dairy Slurry N Availability to Corn. Agronomy Journal. 101:747-753. Interpretive Summary: Much of our research at the U.S. Dairy Forage Research Center is an effort to produce forages in which the protein is used more efficiently by the dairy cattle that eat them. If more protein is used by the animal, less nitrogen is excreted in the manure (urine and feces). Because manure applied to the land is a valuable fertilizer for crops, we conducted a study to determine if the type of forage fed to dairy cattle changes the manure chemistry in a way that affects the availability of the nitrogen from the soil. We fed dairy cattle four types of silages: alfalfa, red clover, low-tannin birdsfoot trefoil, or high-tannin birdsfoot trefoil. When the manure from these cattle was applied to the land, we found that manure type only periodically affected the concentration of plant available nitrogen in the soils. Corn nitrogen uptake after spring application of manure from cows fed alfalfa silage was greater than corn nitrogen uptake in plots amended with manure from cows fed low-tannin birdsfoot trefoil silage. Second year residual alfalfa manure plots had 35% greater corn yield and 50% greater corn nitrogen uptake than control plots that received no manure, followed by red clover, low-tannin birdsfoot trefoil, and high-tannin birdsfoot trefoil which had from 17% to 22% greater corn yield and 29% to 36% greater corn nitrogen uptake than control plots. These studies are expanding dairy nutrition research to develop rations that satisfy the nutritional demands of high producing dairy cows and produce manure that has desirable environmental properties, including the ability to recycle manure nutrients through crops.
Technical Abstract: More precise feeding of protein and mineral supplement reduces nutrient excretion in dairy manure and losses to the environment. No information is available on the impacts of feeding different forages to dairy cattle on manure N chemistry and subsequent N cycling in soils. Slurry (feces plus urine) from dairy cattle fed rations containing silages of alfalfa (ALF), red clover (RCL), low-tannin birdsfoot trefoil (LTBT), or high-tannin birdsfoot trefoil (HTBT) were applied (375 kg N ha-1) to field plots during spring only or spring plus fall. After spring application, slurry type did not significantly impact soil pH, and only periodically impacted concentrations of soil NH4-N and NO3-N. First year corn N uptake after spring application of ALF slurry was greater than corn N uptake after LBFT slurry application or in control plots. Second year residual ALF plots had 35% greater corn yield and 50% greater corn N uptake than control plots, followed by RCL, LTBT and HTBT plots, which had from 17% to 22% greater corn yield and 29% to 36% greater corn N uptake than control plots. Corn yield and N uptake were not significantly impacted by slurry types applied the previous fall. Average residual N recovery by corn in spring slurry-amended plots ranged from 20% (ALF) to 13% (RCL and LTBT). Total N recovery was likewise highest in ALF plots followed by RCL and LBFT. Low impacts of slurry types on soil chemical properties and corn was likely due to several interactive factors, including low rainfall, high indigenous soil N availability, and high response variability associated with indirect estimates of slurry N recovery.