The development of a whole-farm nutrient balance is the concept that involves balancing the amount of nutrient inputs across an entire operation (fertilizer, animals and feed) and comparing it to the nutrients leaving the operation (milk, meat, crops and manure). This concept applies to all operations, both large and small. In order to comply with regulatory nutrient management plan requirements, larger operations must demonstrate that manure will be handled and applied on an agronomic basis and the operation is designed for a whole-farm balance. For smaller operations that do not have as strict regulatory requirements, efficiently minimizing excess inputs while utilizing manure nutrients is essential for sustainability.

Changing ration ingredients, which often influence the overall level of dietary nutrient level, directly impacts the amount of land required to apply the manure produced. While most rations are balanced to specific dietary nitrogen and phosphorus levels, when certain alternative ingredients, such as corn gluten or distillers grains with solubles (DDGS) are used, they can increase the levels above minimum baseline formulation specifications. However, these types of ingredients, while raising diet nutrient levels in some cases, do not necessarily negatively impact a farm nutrient balance. If an operation has more land to apply manure, or has waste treatment systems that handle manure more effectively, their impact can be minimal from a manure management standpoint. However, if an operation has a limited land base or available acres to spread or transfer manure to other producers, the effect is much more pronounced.

Historically, large dietary margins of safety, especially for phosphorus, have been used by nutritionists not to limit performance of both market and breeding animals. However, these margins have been reduced substantially as the price of supplemental phosphorus and other feed ingredients have increased over the past couple years. Since feeding nutrients above the animal’s requirement simply increases excretion, not absorption and utilization, the manure level of these nutrients simply increase. Historically, dietary phosphorus in the form of mono- or di-calcium phosphate has been used to increased ration levels. However, various other feed ingredients also contain higher levels of phosphorus, such as DDGS. While DDGS has recently received the most attention for increasing nutrient levels of manure, which is mainly due to the increase in its supply and use in rations over the past few years as the ethanol industry has grown, this is not a new concept when using various ingredients in combination that increase diet and subsequently manure nutrient levels.

In a recent publication, Impact of Feeding Distillers Grains on Nutrient Management Planning on Dairy Farms, different ration combinations were outlined in case examples of using different dietary levels of DDGS on a nutrient management plan, the costs associated with its implementation and the changes necessary to comply with environmental regulations. While this case example is specific for feeding DDGS, the same principles can be applied to any ingredient that increases the amount of phosphorus and/or nitrogen in the diet.

To estimate the change in nitrogen and phosphorus excretion and subsequent change in nutrient management plan, four rations were evaluated for two case study farms, a 200- and 2,000-head lactating dairy herd. The low phosphorus baseline diet (0 percent DDGS) was formulated for a crude protein and phosphorus concentration of 18.5 percent and 0.33 percent DM, respectively. This diet was then modified to include 15 percent (18.5 percent CP; 0.39 percent phosphorus DM) or 30 percent (20.4 percent CP; 0.45 percent phosphorus DM) DDGS. The 30 percent DDGS inclusion rate exceeds most recommended levels for dairy cattle (generally recommended at 10-15 percent DM) but was considered within the realm of possibility for the near future. Finally, a high phosphorus diet (18.5 percent CP; 0.50 percent phosphorus DM) more representative of historical feeding practice was also included for comparison. For agronomics, the authors used a corn silage and alfalfa scenario for manure application. To view the complete assumptions, refer to the factsheet “Impact of Feeding Distillers Grains on Nutrient Management Planning on Dairy Farms” which can be accessed at www.extension.org/pages/Distillers_Grains_Fact_Sheets.

When applying manure to corn silage and alfalfa crops, the authors reported that the inclusion of 15 percent DDGS in a dairy cow diet would have minimal effects on the land required for manure management compared to the low baseline diet. On a phosphorus land application basis, approximately 1.4 acres per cow were required for both the low baseline and 15 percent DDGS diet. However, the acreage required increased to 1.7 and 2.0 acres for the 30 percent DDGS and historical high phosphorus diet, respectively. In contrast, using a nitrogen land application basis, the low baseline, historical high phosphorus and 15 percent DDGS diets all resulted in approximately 1.4 acres required per cow. However, for cows fed 30 percent DDGS, the acreage slightly increased to approximately 1.6 acres per cow required for manure application.

This data clearly indicates that changing ingredients that contain higher levels of nitrogen (crude protein) and/or phosphorus alters the land requirements for manure application. However, and just as importantly, feeding to the animals’ requirement and minimizing safety margins is critical to reduce needed acres for manure application while also reducing feed cost. Implementing a thorough feed ingredient testing program will help establish more confidence in nutrient values used in diet formulations; thus excesses can be reduced compared to using unknown ingredient nutrient levels where margins of safety are increased to prevent potential deficiencies or loss of production. ANM

Joel DeRouchey
Professor for Kansas State University
jderouch@ksu.edu