What manure management practice, when performed correctly, will help farmers obtain the highest economical return from the manure? Which practice will help protect the environment the most? Is it filling out the required paperwork, annually sampling each manure source, taking soil tests at least once every four years for each field, recording all nutrient related activities for each field, calibrating manure applicators/spreaders? Alternatively, is it compiling soil grid maps, applying manure based on crop nutrient needs, using proper manure pit agitation, completing manure incorporation soon after application, utilizing a nitrogen stabilizer, or some other practice?
These are all important activities that either aid in utilizing the nutrients in manure or help comply with regulations. Some of these activities are required on many farms depending on its animal unit size and/or additional local ordinances. Paperwork and record keeping maintain a history of all these activities for compliance but also provide farm management tools. Sampling of soil and manure provide us information on how to manage these components. Calibrating equipment and proper agitation of pits help ensure even and correct distribution of the nutrients in manure. Calculating the appropriate amount of manure to apply based on crop needs and considering use of a nitrogen stabilizer when needed help to ensure the application of manure is adequate, not over applied, and is potentially available for the next crop.
All of the practices in the previous paragraph are important and necessary for properly managing manure. However, there is one practice that when not performed properly can cause substantial economic loss and can potentially lead to environmental issues; timely and adequate incorporation of all manure into the soil.
The economic loss from not incorporating manure is mainly from nitrogen losses due to volatilization illustrated by the accompanying chart. In the case of dairy manure, only 20% of the nitrogen is available for the first year's crop without timely manure incorporation, compared to 50 to 55% availability if properly and quickly incorporated into the soil. Is the difference between 20% and 55% nitrogen availability very significant? After all, it takes time to incorporate so soon after application.
Manure N Availability
|Year available||Broadcast incorporation timing||Injection|
|None||12 to 96 hrs.||<12 hrs.||Sweep||Knife|
|% of total Nitrogen available per year|
Hernandez, Schmitt. 2012. Manure Management in Minnesota, University of Minnesota Extension.
Let us study a couple of dairy situations. We will assume a typical dairy liquid manure analysis (each farm's manure source should be individually sampled annually) of 23% N, 12% P2O5, and 25% K2O applied at a rate of 12,000 gallons per acre. Utilizing commercial fertilizer prices for fall 2015 and using the University of Minnesota "What is Manure Worth Spreadsheet", the total value of this manure is about $200 per acre. If application costs are $100 per acre, the net manure value is around $100 per acre. If we do not incorporate that same manure within 4 days, it reduces the value of the manure about $50 per acre due to nitrogen losses. That is a $5,000 loss for each 100 acres of liquid manure applied.
Let us examine pen-pack manure with a typical analysis of 15% N, 7% P2O5, and 17% K2O applied at a rate of 12 tons per acre. When incorporated within 12 hours, the total nutrient value is about $170 per acre. If application cost of pen-pack manure is about $60 per acre, the net value is about $110 per acre. If incorporation of this pen-pack manure occurs after 4 days, it has a total value of about $130 per acre; when subtracting application costs of $60 per acre it nets a value of $70 per acre. That is a loss of $40 per acre or $4,000 for each 100 acres of pen-pack manure applied.
Chances are that most farmers already have the equipment necessary for incorporation of manure; it is usually a labor issue. Of course, it is not possible to incorporate manure on frozen or snow covered ground.
What is the environmental issue? Any phosphorus that reaches any surface water is an environmental problem. Locally we witness blue-green algae blooms from excess phosphorus. The Gulf of Mexico Hypoxic Zone at the Mississippi mouth is from excess phosphorus and nitrogen.
How do we lessen the environmental risk of phosphorus in our manure? When manure is on top of the soil, we expose the phosphorus enabling it to wash away during any rain or snowmelt event, even without soil erosion. When soil phosphorus levels are near normal levels (21 ppm Bray 1-P or 16 ppm Olson), most of the phosphorus attaches to soil particles within days after incorporation into the soil. The objective then is to incorporate manure into the soil as soon as possible after application.
The conclusion is that rapid and proper incorporation of manure into soil can potentially save us considerable money on nitrogen fertilizer expenses and will have a major effect on reducing phosphorus entering our surface water, which is an environmental issue.