Remembering the 4Rs when Applying Manure
By Katie Drewitz, University of Minnesota Extension
PRESTON and CALEDONIA, Minn. (9/19/2023) — As we head into Fall it is time to think about Fall field work. For many Fall is the time for manure application to fields. Manure is a valuable fertilizer. In order to get the most value for next year’s crop, and avoid runoff and leaching we need to remember the 4Rs. The 4Rs are Right Source, Right Rate, Right Time and Right Place.
There are many sources of fertilizer and you need to make sure that you are taking credits for the ones that you are using including manure. In relation to fertilizers used in conjunction with manure we need to especially consider nitrogen and phosphorus. Will you use a commercial starter fertilizer that contains nitrogen or phosphorus at planting? Was last year’s crop a legume? Was manure applied last year on this field? Does your irrigation water contain nitrogen? If you answered “yes” to any of those, make sure to take credit!
When it comes to fertilizer, more is not better. You need to apply the appropriate rate that allows the correct amount of nutrients for your crop without over applying. Over application is bad for your bottom line and the environment. Check out the current guidelines for manure application rates on the University of Minnesota Extension website or contact your local Extension educator to help you determine the nitrogen and phosphorous rates for your crop. Be sure to use all of the information that you have available to ensure you’re applying the right rate. This includes your soil test results and manure nutrient analysis. Finally, be sure to calibrate your spreader to apply your determined rate.
When the weather is changing and storage units are filling, right timing can be one of the more challenging 4Rs. To avoid nitrification and other nutrient loss we recommend applying manure when soils are 50 degrees F or cooler. This is especially important for liquid or slurry manures that have a higher proportion of inorganic nitrogen that is more easily nitrified. Note that nitrification is not halted at cool temperature, just slowed. Even around freezing, the process continues very slowly.
Finally you want to ensure that you are applying in the right place. Record keeping is an important aspect of farm management and your nutrient plan is no exception. While we often think of manure as “free fertilizer” you already paid for these nutrients when you purchased the feed for the livestock. Again, over application does not benefit your crop, field, bottom line or the environment. You will want to prioritize fields that can benefit from all of the nutrients in manure, not just the nitrogen. Having a manure management plan in place for your entire operation can be beneficial to help you get the nutrients to the fields where they are needed. Then you can plan for additional commercial fertilizers as needed to balance everything out.
The information in this article and additional details can be found on the University of Minnesota Extension website by searching “4Rs” and clicking on the article. You can also reach out to your Local Extension Educator. Residents in Fillmore and Houston counties can call 507-765-3896 or 507-725-5807.