The 4 Rs of Manure Management: Right Time

March 21, 2019

3.21.19 | The 4 Rs of Manure Management: Right Time from Central Valley Ag on Vimeo.

When is the right time to apply manure? When the crop is out of the field and the pens need to be cleaned out, right? There are a lot of compromises that must be made as we decide when we are going to apply manure.   Obviously, we need to keep our cattle pens, chicken barns, and hog pits in condition to maximize animal production and keep future storage available, so we manage our manure resource responsibly. A great time to make application is in the fall. The crop is out, the weather is nice (sometimes), and we get the freeze/thaw cycle to break up some of the compaction we create with all that heavy equipment in our fields. What if we can’t get it on in the fall? Springtime is generally a rush to plant, set up our weed control, and catch up on any fertility not already applied. Winter is tempting, but we need to be careful about putting manure on frozen soils especially when there is much slope to the field causing the opportunity for large amounts of nutrient-rich runoff.   

Besides the physical and environmental concerns about timing manure application, we need to think about the effect of application timing on the nutrient needs of the crop. Phosphorus, potassium, zinc, calcium, and most nutrients are best looked at from a long-term fertility perspective.  We are balancing the soil’s fertility with the needs of the crop and the likelihood of response given our soil test levels. In most cases, application timing is not as important as managing nutrient levels profitably. Nitrogen is the outlier here. Nitrogen just wants to get away from us. We want to get it in the crop, and it seems to want to disappear through leaching or denitrification. 

The best time to have nitrogen available for a crop is just before a crop really needs large amounts of it. In corn that is approximately V5-6. From V6 to R3 corn uses a tremendous amount of nitrogen. Timing some or even most of our nitrogen to match this uptake curve is the best way to get our applied nitrogen into the plant. We know that it does not make sense to apply most nitrogen fertilizer products in the fall. The one exception we sometimes allow is applying anhydrous ammonia in the fall in medium to fine-textured soils (silts & clays) when temps are under 50 degrees F and declining. This works for two reasons: 1) ammonium is relatively stable in the soil. 2) the bacteria that facilitate the conversion of ammonium to nitrate are killed by the causticness of anhydrous ammonia and recover slowly when temps are under 50 degrees. To help keep our N in ammonium form we will often add a bactericide such as N-Serve to our anhydrous ammonia to slow the conversion to nitrate.

When we apply manure, we need to understand the form of nitrogen we are applying. If the manure nitrogen is largely organic in form, then it will take mother nature, time, and warm temps to convert it to ammonia and eventually nitrate. If the manure N is largely in the ammonia form, then it can convert to nitrate rather quickly. If we are going to apply this manure N in the fall or early spring, we may want to try to protect it from converting to nitrate too early. Growers applying liquid manure products such as dairy or hog manure should consider using a nitrification inhibitor such as Instinct II from Corteva or More Than Manure from Verdesian. These products can help us get the nitrogen in the manure into our plants and keep it out of our groundwater or from being lost to our atmosphere.

By Tim Mundorf

Posted: 3/21/2019 4:15:38 PM by Kelli Emanuel | with 0 comments