Manage manure applications wisely this fall

Amber Moore, Extension Soil Specialist, University of Idaho

[A...] common method for dairy manure disposal [...] is field application. Applying manures to croplands has been shown to significantly improve yields, as manures are a rich source of nutrients. However, nutrient uptake is highly dependent on how the manure applications are being managed. Here are a few tips to help you get the greatest soil fertility value out of your field-applied dairy manure:

1. Spread manure in the fall instead of the spring.
Organic nitrogen compounds in the manure will have time to mineralize into plant-available forms (nitrate and ammonium) over the winter months, which will allow for greater nitrogen utilization by spring-planted crops. When manure is applied in the spring, organic nitrogen will likely not be mineralized until late in the season when the plants no longer need it.

2. Incorporate manure immediately after application.
Leaving manure on the surface for more than even a couple of hours will ensure significant losses of nitrogen as ammonia gas. Moving the manure into the soil surface will allow ammonium to attach to soil particles instead of literally evaporating into thin air.

3. Plant residue is a good thing.
Incorporating manure into fields that have plant residue on the surface will help to slow the nitrogen mineralization rates over the winter months. Otherwise, nitrates can leach downward into the soil profile, away from roots and toward sensitive groundwater resources. Growing winter cover crops, such as wheat or rye, is also an effective means for utilizing excess nitrates in the profile, as opposed to leaving the field fallow.

4. Have your manure tested.
You would never waste money on a fertilizer with an unknown N-P-K, so don’t do it for field-applied manure, either. Send a composite sample to be tested for dry matter content, total nitrogen, ammonium nitrogen, total phosphorus, total potassium, electrical conductivity, and if possible, total carbon to labs approved for manure analysis. Updated lists of certified manure-testing labs are available at www.mda.state.mn.us/licensing/pestfert/manurelabs.htm ANM

—Excerpts from University of Idaho Nutrient Digest, Fall 2008