Typically, liquid manure in NW Iowa is land- applied in the fall, as it gives us the greatest timeframe to get manure pumped. However, fall conditions are not always fit to apply manure, and fall manure application can lead to higher soil erosion losses and nutrient losses through leaching, volatilization, and runoff.
Early fall manure application, applied when the soil temperature is above 50 degrees, can have detrimental effects on yields and can be a costly decision. In Iowa State field trials, late fall manure application on corn/bean rotation
averaged 40 bushel/acre greater yield than early fall manure application when soil temperatures were above 50 degrees. In the same study, spring manure had an 18 bushel/acre yield advantage over late fall applied manure, and, similarly, a 38 bushel/acre yield advantage in continuous corn was seen when manure was spring-applied versus late fall (3 yr studies from 2016-2018).
Obviously, not all of our manure can be applied in the spring, but there is certainly strong evidence that spring manure application can be advantageous versus early fall manure application when soil temperatures are above 50 degrees and may be worth looking at trying.
Other advantages of spring-applied manure are reduced soil erosion, reduced nutrient loss, and less nitrate loss from tile lines.
Kris Kohl, ISU Extension Ag Engineering Specialist, offers some tips on applying spring manure and reducing compaction:
- Lower tire pressure to the lower end of the tire manufacturer recommended range.
- Wait for soil conditions to support loads.
- Till end rows where traffic has caused the most compaction.
Spring manure does take a little more planning and patience. Doing things like driving on the same track on the end rows and then deep tilling this afterwards are very important. Letting the field dry a little after application and then field cultivating (not disking) prior to planting to avoid clodding will make for a better seed bed and hopefully get the crop off to a better start.
Sometimes a little trial and error are necessary, but farmers who consistently spring apply manure attest to the benefits of higher yields.