by Sally Colby
It’s a given that manure application has the potential to cause conflict with neighbors, but it can also cause conflicts between the farm’s nutrient management plan and its conservation plan.
Doug Beegle, who conducted manure research at Penn State University, says nutrient management plans often recommend manure incorporation, but the conservation plan for the farm will often recommend no-till.
“The biggest reason people want to incorporate manure is to reduce ammonia volatilization and odor,” said Beegle. “It’s long-established that those are benefits of immediately incorporating manure.
Incorporating manure can also reduce soluble phosphorus loss, but in most cases, it will increase sediment-bound phosphorus loss due to increased erosion with tillage. Regular tillage also has an impact on soil quality.”
In no-till, the main benefit of manure is reduced erosion and improved soil quality. However, because manure is on the soil surface, there is increased ammonia volatilization and odor. “We can see increased soluble phosphorus losses because the manure is exposed on the surface,” said Beegle, “If there is runoff, it is interacting directly with the manure and can carry the soluble phosphorus out of the manure. But we do see significantly less sediment-bound phosphorus loss in no-till.”
Is there a means by which farmers can get the benefits of manure incorporation while retaining the benefits of no-till, and if so, what are the trade-offs? Beegle referenced low-disturbance manure incorporation research conducted in cooperation with USDA-ARS and Penn State University.
Shallow disk injection employs a large coulter that slits the soil, and a tube that runs next to the coulter deposits manure at the bottom of the slit. A mechanism behind the injectors closes the soil over the slit. “This creates slots that are 30 inches apart, with manure in the slot and soil covering the slot,” said Beegle. “There is very little soil disturbance and very little manure on the surface — similar to what you’d see in a no-till corn planter.” Beegle noted when researchers returned to manured fields to collect samples, it was sometimes difficult to find the injection bands in the soil. “That tells me that we’re doing a pretty good job of conserving that no-till environment.”
Another application method is using an aerator that applies bands of manure. “With this system, we have an aerator that rolls along, pokes holes in the ground which creates cavities. The manure is deposited in tubes right behind the aerator. The idea is that it enhances the infiltration of manure down into the soil.” Beegle noted that this method doesn’t actually inject the manure, and that a fair amount of manure remains on the soil surface; especially dairy manure with high solid content.
Manure application by either disk or aerator resulted in sufficient surface residue levels to meet the criteria for no-till. Aeration resulted in 24 percent less ammonia loss at the surface, while disk injection resulted in 79 percent less ammonia loss. “In our research, we’ve been trying to do the tillage within an hour or so after manure application,” said Beegle. “Ammonia loss from manure happens very quickly. It’s an important message for farmers who wait a week or more to incorporate manure. If they’re incorporating to reduce ammonia loss, that isn’t a legitimate reason to do the tillage — if they aren’t doing it the same day, they’re probably losing most of the ammonia.”
Dr. Quirine Ketterings, who works with nutrient management in agricultural systems at Cornell University, says that shallow incorporation of manure via aerator is of interest to New York farmers as a means of reducing ammonia emissions and increase nitrogen use efficiency, and is compatible with reduced tillage systems. “That’s attractive for many of our farmers,” she said. “There’s also potential for recued fuel and labor costs.”
In trials conducted across New York, results consistently showed that surface residue was preserved with aerator application. “The aerator leaves measurably more surface residue than incorporation with more aggressive tillage tools,” said Ketterings. “That can make a difference for meeting conservation tillage requirements (more than 30 percent residue preserved).”
Manure injection for ammonia conservation
by Sally Colby