Vertical Tillage to Reduce Ammonia Volatilization and Conserve Residue after Dairy Manure Application.

The loss of nitrogen (N) in surface-applied dairy manure through volatilization as ammonia (NH₃) is a primary concern both economically and environmentally. Manure incorporation by conventional tillage has been shown to greatly reduce NH₃ losses, but the associated reduction in surface residue may lead to increased erosion. Vertical tillage, as a form of conservation tillage, has become popular in recent years, and a number of implements with varied functionality are being marketed for this purpose; its effectiveness for incorporating manure is not well researched however. We compared incorporation of dairy manure by vertical tillage (Case IH 330 or Great Plains turbo max 1800) and chisel plow, compared to surface broadcast, to assess their effect on NH₃ losses (measured with Ogawa passive samplers) and residue conservation. Vertical tillage by both implements reduced NH₃ concentrations substantially compared to surface broadcast levels (by 44-87%). Residue coverage after vertical tillage was 39% of that of control plots on average while chisel plowed plots averaged only 22%. The more aggressive Case IH implement reduced both NH₃ concentrations and residue cover to levels similar to those from chisel plowing, while both NH₃ concentration and residue cover from the Great Plains implement were statistically higher than chisel plowing in one of two trials. Our results showed that vertical tillage to incorporate manure can be effective at reducing NH₃losses and conserving residue, but there may be differences depending on specific tillage implements.