Evaluation of ammonia emissions from manure incorporated with different soil aerator configurations

Abstract

The incorporation of swine manure with tillage effectively reduces ammonia (NH₃) emissions and conserves crop available nitrogen (N) but is not compatible with no-till and many other conservation tillage programs. Rolling-tine aerators potentially provide a means to enhance manure infiltration with limited disruption of the soil surface; however, the impact of the range of aerator configurations and manure placements has not been widely studied. We measured NH₃ emissions, conducted presidedress nitrate (NO₃) tests (PSNT), monitored corn (Zea mays L.) grain yield when swine manure was incorporated with combinations of two aerator toolbar offset angles (0° and 10°) and two manure placements (broadcast before aeration and banded behind aerator), and compared those measurements to unincorporated surface application and an unmanured control. Additional plots were established with five rates of mineral N fertilization to determine N response curve and estimate fertilizer N equivalent of the applied manure. Measurement of cumulative NH₃ emissions using a dynamic chamber method showed that offsetting the aerator toolbar by 10° reduced emissions by 65% to 75%, with both manure placements, compared to surface application. However, no consistent reductions in NH₃ emissions were observed when the toolbar was not offset. While reduction in NH₃ with the offset toolbar could conserve substantial amounts of plant available N, the soil disturbance caused by the offset tines would not be compatible with most conservation tillage programs. Presidedress NO₃ test values increased when NH₃ emissions were reduced. In 2009, both the angled and straight aerator treatments with manure banded behind the aerator resulted in significantly higher corn grain yield than all other treatments despite reductions in NH₃ emissions only when the toolbar was angled. Correlation of yield from manure application treatments with the N response curve for multiple mineral N application rates showed a greater than expected response to manure application. Yield responses are an indication that aeration has benefits in addition to N conservation. We do not recommend the rolling-tine aerator if reducing NH₃ emissions in conservation tillage is the primary goal, but future study into other yield-increasing benefits of aeration is needed.