Impacts of low-disturbance dairy manure incorporation on ammonia and greenhouse gas fluxes in a corn silage-winter rye cover crop system

Abstract

Manure and fertilizer applications contribute to greenhouse gas (GHG) and ammonia (NH₃ ) emissions. Losses of NH₃ and nitrous oxide (N₂ O) are an economic loss of nitrogen (N) to farms, and methane (CH₄ ), N₂ O, and carbon dioxide (CO₂ ) are important GHGs. Few studies have examined the effects of low-disturbance manure incorporation (LDMI) on both NH₃ and GHG fluxes. Here, NH₃ , N₂ O, CH₄ , and CO₂ fluxes in corn (Zea mays L.)-winter rye (Secale cereale L.) field plots were measured under fall LDMI (aerator/band, coulter injection, strip-till, sweep inject, surface/broadcast application, broadcast-disk) and spring-applied urea (134 kg N ha^-1 ) treatments from 2013 to 2015 in central Wisconsin. Whereas broadcast lost 35.5% of applied ammonium-N (NH₄ -N) as NH₃ -N, strip-till inject and coulter inject lost 0.11 and 4.5% of applied NH₄ -N as NH₃ , respectively. Mean N₂ O loss ranged from 2.7 to 3.6% of applied total N for LDMI, compared with 4.2% for urea and 2.6% for broadcast. Overall, greater CO₂ fluxes for manure treatments contributed to larger cumulative GHG fluxes compared with fertilizer N. There were few significant treatment effects for CH₄ (P > .10); however, fluxes were significantly correlated with changes in soil moisture and temperature. Results indicate that LDMI treatments significantly decreased NH₃ loss but led to modest increases in N₂ O and CO₂ fluxes compared with broadcast and broadcast-disk manure incorporation. Tradeoffs between N conservation versus increased GHG fluxes for LDMI and other methods should be incorporated into nutrient management tools as part of assessing agri-environmental farm impacts.