Enhancing soil infiltration reduces gaseous emissions and improves n uptake from applied dairy slurry
Rapid infiltration of liquid manure into the soil reduces emissions of ammonia (NH3) into the atmosphere. This study was undertaken to assess the effects of two low-cost methods of assisting infiltration of applied dairy slurry on emissions of NH3, nitrous oxide (N2O), and on crop N uptake. The two methods were removing of solids by settling-decantation to make the manure less viscous and mechanically aerating the soil. Ammonia emissions were measured with wind tunnels as percentage of applied total ammoniacal nitrogen (TAN) while emissions of N2O were measured with vented chambers. Mechanically aerating the soil before manure application significantly reduced emissions of NH3 relative to the nonaerated soil in spring (38.6 to 20.3% of applied TAN), summer (41.1 to 26.4% of applied TAN) and fall (27.7 to 13.6% of applied TAN) trials. Decantation of manure had no effect on NH3 emissions in spring, tended to increase emissions in summer and significantly decreased emissions in fall (30.3 to 11.1% of applied TAN). Combining the two abatement techniques reduced NH3 emission by 82% in fall, under cool weather conditions typical of manure spreading. The two abatement techniques generally did not significantly affect N2O emissions. Uptake of applied N by Italian ryegrass (Lolium multiflorum Lam.) was generally significantly greater with decanted than from whole manure but the effect of aeration was generally small and not significant. The study shows that low cost methods that assist manure infiltration into the soil may be used to greatly reduce ammonia loss without increasing N2O emissions, but efficacy of abatement methods is affected by weather conditions.