Gaseous and leaching nitrogen losses from no-tillage and conventional tillage systems following surface application of cattle manure

Abstract

Previous studies have demonstrated inconsistent results on the impact of tillage systems on nitrogen (N) losses from field-applied manure. This study assessed the impact of no-tillage (NT) and conventional tillage (CT) systems on gaseous N losses, N 2O:N 2O + N 2 ratios and NO 3 −-N leaching following surface application of cattle manure. The study was undertaken during the 2003/2004 and 2004/2005 seasons at two field sites in Nova Scotia namely, Streets Ridge (SR) in Cumberland County and the Bio-environmental Engineering Centre (BEEC) in Truro. Results showed that the NT system had higher ( p < 0.05) NH 3 losses than CT. Over the two seasons, manure incorporation in CT reduced NH 3 losses on average by 86% at SR and 78% at BEEC relative to NT. At both sites and during both seasons, denitrification rates and N 2O fluxes in NT were generally higher than in CT plots, presumably due to higher soil water and organic matter content in NT. Over the two seasons, mean denitrification rates at SR were 239 and 119 g N ha −1 d −1, while N 2O fluxes were 120 and 64 g N ha −1 d −1 under NT and CT, respectively. At BEEC mean denitrification rates were 114 and 71 g N ha −1 d −1, while N 2O fluxes were 52 and 27 g N ha −1 d −1 under NT and CT, respectively. Conversely, N 2O:N 2O + N 2 ratios were lower in NT than CT suggesting more complete reduction of N 2O to N 2 under NT. When averaged across all soil depths, NO 3 −-N was higher ( p < 0.05) in CT than NT. Nitrate-N decreased with depth at both sites regardless of tillage. In most cases, NO 3 −-N was higher under CT than NT at all soil depths. Similarly, flow-weighted average NO 3 −-N concentrations in drainage water were generally higher under CT. This may be partly attributed to higher denitrification rates under NT. Therefore, NT may be a viable strategy to remove NO 3 −-N from the soil, and thus, reduce NO 3 −-N contamination of groundwater. However, it should be noted that while the use of NT reduces NO 3 −-N leaching it may come with unintended environmental tradeoffs, including increased NH 3 and N 2O emissions.