Impacts of strategic tillage on soil erosion, nutrient loss in runoff and nitrous oxide emission

Abstract. Strategic (once-off) tillage (ST) of continuous long-term no-tillage (NT) soil may help to control weeds prior to establishing the following crop but may also increase the risk of erosion and nutrient loss in runoff and greenhouse gas emission compared with NT soil. The objective of this study was to measure these short-term runoff and gaseous emission impacts after ST of NT, controlled traffic farming soils. A rainfall simulator was used to generate runoff from four plots (2.75 m length x 0.75 m width) each of NT and ST on a Vertosol, Dermosol and Sodosol. Runoff was generated from heavy rainfall (70 mm h^-1) and samples analyzed for volume, sediment and nutrient contents. Short-term nitrous oxide (N₂O) emissions were measured from the Vertosol and Sodosol before and after rainfall using the passive chamber technique.

On the Dermosol and Sodosol there was more runoff from ST plots than from NT plots (P<0.05), however, volumes were similar between tillage treatments on the Vertosol (P>0.05). Erosion was highest after ST on the Sodosol (8.3 t ha^-1 suspended sediment) and there were no treatment differences on the other soils. Total nitrogen (N) loads in runoff followed a similar pattern. Dissolved phosphorus (P) concentrations and total P loads were higher (P<0.05) after ST than NT on both the Sodosol (3.1 and 0.9 kg ha^-1 of total P, respectively) and Dermosol (1.0 and 0.3 kg ha^-1 total P, respectively). Dissolved N and P fractions comprised less than 13% of total losses. ST did not increase N₂O emissions on either soil studied . (P>0.05) Over the measuring period, cumulative N₂O-N emissions from the Vertosol and Sodosol were approximately 1 and 0.6 g ha^-1, respectively. Strategic tillage for weed control increased the susceptibility of Sodosols and Dermosols to water, sediment and nutrient losses in runoff after heavy rainfall but had minimal impact on N₂O emissions.