Groundwater quality under conventional and no-tillage. I. Nitrate, electrical conductivity, and pH

The use of conservation tillage is increasing in North America, but information on its effect on water quality in cold climatic regions is limited. To obtain such information, the effect of no-tillage (NT) and conventional tillage (CT) treatments on nitrate-nitrogen (NO3-N) concentration, specific electrical conductivity (EC), and pH in shallow groundwater (1.2, 1.8, 3.0, and 4.6 m depths) was studied over four successive crop years in corn fields (loam soil) of approximately 3 ha each, located in eastern Ontario. Water table elevation was also monitored during three crop years. Average NO3-N concentration at the 1.2, 1.8, and 4.6 m depths was consistently higher under CT than under NT in every crop year and every season. However, the effect of tillage was not significant at P 0.05. Nitrate concentration decreased significantly with depth. It was about two to three times the drinking water limit of 10 mg/L as NO3-N at the 1.2, 1.8, and 3.0 m depths. At the 4.6 m depth, NO3-N concentrations were mostly low but increased with time. Changes in water table elevation appeared to affect NO3-N concentrations at the 1.2 m depth under NT only. At a given depth, EC and pH of groundwater were not affected by tillage treatment. However, within each tillage treatment, values increased significantly with depth. Results from this study indicated a large spatial variability in NO3-N and EC values in groundwater, which could have masked small tillage effects. More intensive temporal and spatial sampling may be required to establish tillage treatment effects, if any