GROUNDWATER QUALITY UNDER CONVENTIONAL AND NO-TILLAGE - I - NITRATE, ELECTRICAL-CONDUCTIVITY, AND PH

The use of conservation tillage is increasing in North America, but in formation on its effect on water quality in cold climatic regions is l imited. To obtain such information, the effect of no-tillage (NT) and conventional tillage (CT) treatments on nitrate-nitrogen (NO3-N) conce ntration, specific electrical conductivity (EC), and pH in shallow gro undwater (1.2, 1.8, 3.0, and 4.6 m depths) was studied over four succe ssive 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 ev ery crop year and every season. However, the effect of tillage was not significant at P < 0.05. Nitrate concentration decreased significantl y 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 d epth, NO3-N concentrations were mostly low but increased with time. Ch anges 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 grou ndwater were not affected by tillage treatment. However, within each t illage treatment, values increased significantly with depth, Results f rom this study indicated a large spatial variability in NO3-N and EC v alues in groundwater, which could have masked small tillage effects, M ore intensive temporal and spatial sampling may be required to establi sh tillage treatment effects, if any.