CONTROL OF FALL NITRATE LEACHING FROM EARLY HARVESTED POTATOES ON PRINCE-EDWARD-ISLAND

The ability of a catch crop (winter wheat) and a lightly incorporated straw mulch to reduce NO3-N leaching following harvest of early potato es (variety Superior) on Prince Edward Island (PEI) was evaluated over two cycles of a potato-cereal rotation, from spring 1989 to spring 19 93. The extent of nitrate leaching from each treatment was indicated b y the mean annual (spring to spring) flow-weighted NO3-N concentration (NO3-N-f) of tile drainage water, Mean annual values for the winter w heat and barley crops in the rotation ranged from 2.9 to 7.7 mg/L. For the first potato crop, both fall treatments significantly reduced NO3 -N-f values, from 12.8 mg/L in the control to 10.7 mg/L for the straw incorporated and to 8.8 mg/L for the winter wheat crop. For the second potato crop, only the straw-incorporated treatment was significantly lower than the control, 27.5 compared to 18.0 mg/L. The relatively sho rt time available for plant biomass accumulation following fail planti ng in PEI appears to limit the ability of winter wheat to consistently reduce post-harvest NO3-N leaching. Soil profile NO3-N content measur ed by coring in late fall and early spring after potatoes were grown d id not show any significant differences among treatments.