Long-term influence of cropping systems, tillage methods, and N sources on nitrate leaching

The extent of nitrate leaching in cultivated soils of Alberta is unknown. We studied how long- and short-term agricultural practices influenced nitrate leaching in a cryoboreal subhumid soil-climate of north-central Alberta. The study used plots from three crop rotation-tillage studies at Breton on an Orthic Gray Luvisol, and from one at Ellerslie on an Orthic Black Chernozem. Soil samples were taken in the fall of 1993 from selected treatments as well as native forest sites in 0.3-m depth increments from 0 to 3.9 m and analyzed for NO 3 -N. No NO 3 − were found under native forest vegetation. NO 3 -N accumulated below 0.9-m depth of agricultural ecosystems cultivated for as long as 64 yr ranged from 0 to 67 kg N ha −1 . At Breton, fallow-wheat rotation plots receiving fertilizer N and manure contained eight times more NO 3 -N below 0.9 m depth than non-fertilized plots. NO 3 -N levels in an 8-yr legume-based rotation and in continuous-barley plots were similar but greater than in continuous-forage plots. Eighty-seven percent of NO 3 − found under continuous barley occurred below the root zone compared with only 35% in the 8-yr rotation. At Ellerslie, NO 3 -N mass was related to fertilizer N and mineralization of soil organic matter. Increased efforts should be directed towards better synchronizing N release from or addition to soils with plant uptake. Evidence of greater nitrate leaching under zero tillage than under conventional warrants further confirmation. Key words: Nitrogen loss, fallow, Hordeum vulgare L., Triticum aestivum L., manure, legumes, synthetic fertilizer