Impact of potato-cereal rotations and slurry applications on nitrate leaching and nitrogen balance in sandy soils

Abstract

Groundwater quality is at risk when high levels of N fertilizers are used on sandy soils. A monitoring program was initiated in the summer of 1995, to quantify nitrate leaching in sandy soils used for potato production near Quebec city, Canada. Three drainable lysimeters were installed in each of five fields, for a total of 15 lysimeters. During a 5-yr monitoring period, crop N uptake, mineral and organic N fertilizers use, nitrate concentrations and fluxes from drainage water at 1-m soil depth were assessed under potato, cereal and hay crops. In one field, a clover and timothy sod that received low mineral N fertilizer inputs generated the lowest annual nitrate leaching losses ranging from 7 to 20 kg NO3-N ha-1. High nitrate leaching losses (116 ± 40 kg N ha-1) were measured under potato crops receiving high mineral N fertilizer inputs. Cereals, including barley and wheat receiving moderate mineral N fertilizer inputs and in some instance N from pig slurry, dairy cow manure or paper mill sludge, also generated high nitrate leaching losses (88 ± 45 kg N ha-1). Only sod and oat crops generated annual flux averaged nitrate concentrations lower than 10 mg NO3-N L-1, the accepted standard for drinking water, while higher concentrations, ranging from 13 to 52 mg NO3-N L-1, were recorded under barley, wheat and potato crops receiving moderate to high amounts of mineral N fertilizer. Nitrate flux concentrations were moderate during the cropping season (May-August), highest in fall (September-December) and lowest in the winter-early spring period (January-April). After 5 yr of survey, use of pig slurry and paper mill sludge in potato-cereal crop rotations (51 to 192 kg N ha-1 annually) with mineral N fertilizers (103 to 119 kg N ha-1 annually) resulted in nitrate leaching losses (87 to 132 kg N ha-1 annually), at least 20 kg N ha-1 more than N exported by crop at harvest. More than 60% of N applied as pig slurry seemed to be unaccounted for in the partial N balance that included crop N uptake and nitrate leaching, suggesting that important losses probably occurred through ammonia volatilization, denitrification, or N immobilization in soil organic matter and crop residues. Key words: Barley, lysimeter, nitrate leaching, nitrogen balance, pig slurry, potato