Disposition of nitrogen in the soil-plant system for flax and spring wheat-containing rotations in the Brown soil zone

Recently, there has been a marked increase in the production of oilseed crops instead of hard red spring wheat (Triticum aestivum L.) in the semiarid Brown soil zone of Saskatchewan. In this study we compare the disposition of N and soil water in two 3-yr fallow-containing crop rotations, one with flax (Linum usitatissimum L.) and wheat, and the other with only wheat. These rotations were initiated at Swift Current, Saskatchewan, in 1967 on a silt loam soil, but this assessment applied to the 1985 to 1995 period when complete soil water, NO3-N, and plant N measurements were collected. Flax grown on fallow produced less plant biomass and N uptake was lower than for wheat grown on fallow; thus, it left more NO3-N and water in the soil (especially in the 60-120 cm depth) at harvest. This residual NO3-N and water following flax rarely resulted in higher grain yields or higher grain N concentrations in the succeeding stubble-wheat crop. We hypothesized that this excess NO3-N and water may leach and thereby increase contamination of groundwater.