Landscape position effects on the recovery of 15N-labelled urea applied to wheat on two soils in Saskatchewan, Canada

Information on the relative efficiency of fertilizer N at different landscape positions is needed to develop variable rate N fertilizer recommendations and to optimize crop yield with precision agriculture. The objective of this study was to determine the effect of landscape position on yield, N uptake, recovery of applied fertilizer N in plant and soil, and % of plant N derived from fertilizer (% Ndff) in heads, straw and roots of wheat. Field experiments (2 years on a Dark Brown Chernozemic soil at Watrous and 3 years on a Black Chernozemic soil at Prince Albert) were conducted in Saskatchewan, Canada. The N-15-labelled fertilizer technique was used to compare the results from microplots (45 x 45 cm) located at lower and upper slope positions. At Watrous, yield, N uptake, and recovery of applied N in heads, straw and roots of wheat were greater in 1 year and tended to be greater in the second year at lower slope positions compared to upper slope positions. The opposite was true for % Ndff, which was less in heads, straw and roots in 1 year and tended to be less in the second year at lower slope positions compared to upper slope positions. The recovery of applied N in soil or plant plus soil was less at lower slope positions than at upper slope positions in 1 year. At Prince Albert, the influence of slope position was not significant in most cases, but there was a consistent trend of slightly greater yield and N uptake, and somewhat smaller recovery of applied N in heads, % Ndff in heads, straw and roots, and recovery of fertilizer N in soil or plant plus soil at lower slope positions compared to upper slope positions. The differences between the two slope positions were relatively large and significant in many cases at Watrous, due to relatively drier soil conditions at the upper slope position than at the lower slope position in 1998. However, the differences were usually small and not significant at Prince Albert, due to relatively adequate soil moisture conditions on both slope positions.