EFFICACY OF INORGANIC FERTILIZERS IN RESTORING WHEAT YIELDS ON ARTIFICIALLY ERODED SOILS

Chemical fertilizers are often used to amend eroded agricultural land. However, the relationships between level of erosion, nitrogen (N) rate and phosphorus (P) rate in restoring soil productivity are unclear. In 1990, experiments were initiated to examine the effect of three levels of erosion (0, 10 and 20 cm of topsoil removal to simulate non-eroded, moderately eroded and severely eroded soils), four rates of N and three rates of P on the performance of spring wheat (Triticum aestivum L.) for four southern Alberta soils. Residual erosion and fertilizer effects were assessed in a second cropped year. Erosion significantly decreased grain and straw yield at all four sites in the initial year. Removing 10 and 20 cm of topsoil reduced non-fertilized production by 43-66% and 60-85%, respectively, as compared with the undisturbed non-fertilized plots. Except for one site in the initial year, additions of N and P only partly remedied these losses. Responses to N and P were highest at moderate levels of erosion at three sites. There was a greater yield overlap between moderately and severely eroded treatments than between non-eroded and moderately eroded treatments, implying that the restoration of productivity is more difficult once the shallowest layer of topsoil has been removed.