Long-Term Erosion-Productivity Relationships: The Lethbridge Soil Scalping Studies.
Soil erosion by wind or water removes valuable topsoil and decreases soil productivity. What is the value of this topsoil in terms of maintaining crop yield? When restoring eroded soils, how long do the effects of one-time applications of soil amendments last and is the magnitude or longevity of these effects influenced by the level of erosion? This study was conducted to answer these questions and ascertain the effects of simulated erosion on soil productivity and methods for its amendment. Incremental depths (0, 5, 10, 15, and 20 cm) of surface soil, or cuts, were mechanically removed to simulate erosion at two sites (one dryland, one irrigated) in southern Alberta in 1990. This approach is often referred to as ‘soil scalping’. Three amendment treatments (nitrogen + phosphorus fertilizer, 5 cm of topsoil, or 75 Mg ha-1 of feedlot manure) and a check were superimposed on each cut. The sites have been cropped annually since 1990 with no further amendments. Average grain yield reductions during the first 16 yr were 10.0% for 5 cm, 19.5% for 10 cm, 29.0% for 15 cm, and 38.5% for 20 cm of topsoil removal. There was evidence that the restoration of productivity levelled off at a value less than the non-eroded treatment rather than gradually converging on it, within the timeline of the study. Also a one-time application of livestock manure at the outset of the experiment was able to compensate for topsoil loss, especially in the early years of the study. The study reinforces the need to prevent soil erosion and indicates that application of livestock manure is an option for restoring soil productivity in the short term.
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