Yield and Nutrient Uptake of Wheat on Oil Well Sites: Effects of Topsoil Depth and Organic Amendments

This study was conducted to determine the effect of different depths of topsoil replacement and organic amendments on the productivity of well sites. The experiment was initiated in 1997 on three oil well sites at Strathmore, Hesketh and Rosedale using a split-plot design with the depth of topsoil replacement as the main plot (0, 50%, 100% and 150% of recommended replacement depth). The subplot treatment was organic amendments: compost, fresh manure, alfalfa hay, wheat straw and a control as one-time applications in 1997. There was no effect of topsoil depth on grain yield, but yields from straw-amended plots were significantly lower than other amendments. Also topsoil depth did not influence nitrogen nutrition of wheat but phosphorus uptake was lower at the lower topsoil depths due to the tie-up of phosphorus by the subsoil. Alfalfa, compost and manure increased the nitrogen uptake of wheat, while compost and manure increased
phosphorus uptake. The wheat straw amendment reduced both nitrogen and phosphorus uptake possibly via immobilization leading to a reduced yield. The results indicate that the application of topsoil is beneficial for crop growth but that diminishing returns set in at high topsoil replacement depths. A minimum topsoil replacement depth may be needed to prevent the negative impact of subsoil on P nutrition.