Yield and nutrient uptake of wheat on oil well sites: effects of topsoil depth and organic amendments

The effect of different depths of topsoil replacement and organic amendments on wheat yield on oil well sites was investigated, Three sites were utilized using a split-plot design with a depth of topsoil replacement at the main plot of 0, 50, 100, and 150 per cent. The subplots were treated with organic amendments of compost, fresh manure, alfalfa hay, wheat straw, and a control, as one-time applications in 1997. Results showed no effect on grain yield by topsoil depth. As far as the amendments were concerned, the straw-amended plots produced significantly lower yields than the other amendments. Nitrogen nutrition of the wheat was also unaffected by topsoil depths, but phosphorus uptake was lower, probably due to the sulfur being tied up by the subsoil. Alfalfa, compost and manure increased the nitrogen uptake of wheat while compost and manure increased the uptake of phosphorus. The wheat straw amendment reduced both the nitrogen and phosphorus uptake, with corresponding reduction in grain yield. It was concluded that while topsoil application is beneficial, increased application does not result in increased benefits. Indeed, minimum topsoil replacement depth may be advisable to prevent the negative consequences of subsoil on phosphorus nutrition. 4 refs., 5 tabs., 2 figs