The 27 plots per replicate were divided into three, nine-plot blocks separated by 10 m grass roadways to facilitate cultural and tillage operations. The study was replicated three times, each replicate separated from the other also by a 10 m grass roadway. The land had been crop to a wheat-fallow rotation since 1922 prior to initiation of this study. There are no trees, shelter belts, or other obstacles. A fence line and road are adjacent to the east side of the plots.
Winds are predominately from the west.
These plots were sampled for nutrients, soil moisture and plant growth at eight regular intervals during each growing season of the first 18 years of study. They were also sampled for straw and straw N and P at the same time. The dry matter yield and N and P content of the above ground plant material are also determined at each of these stages. All cropped plots are harvested and the yield and N and P content of the grain and straw are determined. Trash cover and aggregate stability analysis by dry sieving are measured on 6 of the rotations in the late fall of each year.