Changes in Organic Matter and Certain other Soil Constituents in Forty Years of Cropping Under Irrigation1

In 1911 a 10-year rotation, including 6 years of alfalfa, was laid down under irrigation at Lethbridge, Alberta Soil samples were taken at the beginning of the experiment and again in 1922, 1940 and 1951. During the 40-year period the soil has become more alkaline but no significant changes occurred in respect to the phosphorus and potassium status of the soil There have been significant increases in total nitrogen and organic matter content In terms of the 1911 values, the nitrogen increased by 7 0 per cent and the organic matter by 10 5 per cent in the surface 6 inches At, the 6- to 12-inch depth, the increases were 42 5 and 45 2 per cent, respectively