The effect of long-time fertility treatments on the nitrogen and carbon content of a prairie soil

Nitrogen and carbon studies of the surface 6 2/3 inches of a prairie soil have been conducted since 1911 on the soil fertility plots at the Kansas Agricultural Experiment Station, Manhattan, Kans. This paper contains results of 1946 analyses of samplings on these plots and compares long-time trends in nitrogen and carbon with fertilizer applications, cropping systems, yields of dry matter, and carbon:nitrogen ratios. This study has lead to the following conclusions: 1. There has been a continual over-all loss of nitrogen and carbon over the entire period of the experiment regardless of cropping system or fertilizer treatment. Plots with the highest nitrogen content at the beginning of the experiment have suffered the greatest losses. 2. Fertilizer treatment had no influence on the nitrogen trends in the soil or on carbon:nitrogen ratios. 3. The loss of nitrogen was essentially the same on the 16-year and 3-year rotations, while with continuous wheat the nitrogen content of the soil has nearly reached an equilibrium. 4. The loss of carbon has been greater on the 3-year rotation and continuous wheat plots than with the 16-year rotation. 5. Yields of dry matter were highest for the rotation containing alfalfa and for complete fertilizer treatments, but these had relatively little influence on the carbon and nitrogen levels of the soil. 6. The average carbon:nitrogen ratios for continuous wheat and for the 3-year rotation remained essentially the same over the period of the experiment, but the ratio for the 16-year rotation has widened during the entire period. 7. As indicated by the results of this experiment, the cropping systems and fertilizer treatments studied on this soil have had only slight influence on the trend of nitrogen and carbon but may have some influence on the speed with which an equilibrium is reached and also the ultimate level.