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The continuous production of farm crops without the return of a substantial quantity of the plant food removed by the crops will result in a shortage of plant food in the soil. Investigations conducted by the South Dakota Agricultural Experiment Station reveal that our cultivated soils have lost in the past 50 years approximately 40% of their original content of organic matter. Associated with this loss is the loss of 29% of the original nitrogen content of the soil which is a constituent of organic matter. Continuous cropping has also depleted our soils of a considerable portion of other plant food, especially phosphorous. The rate of plant food removal from the soil is proportional to the crop yield. For example, a 50 bushel crop of corn requires 80 pounds of nitrogen, 20 pounds of phosphorous and 55 pounds of potassium. This is equivalent to the plant food in approximately 600 pounds of complete fertilizer. Improved varieties of cereals and hybrid corn which are capable of producing higher crop yields are also increasing the rate at which plant food is removed from the soil. In order for the improved crops to produce maximum yields an adequate amount of plant food must be available to them in the soil. It now appears that it is necessary to give more attention to the soil fertility factor in crop production in South Dakota.

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Agricultural Experiment Station, South Dakota State College