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Successful agriculture is dependent upon the maintenance of soil fertility. The problem of maintaining the fertility of our soils is not new. Since the early settlers first tilled the soil, more fertility or plant food has been taken out of the soil than has been returned through soil building practices. The high productivity of virgin soils has been attributed to their higher content of plant food and organic matter. Continuous cropping has depleted our soils of a considerable portion of their original plant food. This is especially true for the plant food elements nitrogen and phosphorus. Maintenance of the productive capacity of the soil requires the restoration of plant food through soil improvement practices which include returning manure, crop residues, plowing under legume crops, and the application of fertilizer. Of the ten primary elements essential for the growth of crops, only three may be deficient in soils, nitrogen, phosphorus and potash. These elements or plant food materials occur naturally in the soil in varying amounts, depending upon the type of soil and past soil management practices. When the fertility of the soil is not high enough for maximum crop production, plant food may be added by the application of fertilizers. In order to determine the kind and quantity of plant food to apply to the soil it is necessary to conduct field trials with fertilizers. Therefore, experiments are being conducted on different soil types and with different crops to determine the fertilizer need of South Dakota soils.

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Agricultural Experiment Station, South Dakota State College