FACTORS AFFECTING YIELDS AND UPTAKE OF PHOSPHORUS BY DIFFERENT CROPS

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Abstract
The residual effects of rock phosphate and superphosphate applied alone and in complete treatments to an upland soil of the Ozark Region for 32 years were assayed in the greenhouse with buckwheat, oats, and alfalfa by use of radioactive superphosphate. The field soil without phosphate pretreatment when treated with superphosphate in the greenhouse produced marked increases in yields and phosphate uptake of all crops. Soils pretreated with phosphate did not in every case bring crop response when treated with superphosphate. Buckwheat and oats took equal proportions of their phosphate from the fertilizer source. Alfalfa took proportionally only about half as much as the other two crops. Buckwheat recovered about 40% of the fertilizer phosphorus applied, oats about 12% and alfalfa about 4%. Fried and Dean A values varied markedly from crop to crop and from one soil pretreatment to another. Neither the Na HCO3 extractable nor the acid extractable phosphate correlated well with the A values obtained. The total uptake of phosphate from the fertilizer source was remarkably constant for any given crop, but it varied tenfold between crop extremes. A significant interaction was found between the nitrogen, potash, and lime of the pretreatment and the superphosphate applied in the greenhouse. It resulted in marked depression of the phosphate taken up by buckwheat and oats from the soil source. A possible explanation for this phenomenon was postulated on the basis of energy relationships.