The phosphorus concentration of the exuded sap of corn as a measure of the available phosphorus in the soil
1933
Pohlman, G.G. | Pierre, W.H.
The determination of the PO4 content of the exuded sap of corn plants is suggested as a method for measuring phosphorus deficiency in the soil. This sap appears to offer all the advantages of the expressed juice without such disadvantages as the possibility of change in composition due to expression. In addition, it is easier to collect and analyze than is the expressed plant juice. The amount of inorganic PO4 found in corn sap varied from 62 to 602 p.p.m. Usually the amount increased with the age of the plant. The results obtained under greenhouse conditions show a good correlation with the response of corn to phosphate fertilization and also with the water-soluble PO4 and the available PO4 as determined by the Truog method. The data seem to justify additional tests with the method in order to ascertain limiting concentrations of PO4 for normal growth. Certain factors, such as light, temperature, moisture condition of the soil, supply of other nutrients, age and metabolic condition of the plant, and height of cutting, may affect the results and these should be considered in further studies of the method. Although no data are presented in this paper to show the concentrations of other nutrients in the exuded sap it would appear that the method might be used to advantage in a study of the availability of various elements, particularly nitrogen and potassium.
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