Field comparisons of colloidal phosphate and superphosphate as sources of phosphorus in potato fertilizers

Summary

Superphosphate, triple superphosphate, and mono-ammonium phosphate (Ammo-Phos) are the main sources used to supply phosphorus in potato fertilizers. As is generally recognized, growing potato plants require relatively large amounts of readily available plant nutrients. Although the amount of phosphorus absorbed is only about one-eighth to one-fourth of the amount of nitrogen and potash absorbed, the source of phosphorus must also be readily available to meet the needs of the potato plant for this essential plant nutrient. For a number of years a material designated Colloidal or Waste-pond Phosphate has been on the fertilizer market; at least it has been offered for sale to farmers who use fertilizer for crop production purposes. Potato farmers have been solicited to purchase the material on the strength of statements that its phosphorus is available and that, moreover, it has additional merit because of its content of certain so-called minor or secondary nutrient elements.

Field studies have been made in Maine, New Jersey, Pennsylvania, and Virginia to compare Colloidal Phosphate and superphosphate as sources of phosphorus in potato fertilizers, the results of which have shown:

• 1. In all field comparisons,—a total of 13 having been made,—potato plants receiving fertilizer mixture formulated with superphosphate produced greater yields than those receiving the fertilizer mixtures which had Colloidal Phosphate as the source of phosphorus. In Maine, the average increase for 8 tests was 68 bushels per acre in favor of superphosphate; in New Jersey, 1 test, 27 bushels per acre; in Pennsylvania, average of 2 tests, 24.5 bushels per acre; and in Virginia, average of 2 tests, 64 bushels per acre.

• 2. The more favorable influence of the superphosphate fertilizers on earlier emergence, vine development, tuber set, and number of marketable tubers produced was pronounced.

• 3. The results reported herein afford a pattern showing (1) that the use of Colloidal Phosphate as a source of phosphorus in potato fertilizers is not justifiable, and (2) that the maintenance of normal vine growth and maximum potato yields requires the use of a material high in available phosphorus as the source of phosphorus in potato fertilizers.