Evaluation of Calcium Ammonium and Calcium Potassium Pyrophosphates as Fertilizers 1

Six calcium ammonium and calcium potassium pyrophosphates were tested in the greenhouse as sources of P and N or K for two successive crops of corn forage on limed and unlimed Hartsells fine sandy loam. The fertilizers were applied as powders and as pellet-granules; the residues of the granules were examined petrographically after harvest of the second crop. The granules were much less effective than the powders as sources of P and N for the first crop, but only slightly less effective as sources of K. The powders were nearly as effective as superphosphate as sources of P and one of the ammonium compounds was nearly as effective as (NH₄)₂SO₄ as a source of N, but none of the K compounds was as effective as K₂SO₄ as a source of K. The chemical alterations of the pyrophosphates in the soil were much like those of the same compounds in water, and all the observed alteration products were pyrophosphates. Some of the pyrophosphates show promise as long-term, slow-release sources of P and N or K.