A Comparison of Ammonium Metaphosphate and Ammonium Orthophosphate with Superphosphate on the Yield and Chemical Composition of Crops Grown Under Field Conditions
1959
Godfrey, Curtis L. | Fisher, Flake L. | Norris, M. J.
Sweet Sudan and Iron-Clay cowpeas were grown under irrigation in the field on a Lufkin fine sandy loam, an acid Planosol, and on a San Saba clay, a highly calcareous Grumusol (Rendzina). The plots were fertilized with 50-30-60 per acre, with the check receiving 50-0-60. The treatments consisted of ammonium sulfate, ammonium orthophosphate, ammonium metaphosphate, 20% superphosphate, muriate of potash, and calcium sulfate, applied in such a way as to give a valid comparison between the ammonium phosphates and superphosphate. The forage from one-half the area of each plot was harvested 4 weeks after planting and the remainder at the end of 8 weeks. Forage yields and chemical composition were determined. Crops at both locations responded to all P treatments, with the Sudan yields being increased about 90% over the check in contrast to only about a 10 to 15% increase by the cowpeas. The greatest yield response was by Sudan on the San Saba clay; the least response was by the cowpeas, also on the San Saba clay. All sources of P were about equal in their separate effect on crop yields at each location. The P content of the separate crops was increased about the same by each source of P, but the P content was highest in the crops grown on the acid Lufkin fine sandy loam. The P content of the cowpeas grown on the San Saba clay was not appreciably affected by P additions. The N, S and Ca levels in the forage were not affected by the P treatments, but were affected by location and species, and were greatly affected by the stage of maturity at harvest, the less mature forage being higher in these nutrients.
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