Yield Response in Experiments With Phosphorus Fertilizers in Relation to: II. Variability and Differences Among Sources on Soils of Northern and Western States

Abstract

AbstractYield results from 124 experiments in Colorado, Iowa, New York, and Washington comparing phosphorus rates and sources, each including a response curve with CSP, were summarized in regard to the nature of the response and experimental error. In less than 10% of the tests with corn, small grain, and vegetables showing response to P was it possible to measure differences among sources from one‐half to twice as effective as CSP. Although experimental error was important, low response to applied P was the chief factor limiting the measurement of differences among sources. Coefficient of variation (CV) decreased with increase in mean yield of corn experiments in Iowa. Numerical increases in yields resulting from applied P were about the same at all yield levels in these experiments.