Date of Award
Master of Science
Plant, Soil and Environmental Sciences
Russell J. Lewis
Gary M. Lessman, Alexander Van Hook
The purpose of this investigation was to evaluate several techniques for measuring phosphorus (P) availability. The data obtained were used to compare the relative availability of applied and residual P. Plant P uptake and soil extraction methods were used in estimating the availability of applied and residual P. Five Tennessee soils and three extractant solutions used in three Southern states were utilized. The plants were started in nutrient solutions and then transferred to the soil. The plants grew in the soils for 20 days. Plant yields, 32P, total P and P uptake determinations were made. The extractable P data for the original soils showed similarities between some soils and differences between others. The Minvale high P soil was shown to have the highest extractable P. The 1 percent ammonium sulfate in 0.05 N Sulfuric Acid (Solution I) and the 0.03N Ammonia fluoride in 0.1N hydrochloric acid (Solution III) were very similar in their extracting abilities for the original soils. Solution III extracted more P than did Solutions I and II (0.7N NH4OAc in 0.54N HOAc adjusted to pH 4.8). The extractable P data of the cropped soils showed that Solution 111 again extracted more P than did either of the other two solutions. All the solutions were different from each other in their extracting abilities. Some cropped soils had similar extractable P values. There were, however, significant differences between the extractable soil P values of other soils. Significant correlations were obtained between plant uptake and extractable P using Solutions 1 and II. Both plant yield and extractable soil P after cropping were increased when P was added to the low P soils prior to growing the plants. No significant correlation was obtained between the available P ("A" value) and plant uptake. The "A" values did show the same trends as the extraction solutions. The major portion of the P in the plant came from residual sources. Phorphorus uptake from applied P ranged up to 42 percent of the total P in the plants.
Mulbah, Charles K., "Comparison of the availability of applied and residual phosphorus as measured by plant uptake and chemical analysis. " Master's Thesis, University of Tennessee, 1976.