Research Progress Report 300 March, 1967
Phosphorus and Potassium Fertilization of Continuous Soybeans on Blount Silt Loam, 1962-65

R. K. Stivers, M. W. Alderfer and J. R. Hodges
Department of Agronomy and AES Farms

Procedure
The purpose of this research was to determine the most economical rates of phosphorus (P) and potassium (K) fertilization of continuous soybeans on this Blount silt loam.

A field recently purchased by the Herbert Davis Forestry Farm near Farmland, was selected for these experiments. The fertilizer history of this field was unknown. The 1961 crop was wheat with a sweet clover seeding. There was only a fair stand of sweet clover before plowing in late spring, 1962.

Composite soil samples of 15 to 20 cores per plot were taken to a depth of 7 inches prior to initiating the experiment and each spring thereafter prior to applying broadcast fertilizers. These soil samples were analyzed by the Purdue Soil Testing Laboratory. At the beginning of this experiment the pH was 6.7, P was 63 pounds per acre (medium), and K was 191 pounds per acre (medium).

Three rates of P and three rates of K were broadcast each spring. In 1962 these fertilizers were broadcast and disked in, and in later years they were broadcast and plowed under. In the P experiment with
soybeans, K was applied to all plots at 50 pounds per acre each year, and in the K experiment P was applied to all plots at 26 pounds per acre each year. No commercial nitrogen was applied to any plot or any treatment.

The Lindarin variety of soybeans was seeded in 1962 and 1963, and Harosoy 63 was seeded in 1964 and 1965. The rate of seeding was about one bushel per acre in rows 28 inches apart. Either four or six center rows of an eight-row plot 100 feet long were harvested with a self-propelled farm combine. Yields of grain were reported on a 13 per cent moisture basis. For the 1962 plant analyses, 10 plants from the center six rows of each plot were selected. The entire above ground part of the plant was ground for chemical analyses. These samples were analyzed by the Ohio Plant Analysis Laboratory, Wooster, Ohio.
The phosphorus and the potassium experiments were each arranged in a complete randomized block design with three replications.

PURDUE UNIVERSITY • Agricultural Experiment Station • Lafayette, Indiana