Masters Theses

Date of Award

3-1979

Degree Type

Thesis

Degree Name

Master of Science

Major

Plant, Soil and Environmental Sciences

Major Professor

Gary M. Lessman

Committee Members

R. J. Lewis, M. E. Springer

Abstract

In 1975 and 1976, two experiments involving Molybdenum (Mo) and soybean production were conducted in Tennessee on Collins silt loam. One experiment was a Mo source study which consisted of treatments of a check with no Mo fertilizer or lime, 280 kg/ha of lime banded in the row and no Mo, 35 g/ha of Mo applied as a slurry seed treatment. Mo plus Captan applied to the seed as a powder in the hopper box at planting time, and 6.7 metric tons/ha of lime broadcast. The other experiment was a Mo rate study which consisted of slurry seed treatments of Mo at the rates of 0, 7, 14, 21, 28, and 35 g/ha. In 1977, a separate study of lime and Mo rates was conducted on Loring silt loam using two varieties of soybeans, Essex and Bragg. The lime was applied at three rates to produce three soil pH levels with average pH values near 5.2, 5.9, and 6.5. The Mo rates were 0, 200, and 800 g/ha. The objective of this research was to determine the effects of the selected rates of lime and the selected rates and sources of Mo on the availability of soil Mo and the yield and chemical composition of soybeans.

The data from the two earlier experiments consisted of leaf Mo and N concentrations and soybean yields, while the data of the second consisted of these variables plus leaf Mn concentrations, available soil Mo and exchangeable soil Mn concentrations, and soil pH values. The data from the Mo source study revealed that in both years, only the broadcast lime and the slurry seed treatments produced higher leaf N values than the check, but were not different from each other at the 0.05 probability level. With regard to soybean yield, all of the Mo sources tested, with the exception of the banded lime treatment in 1975, produced higher yields than the check, with the slurry seed treatments being responsible for the highest yields in both years. The Mo rate study revealed that in 1975, only the 21 and 35 g/ha Mo rates resulted in leaf Mo values that were higher than the check. It was also found that all of the rates tested in 1975 produced higher leaf N concentrations than the check, with the 14, 28, and 35 g/ha rates yielding the highest values, In both years, all Mo rates produced higher soybean yields than the check. Both varieties from the 1977 lime and Mo rate study revealed that of the variables tested, only the lime treatments produced differences. With the Essex variety, the highest lime rate produced the largest leaf N, soil Mo, and soil pH values and the lowest leaf and soil Mn values. With regard to the Essex soybean yields, all lime rates produced increases in soybean yields over the no lime rate. With the Bragg variety, the highest lime rate resulted in higher leaf N and soil pH values and lower leaf and soil Mn values than were produced by the zero and medium lime rates. An attempt was also made to correlate plant Mo and N concentrations with soybean yields.

Results of these experiments indicate that the slurry seed application of Mo at any of the rates tested increased soybean yields on some unlimed acid soils in Tennessee. It was concluded that soybean yields responded little to soil applied Mo where lime was also added. In addition, leaf content of Mo was found to be an inaccurate indicator of the Mo needs of soybeans.

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