Doctoral Dissertations

Date of Award

3-1975

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Plant, Soil and Environmental Sciences

Major Professor

William L. Parks

Committee Members

L. F. Seatz, F. F. Bell, J. I. Sewell

Abstract

This investigation was conducted for two seasons (1972 and 1973) on a Sequatchie loam soil at the Plant Science Farm, Knoxville, Tennessee. The effect of bulk density and large pore space on root distribution, nutrient absorption, and yield of corn and soybeans planted at different row arrangements was studied. Bulk density, large pore space and root volume from soil core samples taken at different distances from the reference row at different times were measured. The amount of plant roots per unit volume of soil gradually increased as the season progressed but decreased late in the season in both corn and soybeans. Root volume data from samples taken at comparable distance from the reference row showed that row arrangement had no effect on root volume for corn and soybeans during both years. Higher bulk density and smaller percentage of large pore space at the 6-12-inch depth generally impaired root penetration by soybean plants, but had less effect on root penetration by the corn plants. The root volume in the surface soil was generally higher close to the row and decreased gradually as the distance from the row increased. Above ground plant samples taken at different times during the growing season were analyzed for their concentration of N, P, K, Ca, and Mg. Generally the nutrient percentages in the above ground corn plants were high early in the season and decreased as the season progressed except for P which was high early in the season, decreased up to 60 days, and then leveled off in 1972 but increased to higher than the original levels in 1973. The nutrient percentage means for all row arrangements followed the same pattern and generally were not statistically different except for the period from tasseling to filling stage of growth in the 12-24" row arrangement in 1972. N, P, K, Ca, and Mg accumulation in pounds per acre gradually increased up to about 70 days (tasseling stage). During the ear development and filling stage of growth the amount of N, P, and K greatly increased while the increases in Ca and Mg were very small. In soybeans, N, P. K, Ca, and Mg percentages were higher in the early stages of growth. Percentage of N and P generally decreased for about the first 70 to 80 days after planting and then increased slightly while the percent of K decreased as the season progressed. Ca and Mg percentages tended to level off at a later stage of growth. The amount of N, P, K, Ca and Mg that accumulated in the above ground soybean plants increased gradually for about 70 days. After this period a large increase in content of N and K was observed while the increase of P, Ca and Mg was less pronounced. Root volume did not account for any yield differences among the row arrangements in corn and soybeans in either year. Corn at 17,424 plants per acre in 1972 produced a lower yield than 20,380 plants per acre in 1973. At the lower plant population in 1972, row arrangements did produce significantly different yields. However, at 20,380 plants per acre in 1973, row arrangement had no effect on corn yield. Irregular soybean plant distribution and large percentage of lodging occurred in 12" and 12-24" row arrangements which reduced the yield of these treatments and may have accounted for no yield differences among the row arrangements.

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