Masters Theses

Date of Award

3-1981

Degree Type

Thesis

Degree Name

Master of Science

Major

Plant, Soil and Environmental Sciences

Major Professor

W. L. Parks

Committee Members

L. N. Skold, F. F. Bell

Abstract

‘Essex' soybeans (Glycine max (L.) Merr.) were used to investi-gate how the relationship between plant density and distribution and environmental weather factors such as radiation, temperature and soil moisture influences soybean yield. Field studies were conducted during the 1980 growing season on a Sequatchie loam soil at the Plant and Soil Science Field Laboratory near Knoxville, Tennessee. Soybean yields were measured at plant populations of 2, 4, 6, 8, 10, and 12 plants per 30 cm of row in 25 cm, 51 cm, 76 cm, and 102-cm rows. Soil moisture depletion was measured by neutron meter in the middle of the row and adjacent to the row to determine the pattern of soil moisture as affected by different plant populations and row spacings. Incoming radiation was measured at the top of the plant canopy and down vertically in the middle of the row and over the main axis of the plant. Vinyl tipped waterproof probes were used for soil tempera-ture measurements at 8 plants per 30 cm of the row for 25, 51, and 76- cm row spacings. As an average of all plant populations the highest yields were obtained from the 25-cm row spacing. Among plant populations, the yield for 2 plants per 30 cm of row was the lowest regardless of the row spacing. Interactions of the number of plants and row spacings showed that the 25-cm row spacing with 8 or 10 plants per 30 cm of row generally outyielded all other planting patterns. Percent surface soil moisture early in the season was very similar for all planting patterns. Later in the season the pattern of soil moisture was indicated that regardless of row spacing, moisture use in the row was higher than in the middle of the row. Moisture content in wider rows (76, 102 cm) was higher than in narrower rows probably because of less competition among plants to exploit surface moisture and larger area between rows. Yields were reduced in relation to the reduction in surface soil moisture. Soybeans which were grown in narrow rows had a significant effect on solar interception. Number of plants per 30 cm of the row was not as influential on light interception as row spacings. The percent of radiation reaching the soil surface in the middle of the row increased with row width. During the day early in the season at full canopy closure there was no significant difference between middle-of-the-row and in-the-row soil temperatures at 25-cm row spacing. The soil temperature reached its maximum value about 2 hours after the maximum air temperature. Soil temperature difference at time of canopy closure was not significant between the 25-cm and 76-cm row spacings.

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