Masters Theses

Date of Award

6-1977

Degree Type

Thesis

Degree Name

Master of Science

Major

Plant, Soil and Environmental Sciences

Major Professor

Larry S. Jeffery

Committee Members

Vernon H. Reich, Elmer L. Ashburn

Abstract

Tennessee farmers and researchers have experienced occasional soybean (Glycine max) injury when chlorbromuron [3-(4-bromo-3-chlorophenyl)-1- methoxy-1-methylurea], linuron [3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea], and metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazine- 5(4H) one] have been applied for preemergence weed control in soybeans. The activity of these herbicides on various soils needs to be understood in order to obtain effective weed control without causing soybean injury. Field studies were conducted during 1976, at three locations in Tennessee on seven soil types. The objectives of this study were to determine soybean response to various rates of chlorbromuron, linuron, and metribuzin, to determine the maximum rate that can be applied to a specific soil without reducing soybean yield and to correlate the most effective rate of chlorbromuron, linuron, and metribuzin for weed control and soybean tolerance to the physical properties of a soil. The herbicides were applied preemergence at the following rates: chlorbromuron at 1.7, 2.3, 2.8, and 3.4 kg/ha; linuron at 0.6, 0.8, 1.1, and 1.7 kg/ha; and metribuzin at 0.3, 0.4, 0.6, and 0.8 kg/ha. The soils studied were Captina clay loam, Sequatchie sandy loam, Sequatchie loam, Hartsells loam, Falaya-Collins silt loam, Ocklochonee loam, and Loring silty clay loam. The experimental design was a modified factorial arrangement of a randomized complete block design with four replications. Data were obtained on soybean vigor reduction, stand reduction, plant height, forage weight and yield on the four East Tennessee soils. No data on plant height and forage weight were obtained on the three West Tennessee soils. Early chlorbromuron injury, as noted by soybean vigor and stand reduction ratings taken early in the growing season, was later expressed in reduced soybean yields on all rates applied on Falaya-Collins silt loam (0.3-1.5x the highest recommended rate). Rates greater than 1.7 kg/ha caused early injury and reduced yields on Ocklochonee loam (1-1.5x the highest recommended rate) and Loring silty clay loam (0.8-1.2x recommended rate) and rates greater than 2.3 kg/ha caused early injury and reduced yields on Sequatchie loam (1.2-1.5x highest recommended rate). None-to-slight injury occurred at the highest rate of chlorbromuron on Captina clay loam (1.2x highest recommended rate) and Sequatchie sandy loam (2x highest recommended rate) but no reduction in yield occurred. No injury or yield reduction occurred on Hartsells loam (0.5-1.0x recommended rate). Early linuron injury at the 1.7 kg/ha rate occurred on Sequatchie sandy loam and Sequatchie loam (1.3x highest recommended rate for both) but no reduction in yield occurred. Yields were reduced when the 1.7 kg/ha rate was applied on Falaya-Collins silt loam and Ocklochonee loam (1.3x recommended rate for both). No injury occurred at any of the rates used on Captina clay loam (0.4-1.1x highest recommended rate), Hartsells loam (0.3-0.7x highest recommended rate), and Loring silty clay loam (0.4-1.1x highest recommended rate). Early metribuzin injury and reduced yields occurred when the 0.8 kg/ha rate was applied on Falaya-Collins silt loam (2x Du Font's recommended rate and 1.3x Chemagro's highest recommended rate) and on Loring silty clay loam (1.1 Chemagro's and 1.4x Du Font's recommended rate). Early injury with no yield reduction occurred at the 0.4 and 0.6 kg/ha rates on Falaya-Collins silt loam (1-1.5x Du Font's recommended rates and Ix Chemagro's recommended rate), at 0.6 and 0.8 kg/ha rates on Ocklochonee loam (1.5-2x Du Font's recommended rates and 1-1.3x Chemagro's highest recommended rates), and at 0.4 and 0.6 kg/ha on Loring silty clay loam (0.7-1x Du Font's recommended rate and 0.6-0.9x Chemagro's recommended rates). Injury on Captina clay loam occurred at the 0.6 and 0.8 kg/ha rates (1-1.4x Du Font and 0.9-1.1x Chemagro's recommended rates), on Sequatchie sandy loam at 0.8 kg/ha (both companies do not recommend use) and at the 0.8 kg/ha rate on Sequatchie loam (2x Du Font and 1.3x Chemagro's recommended rates). No injury or yield reduction occurred at any of the rates used on Hartsells loam. However, at the 0.4 kg/ha rate, yields were found to be increased over the check. This rate was 0.7x that recommended by Du Font and 0.6x that recommended by Chemagro. Correlations between soil properties, injury, and yield show that organic matter content and pH have the greatest effect on buffering , phytotoxic effects. Similarly, the stepwise multiple regression analysis procedure showed that organic matter and pH accounted for most of the variation of all of the variables studied.

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