Masters Theses

Date of Award

5-1990

Degree Type

Thesis

Degree Name

Master of Science

Major

Plant, Soil and Environmental Sciences

Major Professor

William A. Krueger

Committee Members

Neil Rhodes Jr., Elmer Ashburn

Abstract

Field and greenhouse experiments were conducted in 1988 and 1989 to determine the influence of soil pH on the persistence of imazaquin (2- [4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-lH-imidazol-2-yl]-3- quinolinecarboxylic acid), imazethapyr ± (2-[4,5-dihydro-4-methyl-4-(1- methylethyl)-5-oxo-1H-imidazol-2yl]-5-ethyl-3-pyridinecarboxylic acid), and chlorimuron (2-[[[[(4-chloro-6-methoxy-2-pyrimidinyl)amino]carbonyl]amino]sulfonyl]benzoic acid). The concentrations were determined by using a standard response curve comparing the radicle length of corn 'Pioneer 3369A', treated with a known concentration of each herbicide, to the radicle length of corn from the treated areas in field samples.

Field studies were conducted at three locations in Tennessee representing West, Middle, and East Tennessee. The initial soil pH at all locations was 4.9 to 5.2. Soil pH was altered to 5.2, 5.5, 6.5, and 7.2 using hydrated lime (Ca(OH)2) . Herbicide treatments included imazaquin at 0.14 kg ai ha-1, imazethapyr at 0.07 kg ai ha-1, and chlorimuron-ethyl at 0.05 kg ai ha-1. The experimental design used was a randomized complete block with a split-plot factorial arrangement of treatments, each replicated four times. The pH's were assigned to the main plots and herbicides were assigned to the split plots. All herbicides were incorporated using a field cultivator with S-tines followed by revolving baskets. Soybeans 'Asgrow 5474' were planted at all locations. Soil samples were taken 0, 8, 16, 32, 64, and 128 days after initial application. The soil samples were placed in a freezer and were used in the greenhouse portion of this experiment. The soil was allowed to air dry for 24 h, screened, and then placed in an acetate tube (15.24 cm in length). The tube was capped, placed in a tray filled with water and was allowed to sit for approximately one hour before planting pregerminated seed. Regression analysis was then performed for all herbicides at all locations with concentrations being regressed against time.

Results from the greenhouse bioassay indicate that soil pH significantly affected herbicide persistence. Imazaquin appears to be affected more by low soil pH than does imazethapyr. However, both herbicides dissipate quite rapidly from 0 to 32 days after application. There appears to be no significant difference in imazaquin persistence at pH 5.2 or 5.5. Imazethapyr appears to be more persistent when soil moisture is limited. Chlorimuron proved to be more persistent at pH 7.2 than at any other pH. Soil moisture conditions in 1989 were very high at all locations. Imazethapyr dissipated or moved out of the top 15 cm within 64 days. Crop injury was observed in 1989 with all herbicides. Rainfall occurred shortly after application and appears to have increased the amount of herbicide in the soil solution, making it more readily available for uptake by soybeans.

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