Masters Theses

Date of Award


Degree Type


Degree Name

Master of Science


Agricultural Economics

Major Professor

Roland K. Roberts

Committee Members

Burton English, Robert Hayes


In 1994 and 1995 field experiments were conducted at Milan, TN, using Roundup- Ready™ soybeans double cropped with wheat in a no-till planting system. Johnsongrass control chemicals were broadcast applied post-emergence at rates low, medium, high, and very high relative to label rates. The herbicides used were glyphosate (Roundup), quizalofop (Assure 11), fluazifop-P (Fusilade DX), sethoxydim plus an adjuvant (Poast Plus), and clethodim (Select). Roundup was applied at rates of 0.368, 0.736, 1.10, and 1.47 lb a.i./acre. Assure II was applied at rates of 0.025, 0.05, 0.075, and 0.1 lb a.i./acre. Fusilade DX was applied at rates of 0.06, 0.12, 0.18, and 0.24 lb a.i./acre. Poast Plus was applied at rates of 0.08, 0.16, 0.24, and 0.32 lb a.i./acre. Finally, Select was applied at rates of 0.04, 0.08, 0.12, and 0.16 lb a.i./acre. The experimental design was a randomized complete block with plots measuring 10 feet wide by 30 feet long with 30-inch row spacing. Treatments in both years were replicated three times.

he objectives of this study were 1) compare the economic benefits of using Roundup versus alternative herbicides to control johnsongrass on Roundup-Ready™ soybeans and 2) compare profitability of Roundup on Roundup-Ready™ soybeans to alternative johnsongrass control herbicides on other soybean varieties.

Quadratic yield response functions were estimated through regression analysis for each herbicide for the individual years of the experiment (1994 and 1995) and for the combination of the two years (1994-1995). Profit-maximizing rates and yields were calculated for five herbicides using either the estimated yield response function or assuming a constant function based upon two criteria. The first criterion for a significant function was that the Prob>F be less than 0.10 and the second was that there be diminishing physical product. The profit-maximizing rate and yield for each herbicide was then used in enterprise budgets to calculate returns to land, management, and risk.

Roundup proved to be the most cost effective herbicide in an economic comparison of returns achieved with Roundup on Roundup-Ready™ soybeans and those achieved by Assure II, Fusilade DX, Poast Plus, and Select on Roundup-Ready™ soybeans. Roundup was able to achieve the highest returns to land, management, and risk over the four alternative herbicides because of its lower cost and higher yields. Roundup's lower costs are attributed to its ability to control both grasses such as johnsongrass and broadleaf weeds therefore requiring fewer sprays. The four alternative herbicides required an additional herbicide (Storm) for broadleaf control therefore increasing the number of sprays required, which in turn, increase the machinery and labor costs.

Break-even yields for all alternative herbicides were calculated for 1994, 1995, and 1994-1995. These yields are those needed to be achieved by an alternative herbicide on any other variety of soybeans to have equivalent returns to those achieved by Roundup on Roundup-Ready™ soybeans using either Roundup's recommended or profit-maximizing rate. Comparisons were made between the calculated break-even yields and the yields associated with the recommended and profit-maximizing rates of the alternative herbicides. These yields were derived from the estimated yield response functions using the experimental data on Roundup-Ready™ soybeans.

Break-even yields calculated for alternative varieties and herbicides equating their returns to those achieved with the recommended rate of Roundup on Roundup-Ready™ soybeans were all equal to Roundup's yields. These break-even yields were equal to Roundup's yields due to their similar production costs. The break-even yields equating the alternative herbicide's returns to those achieved with the profit-maximizing rates of Roundup on Roundup-Ready™ soybeans ranged from 1 bushel less to 3 bushels greater than yields achieved by Roundup on Roundup-Ready™ soybeans. Comparisons made between the break-even yields and the yields for the recommended rates and profit-maximizing rates of the alternative herbicides on Roundup-Ready™ soybeans based on yield response functions derived from the experimental data, showed that the alternative herbicides did not achieve the break-even yields on Roundup-Ready™ soybeans.

The break-even methodology used in this paper demonstrates that scientists and practitioners can make economically justified recommendations or decisions regarding whether to plant Roundup-Ready™ soybeans without having side-by-side variety trial data to compare net returns. Based on this methodology, farmers would increase their return to land, management, and risk by planting Roundup-Ready™ soybeans if their expected yield from their traditional variety and herbicide were less than the break-even yield. Yields from side-by-side variety trials are important to obtain because they can help farmers develop yield expectations, reducing the uncertainty surrounding the Roundup- Ready™ soybean decision.

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