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Cotton Agriculture -- Southern United States

Introduction

cotton-map-sThe application of pesticides to cotton (Gossypium hirsutum) is an important issue that affects the water quality of the southern United States. Cotton receives as much as 7 kilograms per hectare of herbicide and 5 kilograms per hectare of insecticide (Gianessi and Puffer, 1990). The heavy application of pesticides is required, especially in the humid south where weed pressure is great and the boll weevil (Anthonomus grandis) is a major insect pest. These applications of pesticides are 3 to 5 times greater per hectare than applications of pesticides to corn, yet there have been no regional studies of pesticide fate in the cotton belt.

The cotton belt includes the states of Arkansas, Louisiana, Mississippi, Texas, Arizona, and California. Lesser amounts of cotton are grown in the states of North and South Carolina, Georgia, Alabama, and New Mexico. These eleven states make up an area known as the "cotton belt." There are five "hot spots" of cotton production: the Mississippi Delta, the high plains of West Texas, the southern tip of Texas, the arid desert region of southwest Arizona, and the Southern Valley of California. These "hot spots" are in vastly different climatic regimes. They have different precipitation amounts, weed pressures, and runoff and leaching potentials. Because of these considerations the types of herbicides vary considerably.

The major herbicides applied across the cotton belt are: trifluralin, monosodium methanearsonate (MSMA), disodium methanearsonate (DSMA) (organic arsenicals), fluometuron, prometryn, cyanazine, pendimethalin, norflurazon, and diuron, and the major insecticide is methyl parathion. Together, these ten compounds account for the majority of pesticides that impact the cotton belt. With the exception of cyanazine (Meyer, 1995), no detailed studies of these compounds have been conducted at the field and basin scale. Thus, unlike the corn belt, there is a gap in our knowledge of the transport and fate of cotton pesticides and their metabolites.

The Problem

Because large quantities of pesticides are applied to cotton over a vast region of the southern United States and our understanding of pesticide transport and fate is poor, there is an immediate need for an integrated study of the fate of cotton pesticides.

This investigation will examine key findings from the study of agricultural chemicals in the Midwest concerning pesticide use, chemical structure, and hydrology in order to develop an integrated strategy for identifying the important questions in the cotton belt with respect to transport, fate, and possible toxicity of pesticides and their metabolites. Special emphasis will be given to the critical processes involved such as sorption, volatilization, decomposition, and transport.

The questions being asked do not deal with specific basins, but rather deal with land use and chemical and physical processes. Development of specific analytical methods is required for several of the heavily applied herbicides, such as the organic arsenicals, and pesticide metabolites in general. This study will provide synthesis of important questions on the processes of decomposition, transport, and fate.

Objectives

Specifically, the goals of the research are:

  • to compile and map the current use of pesticides across the cotton belt,
  • to determine which pesticides and their metabolites enter surface and ground water of the cotton belt and to develop models to predict their occurrence, and
  • to use the knowledge from studies of the corn belt to examine the most critical geochemical processes that affect the fate, transport, and toxicity of cotton pesticides in surface and ground water.

Research Team

This investigation is being conducted by the Kansas District, Organic Geochemistry Research Group, which is based in Lawrence, Kansas, and is being coordinated with the activities of the Mississippi Embayment Study Unit of the National Water-Quality Assessment Program (NAWQA).

Related Headlines

More Information

References

Gianessi, L.P., and Puffer, C., 1990,
Herbicide use in the United States: Resources for the Future, National Summary Report.
Meyer, M.T., 1995,
Geochemistry of cyanazine and its metabolites: University of Kansas, Ph. D. Thesis, 362 p.

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