Cotton Agriculture -- Southern United States
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.
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.
Specifically, the goals of the research are:
- to compile and map the current use of pesticides across the cotton
- 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.
This investigation is being conducted by the Kansas
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).
- Gianessi, L.P., and Puffer, C., 1990,
- Herbicide use in the United States: Resources for the Future, National
- Meyer, M.T., 1995,
- Geochemistry of cyanazine and its metabolites: University of Kansas,
Ph. D. Thesis, 362 p.
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