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Competitive Agricultural Systems in Global Economy
Nitrogen Management in Irrigated Cotton
Issue
The traditional approach to nitrogen management in irrigated cotton
has been to push for maximum high yields by applying large amounts of
nitrogen fertilizer. Historically, in many parts of Arizona, nitrogen
application rates have exceeded 200 pounds per acre per season. Although
yields may increase, there are serious drawbacks to this practice. Over
the last 10-15 years the luxuriant vegetative growth resulting from
these high nitrogen applications has harbored damaging insect populations
and diseases in Arizona's cotton fields. Studies during the same period
have shown that aggressive nitrogen fertilizer application can actually
increase the loss of nitrogen from the soil. In the past, nitrogen fertilizer
has been relatively inexpensive for Southwest desert growers, but early
in 2001 those costs rose approximately 30 percent, where they remained
throughout 2002.
What has been done?
To help Arizona cotton growers reduce their reliance on high nitrogen
applications in their fields, University of Arizona researchers studied
and documented nitrogen uptake patterns and requirements in the crop.
UA College of Agriculture and Life Sciences researchers then designed
nitrogen management guidelines and recommendations that pinpointed the
best times to apply nitrogen in the proper amounts. Over the last 13
years this comprehensive nitrogen management strategy has been implemented
in a statewide extension education plan for cotton growers that includes
bulletins, reports, articles and grower meetings.
Impact
The cost of cotton production has been high during the last several
years, but the market price has been low. UA demonstration projects
on cooperating cotton farms have realized yields equivalent to commercial
yields, using less nitrogen input, which has saved approximately $30
per acre in nitrogen application costs. If adopted statewide, the annual
savings, at February 2002 nitrogen prices, would be about $15-$20 per
acre. If 200,000 acres of the total cotton acreage in Arizona were affected,
this would equate to $3 to $4 million in savings to the growers. Growers
would be using approximately 150 pounds per acre, compared to a more
common rate of about 200 pounds per acre, a 25 percent reduction. In
200,000 acres of cotton, this means 5,000,000 pounds of nitrogen fertilizer
would be withheld, resulting in less rampant vegetative growth, fewer
insect problems and improved plant use of residual nitrogen in the soil.
It would also protect groundwater from excess leaching of nitrogen compounds,
thereby protecting the environment.
Difficult market conditions, which are the worst they've been since
the Great Depression, have no doubt served as a stimulus in encouraging
growers to make these changes. Approximately 60 percent of the cotton
growers in Arizona are using more conservative nitrogen management strategies
than they were five to ten years ago. Fortunately, the information in
the educational program associated with these management decisions was
already in place.
Funding
Water Quality Program, national Cooperative Extension Hatch Act
Smith-Lever
Arizona Cotton Growers Association; Cotton Incorporated
Contact
Jeff Silvertooth, professor and head
Department of Soil, Water and Environmental Science
429 Shantz Bldg, #38
College of Agriculture and Life Sciences
The University of Arizona
Tucson, AZ 85721
Tel: (520) 621-7228, FAX: (520) 621-1647
Email: silver@ag.arizona.edu
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