Enhance Economic Opportunities for Agricultural Producers
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 in 2001 those costs rose approximately
30 percent and more or less remained at that level during 2002 and 2003.
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 at
three UA agricultural centers. At each location, treatments varied from
a conservative to a more aggressive approach to nitrogen management. Results
at each location revealed a strong relationship between the crop fruit
retention levels and nitrogen needs for the crop. Results showed that the
higher, more aggressive N application regimes did not consistently benefit
yields at any location. Generally, the more conservative, feedback approach
to N management provided optimum yields at all locations.
UA College of Agriculture and Life Sciences researchers have designed
nitrogen management guidelines and recommendations that pinpointed the
best times to apply nitrogen in the proper amounts. Over the last 14 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 2003 nitrogen prices, would be about $15-$25 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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