MADISON, Wisconsin, September 22, 2003, The American Society of Agronomy:
Many producers currently base nitrogen fertilizer applications
on the results of soil nitrate tests. According to a
recent article in the Soil Science Society of America
Journal, farmers can reduce in-season nitrogen use for
irrigated crops without sacrificing yield potential
by using commercially available nitrogen sensing tools.
The typical spring soil nitrate tests do not account
for nitrate loss or gain between soil sampling and planting,
notes Kevin Bronson, associate professor of soil fertility
and nutrient management with the Texas Agricultural
Experiment Station. His study suggests in-season monitoring
may lead to more accurate nitrogen fertilizer recommendations.
Bronson led an interdisciplinary team of scientists
to test in-season nitrogen using monitoring tools at
two irrigated west Texas cotton sites in 2000 and 2001.
Based on spectroradiometer and chlorophyll meter readings,
the team applied 30 pounds per acre of nitrogen in-season
to their plots when indicated at early squaring, early
bloom and peak bloom.
In 2000, they applied 30 to 90 pounds per acre less
nitrogen than a soil-test recommendation of 120 lbs.
per acre and achieved yields similar to plants receiving
120 pounds per acre. In 2001, cotton yields reached
their goal of 2.5 bales per acre.
"In-season nitrogen sensing won't replace spring
soil nitrate tests," Bronson says. "It can,
however, reduce in-season nitrogen fertilizer rates
in low-yielding seasons and it can help match soil test
recommendations for yield potential in high-yielding
seasons. We still recommend pre-plant soil testing to
accurately gauge early season nitrogen needs when plants
are too small to use monitoring instruments, and for
determining nutrient needs besides nitrogen."
In addition to helping producers save dollars by reducing
nitrogen applications, these monitoring tools can help
protect ground and surface waters from nitrate contamination
by reducing the amount of residual nitrate nitrogen
in the soil at harvest, Bronson adds
Tess Chua of Texas A&M is the senior author on
the paper. Co-authors include Jon Booker, Wayne Keeling,
Jim Bordovsky and Robert Lascano, Texas A&M University;
Cary Green and Eduardo Segarra, Texas Tech University;
and Arvin Mosier, USDA-ARS.
Soil Science Society of America Journal (SSSAJ),
is a peer-reviewed, international journal of soil science
published six times a year by the Soil Science Society
of America. SSSA Journal contains soil research relating
to physics; chemistry; biology and biochemistry; fertility
and plant nutrition; genesis, morphology, and classification;
water management and conservation; forest and range
soils; nutrient management and soil and plant analysis;
mineralogy; and wetland soils.