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The proper management of nitrogen is critical to
the success of many crop systems. Based on an assessment of the
natural amount of nitrogen in soil, growers calculate their optimum
nitrogen rates, the concentration of nitrogen that must be present in
fertilizer in order to achieve expected crop yields. Under- and
over-applying nitrogen fertilizer to corn crops often leads to adverse
economic consequences for corn producers. Excess levels of nitrogen in
nature also pose serious threats to environment. Agricultural
application of nitrogen has been linked to rising nitrate levels and
subsequent death of fish in the Gulf of Mexico and North Carolina’s
Neuse River.
"Although offsite nitrogen contamination of ground
and surface waters could be reduced if nitrogen rates were adjusted
based on actual field conditions, there is currently no effective soil
nitrogen test for the humid southeastern U.S.," said Jared Williams,
lead author of the North Carolina State study that was published in
the March-April 2007 issue of the Soil Science Society of America
Journal. This research was supported in part by USDA Initiative for
Future Agricultural and Food Systems (IFAFS) grant.
From 2001 to 2004, scientists collected and tested
the soil from 35 different sites in North Carolina. According to the
North Carolina scientists, the collected soil samples were
representative of millions of hectares in agricultural production in
the southeastern USA. Corn was planted at each site with a range of
nitrogen fertilizer rates, and the optimum nitrogen rates and the soil
assay results were compared among the sites.
From the collected samples, researchers discovered
that the Illinois Soil Nitrogen Test (ISNT) could be used to
accurately measure the economic optimum nitrogen rates (EONR) of
southeastern soils, despite moderate weather variation over the
collection period. While the test can be used to predict the optimum
nitrogen rates, the relationship between ISNT and EONR varied by soil
drainage class. Researchers believe that these differences represent
differences in organic matter that lead to less mineralization and/or
more denitrification on poorly drained soils. The results indicate
that the Illinois Soil Nitrogen Test can serve as a model for
predicting economic optimum nitrogen rates on well- and poorly drained
soils and show promise as a tool for nitrogen management.
"Additional research is needed to calibrate and
validate the EONR versus ISNT relationships under a wider variety of
conditions," says Williams. "Because the Illinois Soil Nitrogen Test
predicted EONR robustly to different cost/price ratios, ISNT has the
potential to modify or replace current nitrogen recommendation methods
for corn." |
