Farmers may be able to increase corn yields by splitting their nitrogen applications, but they could help the cause considerably if they can water the nitrogen in, LSU AgCenter researchers say.
Studies at the Northeast Research Station near St. Joseph, La., and other locations have shown growers can apply supplemental nitrogen as late as tassel emergence and improve yields. But the amount of increase can vary by soil type, year and whether the field can be irrigated.
Last year, LSU AgCenter scientists at the station applied 0, 150, 180, 210, 240 and 270 pounds of nitrogen at the two-leaf growth stage and followed that with 0 or 60 pounds of N (ammonium nitrate) at tasseling to corn planted on a Sharkey silty clay.
Speaking at the Northeast Station's annual field day, Mascagni said researchers at the station have been conducting studies using precision agriculture technology — with a twist.
The monitoring tools include the GreenSeeker optical sensing and variable-rate application system, SPAD or chlorophyll meter and pulling leaf samples to determine total N in the leaf tissues.
That year, researchers applied 180, 210 and 240 pounds of nitrogen in a 32 percent URAN-solution. The nitrogen was knifed in at the two-leaf stage. At tassel emergence, the researchers broadcast 0, 30 or 60 units of nitrogen as ammonium nitrate.
The researchers applied 120 pounds and 180 pounds of nitrogen per acre to a Commerce silt loam soil in a non-irrigated test that same year. Yields ranged from 155 to 200 bushels per acre, but produced no significant differences between single and split applications.
In 2006, the researchers encountered some yield differences between the two methods in a non-irrigated and irrigated test. Planting a different hybrid, Pioneer 31R88, the researchers applied rates of 150, 180, 210, 240 and 270 pounds of nitrogen at the two-leaf stage. Late applications included 0 or 60 pounds of N as ammonium nitrate.
In the irrigated plots, applying 60 pounds of nitrogen at tassel emergence increased the yield with the 150-pound early season rate from 148 bushels (with 0 late N) to 178 bushels per acre.
"Nitrogen moves with the soil water to the roots via mass flow," he said. "If you don't have any soil water, then nitrogen is not being transported to the roots. The plant itself is also being affected, shutting down somewhat in the heat resulting from the lack of moisture.
Researchers took seed samples and had them analyzed for the percentage of nitrogen and total seed nitrogen. They also calculated nitrogen fertilizer uptake efficiency percentages for the different rates of early season and late season nitrogen applications and correlated those numbers with grain yields.
Irrigation is proving to be a key ingredient in this year's tests, as well, he noted.
"We've watered this test about four times," said Mascagni, who spoke in front of the irrigated plots in the Sharkey clay portion of the study at the field day on June 13. "Our last rain was about 1.3 inches on May 3. That's been about 40 days we basically have had no rain. The non-irrigated corn is really starting to show the effects of drought stress.
Mascagni said the researchers will attempt to harvest the plots and continue to analyze the data from the GreenSeeker technology, SPAD meter and leaf and seed samples.