Source: North Dakota State University
By Walt Albus, Leonard Besemann and Heidi Eslinger
Farmers can use high-tech tools to find the nitrogen rates needed to increase yields, say researchers at North Dakota State University.
"Determining nitrogen sufficiency in time is important to achieve nitrogen efficiency," say the researchers, who've been studying the issue since 2007 at the Oakes Irrigation Research site near Oakes, N.D.
"Determining nitrogen sufficiency in time is important to achieve nitrogen efficiency..."
— North Dakota State University
Remote sensing utilizing aerial photography, a Holland Crop Circle ACS 430 active-canopy sensor and a Minolta SPAD 502 chlorophyll meter were tested to determine ability to measure nitrogen sufficiency in 2010 research, which built on research results of previous years.
"Increasing nitrogen rates increased grain yield, chlorophyll meter readings, normalized difference red edge and grain protein," the researchers say. "Light-reflectance measurements decreased with increasing amounts of nitrogen because dark-green plants absorb more red light than light-green plants.
"Remote sensing by chlorophyll meter, Crop Circle Sensor or aerial photography did well in predicting corn-nitrogen status."
Treatments in the ongoing study are spring strip-tilled to an 8-inch depth. Nitrogen is applied in split applications of 65 pounds per acre at planting, with the remainder sidedressed at 150 and 200 pounds per acre.
The low nitrogen treatment receives 20 pounds of nitrogen at planting. Placement is addressed by applying the planting-time nitrogen application with the strip-till operation prior to planting, or dribbling it 3 inches to the side of the seed furrow at planting.
"In prior years, fertilizer nitrogen rates and placement-at-planting and sidedress methods resulted in subtle, but apparent nitrogen deficiencies in the 150- and 200-pound treatments before the sidedressed nitrogen was accessible to the corn plants," the researchers say. "It may be that surface residue immobilized the broadcast application of 50 pounds per acre of nitrogen as UAN (the first nitrogen split) at planting.
"The remaining nitrogen for the 150 pounds per acre and 200-pounds-per-acre treatments (the second split) was applied as a sidedress application in every other row."
Placement and nitrogen-rate issues were addressed in 2010 by increasing the initial application (first nitrogen split) of fertilizer nitrogen to 65 pounds per acre (except for the low nitrogen rate) and knifing between every row in the sidedress treatments.
All plots were spring strip-tilled at an 8-inch depth. Ten gallons per acre of 10-34-0 were applied in this field operation, which was 12 pounds of nitrogen per acre.
The placement of the 10-34-0 was shallower than planned — about 2 inches deep — and caused concern about possible detrimental effects on germination. Evidently, the seed never got in contact with the fertilizer or it was diffused, as there was no observed damage.
The treatment of 20 pounds of nitrogen per acre received another 8 pounds of nitrogen per acre sprayed in a 5-inch band over the seed row after planting as ammonium thiosulfate.
The remainder of the first nitrogen split in the 150- and the 200-pound-per acre treatments was applied at a 6-inch depth with strip-till as 45 pounds of nitrogen per acre as UAN and 8 pounds of nitrogen per acre as ammonium thiosulfate.
The previous treatments of 50 pounds per acre and 100 pounds per acre of nitrogen in 2009 were changed in 2010 to 150 and 200 pounds of dry nitrogen. The remainder of the first split-applied was 45 pounds of nitrogen per acre as UAN, and 8 pounds of nitrogen per acre as ammonium thiosulfate, applied in a surface dribble, 3 inches to the side of the seed row at planting.
The second nitrogen split in the treatments of 150 and 200 pounds of nitrogen and 150 and 200 pounds of dry nitrogen per acre was applied as UAN at sidedress between every row at a 3-inch depth.
The trend for the treatments of 100 and 200 pounds dry nitrogen fertilizer per acre to yield more than their counterparts of 150 and 200 pounds of nitrogen is due to their being planted on previous treatment plots of 50 and 100 pounds per acre of nitrogen where there was significantly less residue.
This is verified in the light reflectance data taken on July 1, in which there is more difference between the placement — strip-till vs. dribble — than there is between the nitrogen rate.