Researchers from Washington and Connecticut are seeking to improve corn nitrogen (N) recommendations to the point that recommendations can be made on a field-by-field basis.
The two most common current corn N recommendation methods are the Yield Goal Method and the Maximum Return to Nitrogen (MRTN) method—the method currently used by Michigan State University Extension. These methods are good for achieving profitable yields, on average, across many fields and years, but they are not suited—or intended—for field-specific recommendations.
In “Factors Affecting Nitrogen Availability and Variability in Cornfields,” published Aug. 16, 2018, in the Agronomy Journal, the researchers noted the promotion of the “4Rs of Nutrient Stewardship” concept: right source, right rate, right time and right place.
To develop this model, the researchers used aerial imagery and digital soil maps to guide cornstalk sampling for the Cornstalk Nitrate Test (CSNT)—a reliable end-of-season evaluation tool for corn N status. The researchers started with a two-year study conducted on 683 fields in Iowa, and expanded it to include 920 more fields in Illinois, Indiana, Ohio and Michigan from 2008 to 2014.
The researchers took aerial imagery of these fields in mid- to late August each year. Guided by USDA-NRCS digital soil maps, and aerial imagery, the researchers selected four sampling areas in each of the 920 fields for a total of 3,680 cornstalk sampling sites. The researchers identified three predominant soil types in each field.
Almost half (43 percent) of the fields in the study received N rates between 150–200 pounds per acre, and 78 percent of fields received N rates between 150–250 pounds per acre. Most farmers applied N as a sidedress between V3 and V6 in the form of anhydrous ammonia (24 percent) or urea ammonium nitrate (43 percent). About 19 percent of fields received a fall application of anhydrous ammonia, and the remainder of the fields received spring anhydrous (6 percent) or UAN (8 percent).
Most of the fields were managed as soybean-corn rotations, some were corn-corn and others were wheat-corn. Seventy-six percent of the fields were tilled using strip tillage or chisel tillage in the spring or fall, and 24 percent were no-till.
Ultimately, the researchers learned that three types of factors had significant effects on N sufficiency levels.
To find out what he three factors were and the effects on N sufficiency levels, check out the story from Michigan State University here.