Nitrogen deficiency is one of the biggest hurdles when adopting no-till corn production in Wisconsin. Most agronomists would say that ammonia lost from surface-applied urea-containing fertilizers (volatilization) and nitrogen tied up with organic matter in residue (immobilization) are the reasons more nitrogen is needed on no-till corn. However, these explanations are not supported by current research at the University of Wisconsin-Madison.
“Nitrogen deficiency in high-residue systems is probably not due to volatilization or immobilization,” says Larry Bundy, extension soil scientist in the College of Agricultural and Life Sciences.
Bundy found volatilization of ammonia was low with urea-containing fertilizers. He also found that less nitrogen was released from the soil (mineralized) in plots containing residue. This decreased mineralization was due to colder soil temperatures, not immobilization in surface residue.
By comparing fertilizers, he also found that ammonium nitrate is more effective than urea. At a rate of 80 pounds of nitrogen per acre, ammonium nitrate averaged 20 bushels per acre more corn than urea-based fertilizers at that rate. This means a $42 to $46 per acre gain with ammonium nitrate.
Bundy”s advice to farmers using urea-containing fertilizers: inject or incorporate where possible to reduce the risk of ammonia losses. Where corn residue is 50 percent or more, apply an additional 30 pounds of nitrogen per acre. This will offset lower amounts of available nitrogen from decreased mineralization in high residue, he said. Additional nitrogen is not needed in fields with previous crop residues from soybeans or alfalfa.
Bundy studied surface-applied nitrogen fertilizers in no-till corn following corn from 1993 to 1996 at the Arlington Agricultural Research Station. He compared ammonium nitrate, urea-ammonium nitrate, and urea at 80 pounds per acre with different application methods (broadcast, spray, and injection). Soil temperatures were recorded every five hours for the entire growing season.
The researcher applied fertilizers to 10-foot by 30-foot randomized plots, on silt loam soils, containing no residue, normal residue, and twice the normal amount of residue. He also made applications to plots covered with polypropylene snow fence to simulate residue. “The fence doesn”t enter the nitrogen cycle,” Bundy noted. “Plastic duplicated the influence of normal residue regarding soil moisture effects, but without he biological occurrences.”
More research is needed to explain the differences between performance of urea- and ammonia-based nitrogen fertilizers.