Preplant spring anhydrous ammonia is the best bet for reducing N loss, says Kyveryga of his on-farm trials. The ISA On-Farm Network used late-season aerial imagery and cornstalk nitrate testing to estimate the size of N-deficient areas within 683 fields in a relatively dry 2006; 824 fields in a relatively wet 2007 and 828 fields in a very wet 2008.

More N from fall manure was required to reach optimal N values in cornstalk tests than from any other N source or timing in each year.

Fall-applied anhydrous ammonia required the second-highest amount of N for optimal cornstalk test status, while spring and sidedress applications consistently required the lowest amount of N. In the extremely wet 2008, most of the stalk samples from side-dressed UAN were N-deficient. But, sidedressing UAN also saved on total N needed to reach optimal cornstalk N values.

There was a higher probability for economic gain from adding more N (achieve an extra 5 bushels an acre from adding 50 pounds of N to manure rates farmers usually use) on manured fields than for any other form. This surprised Kyveryga, even after four years of 125 strip trials that he analyzed from a profit perspective. That was despite the fact that manured fields already had slightly higher N rates applied than any of the other N forms.