Spring soil nitrogen following the drought of 2012
We don’t have many direct measures of how much ammonia applied in the fall of 2012 is still present, but based on a few estimates, we believe that loss of NH3 applied in fall 2012 has been relatively small. One field that Dan Schaefer sampled in October 2012 had 11.5 and 7.6 ppm of nitrate-N, and 3.7 and 2 ppm of ammonium-N in the top and second foot, respectively. In November, 100 lb of N as NH3 was applied. March samples showed 6.5 and 11 ppm nitrate-N and 12.7 and 2.4 ppm of ammonium-N in the top and second foot, respectively. Probe samples from the application band are not a very reliable way to measure N, but if we assume a 35-lb loss of nitrate-N (average of the other two fields described above), the probe sample “found” about 2/3rds of the N that was applied last fall, and about half of that remains in the ammonium form. Compared to some fall-to-spring changes in ammonium-N reported in the literature, we think that nitrification (conversion of ammonium to nitrate) and loss of fall-applied N have been less than normal this winter.
Other sampling done over the past month, in some cases to see if winter wheat should have N topdressing rate adjusted, has shown nitrate-N to be fairly low, often less than 5 or 6 ppm. The winter wheat crop would not have taken up much N when samples were taken, but soil nitrate-N does drop by 1 ppm for each 4 lb. of N present in the wheat (or other) crop at the time of sampling.
Spring Sampling, 2013
The priority for spring sampling should be those fields where corn in 2013 will follow corn (from which fall samples were taken) in 2012. We suggested last fall that any spring sampling done in order to adjust rates for the 2013 corn crop should best be done close to corn planting time, or at sidedress time. However, it would be useful if at least some of those sites where fall soil N levels were high could be sampled within the next few weeks so that we could better guess how much additional sampling would be useful.
I suggest that sites with fall nitrate-N above 25 ppm nitrate-N in the top foot (that is about 25% of Illinois sites) be sampled first, but any and all sites can be re-sampled if volunteers are willing to do this. All those who coordinated sampling last fall and who requested forms and shipping materials through me will get an email in the next few days with brief instructions. The process will be the same as it was last fall, with samples sent to A&L for analysis, and funding provided through C-BMP. Those who sampled under GROWMARK’s direction last fall will continue in that program this spring.
Those who did not sample fields last fall but would like to do so this spring are also invited to participate. Instead of sending requests through me, however, we ask that those sampling this spring for the first time send requests to Jean Payne firstname.lastname@example.org at the Illinois Fertilizer & Chemical Association, who will pass along the request for sampling materials and instructions.