Yesterday's item showed promising results for applying fertilizer as late as the 13 to 15 –leaf stage. If you apply it correctly, even with a high-clearance rig with disks that inject it, or even with drop booms and nozzles, you can still recover the bulk of the yield potential that the field carried in the first place.
That's if weather conditions are right. Purdue University soil fertility specialists Bob Nielsen and Jim Camberato say a big asterisk needs to be added to that situation. There are times when it simply doesn't pay to apply larger amounts of N than the likely response will justify.
The most common situation is when N deficiency is due to saturation of soils and ponding, the specialists note. Even if the ponding and saturation of soils occurred earlier in the season and it's not the case when you're ready to apply fertilizer, the damage may have already been done to the corn plant factory.
Root damage caused by excessive soil moisture may prevent plants from utilizing as much nitrogen, even if it suddenly becomes available. The result of damaged roots is that even if you apply a lot of N late, you may not see the results you were hoping to see.
Many years ago, Dave Mengel, former Purdue University soil fertility specialist, working with Sylvie Brouder, still at Purdue, but now working more in environmental studies within the agronomy department, tested various rates under these kinds of conditions.
Their conclusion was that it might not pay to apply more than 60 pounds per acre if plants were stressed early, or are being stressed by winds and/or rain the time you're ready to make the application. The point is that you may still be able get the N applied, but there's no reason to crank up the rate very far in both cases.