You may ask: What happens if I skip a phosphorus application this year? The answer depends a lot on the starting point. What are your soil test levels? Have you built them up and been maintaining them or have you been keeping them lower in order to capture short-term gains from annual applications?
Here are some warning signs that skipping an application could result in yield losses this year:
1. You’re banding liquid at lower rates. Applying half to a third of the recommended rate in a band relies on the increased plant use efficiency of the banded nutrients to reduce rates. These rates are often below those needed to maintain soil fertility levels. Following this recommendation for many years can deplete soils of P and potassium (K). It can also limit yield unless combined with an occasional higher rate broadcast application.
2. You’ve skipped before. Soil supplies can last only so long before they need to be replenished.
3. You’ve just rented a new piece of ground. The fertilization history is probably unknown and previous management may not have been up to par. After all, the previous renter isn’t farming it anymore.
4. It’s been awhile since you’ve taken soil tests. If you can’t find the last report, it’s probably time to reassess. You don’t want to fly blindly, especially considering the costs now.
On the other hand, if you’ve been keeping up with maintenance applications and your soil tests are higher, your soil may already have all the P and K the crop needs this year — allowing you to skip. Just remember that what comes out must eventually go back in to sustain fertility.
T. Scott Murrell is northcentral director for IPNI in Indiana, U. S.