The theory that some fields might run out of nitrogen because of extra loss during early rains is now more than a theory. It's fact. A field that Indiana Prairie Farmer watches closely, the Crop Watch '13 field, is showing signs of nitrogen deficiency in a good part of the field. Ten days ago it was the bottom three or four leaves that were showing traditional symptoms. Now it is leaves all the way up to the ear leaf – or above in a few cases.
Classic symptoms include yellowing down the mid-rib that eventually covers the entire leaf. It takes away from the leaf's ability to produce more sugars for the plant through photosynthesis.
Plants that run short on N cope by aborting some young kernels to save more mature kernels. Tip kernels are fertilized last. Two weeks ago in the Crop Watch '13 field it appeared those kernels were fertilized and 40 kernels per row would be common. The kernels fertilized, but nearly every ear checked aborted them. Now the kernel count averages more like 32 kernels per row, with an inch and a half of bare cob at the end. That's a lot of lost yield potential when 20% of your kernels are sacrificed to help fill the rest of the ear.
You want to know if your field is short on N so you can reassess your nitrogen system for next year, experts say. The stress may also cause it to fall prey to stalk rots earlier in the fall. You may have to adjust your harvest schedule or harvest at higher moisture content if stalk rot becomes an issue in stressed fields, no matter what the cause.