Luxury Feeding the Corn Grain

As we discussed last time, at the R5 growth stage, corn is dying to fill the developed kernels with photosynthate by remobilizing nutrients from leaves and stalk into the ear.  If the plant already has reduced levels of nitrogen due to stress or poor management, excessive cannibalization as senescence will occur.

But what happens if there's plenty of nitrogen during the R5 growth stage?  Will that make more grain yield, higher protein, both, or neither?

Under High N Management

Under high yield management scenarios, nitrogen is not usually something that is limiting; in fact, growers may be tempted to apply more nitrogen as insurance.  But what happens if all goes well during the season?  What we get some moist soil conditions that contribute highly to mineralization?  Or the plants' roots tap into a layer of trapped nitrate due to a restrictive layer or clay pan?  The plant is eating at the buffet and there's a steady line of dishes coming from the kitchen.

Under high nitrogen conditions at grain-fill, corn grain can be a "luxury feeder" of nitrogen; that is, if the nitrogen is there, it will attempt to stack it away and convert it into protein in the grain.  It likely will not generate any higher yields, but it will certainly fill out what is there.

Hybrid Variation

Some hybrids will vary in their grain nitrogen concentration.  Generally, older genetic lines tend to produce higher protein (nitrogen is the main component of protein).  Modern corn breeding has exchanged grain protein for yield in most cases.  Today's typical nitrogen concentration in corn grain is 1.15-1.20% on a 0% dry matter basis.  Older genetics could range up to 1.33-1.36%.  Studies have shown a range from 0.7 to 1.7% but generally land at around 1.2%. Multiplying this by the crude protein factor of 6.25 this provides a general crude protein range of 7.2-7.5% for modern genetics.

Corn grown under high nitrogen availability will exhibit higher grain nitrogen concentration, often without any accompanying increase in yield.  Unless one is being paid a premium for high protein corn, the extra cost of nitrogen to achieve this is not worth the effort.

How Efficient is Remobilization?

Remobilization efficiency can also affect corn grain nitrogen content.  A hybrid that has efficient remobilization ability may allow the plant to shift more nitrogen to the kernels, but it has an inverse relationship with the stay-green trait.  Stay-green as a trait describes the corn plant's ability to continue to capture photosynthetic energy longer.  A highly stay-green hybrid is often less efficient in remobilizing nitrogen; it takes longer to pull nutrients from the leaves and stalks than a highly efficient one and will likely rely on late season nitrogen uptake from the soil.  This bit of knowledge may be useful for late-season nitrogen management on select hybrids.

Again, modern breeding has leaned more to higher stay-green traits with accompanying lower remobilization efficiency to capture later-season photosynthetic activity and drive yield through kernel mass.  This may also mean that at physiological maturity (R6 or black layer), the remaining stover is likely to have more nitrogen (as protein) and will either return to the soil or be useful as livestock fodder.

Summary

Luxury grain nitrogen concentration in today's commodity world is not an ideal situation.  Protein can be obtained from other sources for feeding livestock at lower costs than it would by applying excessive nitrogen, not to mention the downstream environmental effects.  Grain nitrogen concentration can be affected by hybrid traits, in particular, the genetics' ability to remobilize nitrogen from leaves and stalk to the grain vs any stay-green capacity.  The hybrids that express more stay-green could be candidates for later-season nitrogen management, if natural mineralization from the soil doesn't provide enough. 

Letting your corn grain become a luxury feeder is an expensive situation.  Ensuring enough nitrogen is available for your genetics to both develop and fill out kernels allows for the best balance of yield vs input costs.