Why It’s Important to Understand Forage Problems

It’s probably too late to do anything about any problems you may find with your forage, but knowing what happened – and why – is essential in trying to prevent the same things from happening again.

It’s probably too late to do anything about any problems you may find with your forage, but knowing what happened – and why – is essential in trying to prevent the same things from happening again. To quote Albert Einstein, insanity is doing the same thing over and over again and expecting different results.

Some readers may wonder why corn is mentioned in an article with “forage” in the title. I consider corn to be two crops, each with different characteristics: The kernels are a high-quality grain while the rest of the plant (the stover) is a modest quality warm-season grass. When the corn plant is harvested for grain the remaining plant is low in quality, similar to a forage grass harvested well after heading. Occasionally corn stover is baled and fed to wintering beef cows or, where there’s a serious shortage of quality forages, fed in modest quantities to dairy cattle. Several years ago I was on a crop consulting job in the Texas Panhandle during a severe drought. On some of the dairies corn stover was one of the major forages in the ration, with huge stacks of large square bales waiting to be fed. When fed to lactating dairy cows, corn stover must be supplemented with grain or higher-quality feedstuffs.

The quality of the corn plant as a forage is determined by the relative proportions of grain and stover. The higher the grain content, the higher the digestibility of the entire plant. That’s because corn grain doesn’t contain much fiber and only about 1 percent lignin, which is indigestible. I seldom include discussions about grain corn in these columns – national farm publications are chock-full of articles about this crop – but I often discuss corn silage because it’s a true forage crop. A dictionary definition of forage is “plant material that livestock graze or that is cut and fed to them.” Corn harvested for whole-plant silage perfectly fits that definition.

Corn emergence

The combination of improved seed corn production practices and better planting equipment has resulted in a slightly higher germination rate and plant population compared with the corn we planted a generation or more ago. Seed treatments (typically a combination of an insecticide and one or more fungicides) are now applied by the seed company instead of by the farmer. Not only is this safer for the farmer but there’s better adhesion of the treatment to the seed, increasing the percentage of kernels that survive to produce a plant. This, combined with higher germination rates, has resulted in a change in the recommended overplanting rate for seed corn. We used to recommend overplanting by 15 percent, so if you wanted 30,000 plants per acre at harvest you’d need to plant almost 35,000 seeds. Now, some seed company agronomists recommend overplanting by only 5 percent when field conditions are good to excellent, and by 10 percent with very early planting or under cloddy soil conditions. This means having to buy 5 percent to 10 percent less seed corn. It’s worth paying attention when a seed company recommends reducing the amount of seed that farmers would need to buy.

If you have a poor stand of corn it’s almost never because of a bad lot of seed. The exception would be corn that’s been stored on the farm for at least a year, especially if it’s been stored in a shed that gets hot during the summer. Heat is the enemy of farm-stored seeds. Unless storage conditions have been poor, seldom is year-old seed lower enough in germination to affect planting rate, but any seed older than that should be germination tested, either on-farm or by sending a sample to an agricultural testing laboratory.

Germination tests are inexpensive, well worth doing if there’s any question about viability: Test, don’t guess! Many years ago at Miner Institute we “inherited” a few bags of seed corn that were several years old when we assumed management of the dairy operation from Cornell University. Before planting it we had the seed tested and were pleased – and a bit surprised – when the germination was about 95 percent. The corn grew just fine in the field.

Planting depth

Two factors resulting in poor emergence are corn that’s planted either too shallow or too deep. A planting depth of 2 inches is ideal for most situations, but with very early planting into cold soils, planting depth can be reduced to 1-3/4 inches. This leaves a small margin for error since corn planted 1-1/2 inches deep should still germinate OK. Problems start to occur when planting depth is reduced to 1 inch, usually unintentionally. Seedbeds that are loose and fluffy – often the result of too much spring tillage – can settle by a 1/2 inch or so following a heavy rain, thus decreasing the planting depth. When the corn kernel is 1 inch or shallower, the nodal roots will be barely below the soil surface. Several problems can result from shallow planting including root damage from some preemergence herbicides, which is why it’s often called “rootless corn syndrome.” On the other end of the planting depth spectrum, corn can be planted to a 3-inch depth after the soil has warmed with little negative impact on emergence. However, with early planting – prior to mid-May in much of FARMING magazine’s area of coverage – planting corn too deep can result in delayed germination because of cold temperatures at that depth, leaving the kernels more susceptible to seed rots.

If faced with a field of corn with a poor stand, carefully dig up some emerged plants to determine how deep the corn was planted. Try to find some kernels that didn’t germinate to determine the condition of the kernel. Do this when the healthy plants are no more than about 6 inches tall. If you don’t find a kernel is it because something ate it? Seed corn maggots are a potential cause. It may also be because some of the seed wasn’t planted. It happens, though much less frequently with modern corn planters. It’s important to diagnose the reason for a thin, uneven stand of corn: Don’t hesitate to ask for help from your Extension educator or crop consultant.

Legume-grass seeding problems

As with corn, a major source of failures and inadequate stands in legume and grass seedings also relates to planting depth, either too shallow or too deep. Planting small seeds such as alfalfa and forage grasses too deep is more commonly the cause of poor stands. Although the recommendation varies with soil type, soil moisture and time of seeding, most legume and grass seeds should be planted no more than 3/8-inch deep. A good rule of thumb is that 5 to 10 percent of the seeds should be visible on the soil surface after seeding. By the time you notice problems with a seeding, however, birds and insects may have carried off any seeds that remained on the soil surface.

Herbicide damage is another potential source of injury to seedlings. This can be due to herbicide residues from the previous crop – often corn – or postemergence herbicides applied when the forages were in the seedling stage. If necessary, check with your state regulatory authorities for the herbicides that are approved for the species you’re planting. (With the exception of clear alfalfa the list will probably be short.)

Not everything is known about how the various forage grass species react to the labeled herbicides, so proceed with caution. Perhaps the most common herbicide toxicity is from atrazine, though we don’t see this nearly as often now that atrazine has to a large extent been replaced by herbicides with a shorter soil residual. Atrazine toxicity in alfalfa appears as a whitening or chlorosis of the outer margins of the leaves, followed in severe cases by the death of the plant.

Alfalfa plants produce toxins that can reduce the germination and growth of alfalfa seedlings – this is called autoxicity. These toxins are water-soluble and are concentrated in the alfalfa leaves. How long the alfalfa was growing in the field prior to seeding as well as the amount of plant debris both have impacts on autotoxicity. Heavy soil types (clay loams vs. sandy loams) are more at risk for autotoxicity because the toxins don’t leach through the soil profile nearly as fast.

Destroying an old alfalfa sod in the fall either by tillage or (particularly in no-till systems) with herbicides and seeding the following spring may not allow enough time for the toxins to dissipate. Research has found substantially poorer seedlings when alfalfa is seeded into a recent alfalfa stand compared to seeding following a different species such as corn. Alfalfa autotoxicity is usually less of a factor with conventional tillage than with no-till.

One difference between stand problems with corn vs. alfalfa is the impact that a less-than-ideal stand has on yield. Poor stands of corn almost always result in lower yields, but with alfalfa it depends on whether the problem is general across the field or in patches. Recommended seeding rates of alfalfa result in a lot more seeds per square foot than are needed for good yields. I’ve seen farmers make a big mistake in their grain drill or forage seeder settings and wind up with about half as much seed per acre as they intended. But because the population was uniform across the field, and because in most cases field conditions were very good – a fine, firm seedbed – they wound up with a perfectly adequate stand. Not that this is recommended since it was due to the combination of skill (a good seedbed) and good luck (favorable weather).