Getting seed in, up and off to a good start
Whether the final use is for silage or grain, having a good crop of corn this coming fall means beginning with a good stand. This involves several decisions to be made this spring, including matching the corn hybrid to field conditions, seed population, planting depth, fertilization and pest control. We’ll touch on all of these, plus a couple of other topics, as we proceed.
Corn hybrid/site selection
By now, you should have most or all of your seed corn ordered. Early ordering saves you money and gives you the best chance of getting the hybrids you want in the seed size you prefer.
Research has shown that seed size itself has little influence on yield potential. However, very small seed size often requires recalibration of your corn planter units, since small seeds, particularly small rounds, often plant at a considerably higher rate than do medium and large seeds. This can be particularly true if you plant at 6 mph or more, as many farmers do. Today’s hybrids have the ability to yield well at a fairly wide range of plant populations, but planting small rounds at 6 mph or more without recalibrating your planter can result in plant populations that will challenge even the best hybrids.
If you plant brown midrib (BMR) hybrids, pay particular attention to soil type and soil fertility. BMR hybrids have become increasingly popular because of their excellent forage quality – they really put milk in the tank – but they need soils with good water-holding capacity and adequate fertility. Plant breeders have improved the yield potential of BMR hybrids, though university trials show that they still have some yield drag. Planting a BMR hybrid on low-fertility, thin soils, especially combined with midseason drought stress, can really hammer silage yields.
Midwest research years ago uncovered a surprising relationship: When the same corn hybrid was planted in a field for two years in a row, some hybrids yielded less than when they were planted following a different (genetically distinct) hybrid. This was apparently due to some form of autotoxicity. However, other corn hybrids weren’t affected; they could be planted in a field two years in a row without any negative impact. The yield difference wasn’t large, but it was there.
The corn in these trials was harvested for grain; we have no idea if the same thing would occur under silage management, but we think that any impact would be reduced. That said, it only takes a bit of planning to avoid planting a hybrid in the same field two years in a row – better safe than sorry.
The “right” population depends on the hybrid, the field and the intended use of the crop. Some hybrids don’t do well at high populations, a characteristic usually noted in the company’s seed catalog. If in doubt, consult your seed dealer.
If the field doesn’t have good water-holding capacity and often suffers during dry weather, don’t push population too high. That said, more corn is underplanted than overplanted, leaving some yield potential in the bag, so to speak.
In most cases, plant at least 32,000 kernels per acre – and on good soils, 35,000 isn’t too many. Figure on losing 10 percent of the seed to various causes. Of this 10 percent, little is due to nongerminating kernels; even though germination may be stated as 95 percent on the seed tag, actual germination is often several points higher. Improved seed handling prior to bagging, better seed treatments and more precise corn planters have combined to result in a higher percentage of corn kernels that make it “from bag to bin” (or silo).
Seed treatments applied by the seed company provide good protection against most insects and fungal diseases that attack between planting and emergence. After emergence, you have to rely on genetic resistance, genetically modified traits, natural enemies to pests and pesticides.
Prudent farmers get off their tractors several times during corn planting to check planting depth. This is particularly important for no-till planting or when any new field preparation method has been used.
The ideal planting depth depends somewhat on soil temperature and moisture conditions. Early-planted corn should be planted about 2 inches deep. If it’s planted 3 inches deep or more, the soil may be cold enough to delay germination, increasing the chances of seed rots even if the seed was treated with a fungicide. However, even with early planting into cold soil, you shouldn’t plant less than 2 inches deep.
Research has shown that corn planted more shallowly than 2 inches is more affected by early-season dry spells, and the yield impact can be significant. If you have to choose a single depth, 2 inches would be my choice until well into the planting season, and even then it would depend on soil temperature and surface moisture conditions.
You should plant corn at a depth that will allow the seeds to imbibe water and germinate quickly and uniformly. Not planting deep enough under dry conditions can result in uneven germination, a problem that’s more serious than many farmers realize. A corn plant emerging a week later than the ones around it will never catch up and will lag in development and final yield.
Use your pocketknife or a similar tool to carefully scrape away the soil covering the seed, and don’t stop when you find only one or two seeds. After you find several, making sure you haven’t disturbed them in the process, check the planting depth. Any farmer who winds up a day’s corn planting without soil on the knees of their trousers isn’t making contact in the right places.
It’s particularly important to check planting depth during no-till planting, and not just in the first field or two. Soil type and previous field activity can combine to result in very different soil conditions from field to field. An additional challenge with no-till is making sure that the packer or press wheels are covering the seed.
Clay loams are more plastic in nature, particularly during moist spring conditions, and therefore more difficult to manage for no-till. If you can see even a portion of the seed peeking out of the furrow, the chances are that it will never germinate, and at best it will be one of those yield-reducing laggards.
Corn needs phosphorus (P) early in its growth. Inadequate P availability at or soon after germination – whether due to low fertility or adverse soil conditions, including low pH and cold, wet soils – can’t be corrected by later fertilization.
P is less plant-available in cold soils, which are more common in the northeastern U.S. and with early planting, so starter P is more common in this region. One pound of P in the fertilizer band, typically 2 inches below and 2 inches to the side of the kernel, has the same effect as at least 4 pounds of broadcast P fertilizer.
Soil P levels on dairy farms are often high because of repeated manure applications. That’s why a large number of on-farm trials coordinated by Cornell University agronomists over a period of several years found that starter P was seldom needed when soil test P levels were high.
Unless manure was applied and incorporated this spring, some nitrogen (N) should be included in the starter fertilizer. The rate depends on field history – primarily manure applications – and if the field was in corn last year, but in general, 20 to 30 pounds per acre of actual N should be enough to get the corn out of the ground and to the stage of growth where it would need supplemental N.
Rely on soil analyses and perhaps tissue analyses from last year to indicate if you should include zinc and/or sulfur in the starter fertilizer. If you use a crop consultant, which I highly recommend, involve him or her in the process.
Last month’s Forages column dealt with the growing problem of Bt-resistant western corn rootworms, so we won’t dwell on this any further.
Corn hybrid and seed selection is a much more complex issue now, because not only do you have a number of genetic traits to select from, but also two or three different rates of seed treatment that can result in quite different levels of insect control.
Northern corn leaf blight has been serious in some areas. This foliar disease gets a start fairly early in the growing season and therefore has more potential for damage than a later-occurring disease such as eyespot. Hybrids differ widely in resistance to northern corn leaf blight, something to consider as you make seed selections. Some, but not all, seed catalogs include resistance ratings for this disease. If the catalog doesn’t include this information, your seed company representative may be able to provide it. Seed companies evaluate their corn hybrids for many traits that aren’t included in the catalog. It still may not be too late to change hybrids, particularly if it’s a switch within the same seed company.
Good field records have always been important, but even more so with the advent of glyphosate-resistant corn hybrids. Each year, there seems to be a field that, because of poor record-keeping or (less commonly) an applicator mistake, winds up proving how effective glyphosate is at killing non-glyphosate-resistant corn.