Crop Comments: Plant sorghum after second wave of green corn seedlings

Three years ago, Canadian wildfires were ramping up. The maximum impact was felt in the northern tier of the U.S. during the second week of June 2023. Firefighters scrambled to put out blazes in Quebec, where more than 160 forest fires were roaring. These fires were fueled by high temperatures and dry conditions. Experts said we should expect more record-setting wildfires because of climate change. Failing to keep carbon in our soils has helped accelerate the issue.

Climate misbehavior was set in motion a year earlier, when all three branches of the Mississippi Basin – the Mississippi, the Ohio and the Missouri rivers – experienced widespread drought. This watershed drains 41% of the continental U.S. For all three sub-basins to be so short of water simultaneously was statistically unlikely. But that’s what happened.

The super-prevalent corn/soy “non-rotation” liberated carbon from soil into the air and shunted lost soil and nutrients toward the Gulf of Mexico. Fortunately, more and more farmers embrace sorghum, sudangrass, their hybrids and millets as forage sources for livestock.

Cheaper to grow than corn (per-pound of digestible dry matter), these hot climate summer annuals (HCSAs), with fibrous root systems, also do a much better job of retaining soil. Ongoing field research demonstrates increasingly that brown mid-rib (BMR) male sterile forage sorghum can successfully replace corn silage in cattle diets.

Trying to get a better handle on this climate misbehavior, I tapped into the wisdom of Certified Crop Advisor Tom Kilcer.

According to Kilcer, multiple replicated male sterile sorghum trials, with proper nutrient-enhancing and delayed harvest, were conducted in several states. Scientists determined that this crop can produce, at less cost, nearly the same milk as corn silage, with better components. Conventional (non-organic) dairy farms found that it is 90% cheaper (in terms of seed cost) to grow sorghum than corn silage. And that’s before factoring in all the ag chemicals needed for corn, but not sorghum.

Corn stops growing at 85º F; sorghum keeps performing up to 105º, providing more total growth out of the same season. Deer hide in sorghum, coming out to eat nearby corn. Its natural prussic acid (hydrogen cyanide) kills corn rootworms, so corn can safely be planted the year following sorghum. It can be direct-harvested with one cut, and with no grain you don’t have the extra cost of fuel for kernel processing.

Kilcer wrote that the first key to growing BMR male sterile forage sorghum is getting the right length of season. To maximize the digestible nutrients to be comparable to corn silage, it’s critical to have eight weeks of growth after head emergence before harvesting. This is the same as normally chopping corn silage eight weeks after tasseling. We’re talking eight growable weeks.

The crop does well with immediately incorporated manure with high organic matter (OM). The OM will supply nitrogen late into the season, supporting high crude protein (11% – 12% CP). A 25-ton silage crop at 35% DM will remove 336 lbs. of nitrogen (plus a critical 40 lbs. of sulfur) to support a 12% CP level. Shorting it drops protein. (Some growers counter this lower protein by adding feed-grade urea in total mixed rations.)

For successful HCSA stand establishment, soil temperature must be at least 60º – 65º, with warmer weather forecast for the next two weeks. (Sorghums and sudangrasses originated in sub-Saharan Africa.) Some farms tried to push it in cooler weather last spring, regretting the results, especially organic farms, where weeds out-competed the crop.

Almost always, the necessary warm weather comes after the first cutting hay crop harvest. If you push the season, it’s critical not to use organic practices and to use treated seed as well as necessary pesticides.

Clearly sorghum needs warm soils. Corn demands a minimum of 50º for three to four days – none of this 45º at night business. If corn doesn’t receive its necessary soil warmth, its color will be yellower than green. Most assuredly, soil temperatures will not have reached the 65º demanded by those HCSAs.

My practical recommendation for crop people growing both corn and sorghum is that when these temperature minimums are achieved, plant 10% – 15% of the intended corn acreage. Taking that color target one step further, when corn seedlings mimic the color of certain green tractors, soil temperature can be presumed warm enough to plant the rest of the corn. When that final big wave of corn seedlings boast that correct color, plant sorghum and/or the other HCSAs, which will take off rapidly enough to dodge most weed pressure.

An absolutely essential step, based on replicated research performed in multiple states, is the population planted and row width used. The old farmer’s tale is to plant it at 15 – 20 lbs. of sorghum seed/acre (which at the average seed count per pound drops 225,000 seeds/acre – less than one inch between plants on 30-inch rows). This practice, Kilcer said, is bad science. Over 40 years ago, there was extensive research on high-population corn planting – 40,000 to 50,000 per acre. Resulting crops fell over before harvest, like over-planted sorghum does. The smaller stems had a huge increase in percent rind (outside rim of the stem with high lignin), which greatly decreased forage digestibility. The same is true with sorghum.

Quoting Kilcer: “What we have found is that as we increased in-row spacing, the sorghum stalks got as big as corn stalks at the same population, and the lodging issues decreased or disappeared. Yield and digestible fiber were still maintained.”

During the year (1977-78) that my waning Extension service overlapped with Kilcer’s start as an agent, a common seed-corn planting rate was one bag for three acres (80,000 units on that acreage). With 90% “germ,” the final population is about 24,000. A standard single-cross hybrid costs about $35/bag. In the intervening almost half-century, seed-corn prices have increased almost six-fold, and most seed-corn dealers recommend a bag for two acres. That makes sorghum look pretty good, where a bag can cover six or seven acres.

by Paris Reidhead