As I started writing this column the afternoon of June 17, our home’s remote-sensing thermometer registered 87º, which would turn out to be the day’s peak temperature. Right after that reading, at about 4 p.m., a phone recording from the Otsego County Office of Emergency Services stated that during the next week our area would be experiencing unusually high heat and that people should make a conscious effort to stay hydrated and avoid any possibility of sunburn.
Agronomically, that 87º mark is two degrees past the temperature that growing degree days (GDDs) cease accumulating (as far as corn is concerned).
The base for calculating GDD is 50º. A day that averages 75º is said to accumulate 25 GGDs, as far as corn is concerned. A day that averages 80º amasses 30 GDD; however, temperature above 85º doesn’t count. Basically, the temperature tally mechanism stops at that milestone (for corn).
Corn enjoys the fact that it belongs to the C-4 group of plants. Explaining that term as simply as possible, C-4 group members have structural “building blocks” consisting of four-carbon modules. Such plants are very efficient at economizing available moisture. All other plants are classified as C-3s and aren’t nearly as adept at retaining fluids (in a good sense) as C-4s; unfortunately, Palmer amaranth – a renegade virulent type of pigweed – belongs to the C-4 group.
There are other crops in the grass category (like corn) that are better adapted to hot weather than corn. They are all C-4s and are called hot climate summer annuals (HCSAs). They fall into three basic sub-groups: sorghums, sudangrasses and millets. Unlike corn – which originated in Central America – the HCSAs had their beginning much farther east. Sorghum and sudangrass developed in sub-Saharan Africa, while millets are believed to have developed in India and China.
These three sub-groups definitely developed in hotter climates that corn; most likely, this is why they keep performing as temperatures surpass corn’s 85º functional limit.
To try to come up with useful crop recommendations, well-geared to the quirkiness of summer 2024, I tapped into the wisdom of Tom Kilcer, Certified Crop Advisor and retired CCE field crops agent. To research this subject further, check out Kilcer’s monthly newsletters at advancedagsys.com. I’ll home in on the points that Kilcer stressed to me very recently.
The first of the HCSAs that Kilcer singled out was male-sterile brown mid-rib (BMR) sorghum/sudangrass hybrid. He recommends that this crop be harvested only once, i.e., not subjected to multiple cuttings; there won’t be any seed heads to make the plant top-heavy. He said that two cuttings does not increase total dry matter harvested per acre and it significantly increases wear-and tear on equipment as well as fuel consumption.
Kilcer can show that as a C-4 HCSA, this hybrid supports milk production as well as good quality corn silage does. I’ve addressed this recently, but it merits repetition: Kilcer stresses that conventional (non-organic) dairy farmers have found that it is significantly cheaper, seed cost-wise, to grow sorghum rather than corn silage. That’s before factoring in all the fungicide and other chemical sprays needed for corn silage, but not for sorghum or sorghum/sudangrass hybrids. Corn stops growing at 85º while sorghum keeps performing up to 105º.
Kilcer recommended BMR pearl millet. Even though the seed costs roughly double that of Japanese millet, the superior performance clearly justifies the additional cost. He stressed that when feeding BMR pearl millet, it is a “hotter” (higher available energy) feed; thus, additional fiber must be elsewhere in the cow’s diet to ensure proper rumen function. He also recommended brachytic dwarf sorghum, which boasts multiple leaf growth points, and thus is bushier in appearance than other sorghums. But he cautioned that brachytic dwarf sorghums can take up to two weeks to germinate.
Kilcer – along with many non-seed selling agronomists – is trying to get growers to achieve optimum sorghum and sorghum/sudangrass forage yields using as little seed as possible. He said that the old rule of thumb of planting 15 to 20 lbs. of sorghum or sorghum/sudangrass per acre has little scientific merit. He said that back in the 1980s there was a very common recommendation for farmers to plant 40,000 to 50,000 seeds of corn per acre. These high populations tended to cause much more lodging. High populations were also shown to cause the same problem with HCSAs.
With both corn and sorghum, crowding caused smaller stems, which increased the percentage of rind. (That’s the outside of the stem with high lignin.) A greater proportion of lignin lowered forage digestibility. Increasing within-row spacing – with the same population – enabled both corn and sorghum stalks to get bigger. This helped reduce lodging while protecting yield and fiber digestibility.
Kilcer explained that the 15 to 20 lbs./acre of sorghum seed meant that about 225,000 seeds were planted per acre, resulting in about one-inch spacing between seeds in a 30-inch row. Cutting the per-acre seed drop in half appears very beneficial. Planting the same number of seeds in 7.5-inch rows has been shown to increase forage yields 18% compared to what was harvested in 30-inch rows.
To further investigate the wisdom of lower sorghum/sudangrass populations, this growing season Kilcer is overseeing seed drop rates ranging from 30,000 to 150,000 per acre. He said seven inches between consecutive seedlings in a row appears optimal.
I asked him if he remembered that back in the 1970s – when he and I were both county agents – if he recalled that a common corn planter row setting was 36 inches and a target seedling population was 24,000/acre, with seven inches between plants. He recollected such, but also the fact with that wide a row spacing it took too long for sun’s rays to stop hitting bare soil.
Leave A Comment