Under the auspices of the Cornell Departments of Animal Science and Agronomy, the results of a feeding management study were released in 2023. That study’s purpose was to determine how well brown mid-rib (BMR) forage sorghum could substitute for corn silage in supporting 85 lbs. milk/day production level in large frame dairy cows.
The corn silage-based regimen contained 20 lbs. corn silage dry matter (DM), 13.5 lbs. alfalfa silage DM, 5.8 lbs. shell corn DM and 3.2 lbs. Soy Plus DM. The BMR sorghum-based regimen contained 18.8 lbs. sorghum forage DM, 15 lbs. alfalfa silage DM, 6.9 lbs. shell corn DM and 2.4 lbs. Soy Plus DM. With protein in both silages being fairly soluble, using a heat-treated protein (like Soy Plus, with lowered protein solubility) helps rein in excess rumen non-protein nitrogen (N).
Both sorghum and sudangrass originated in sub-Saharan Africa, an area referred to as the Sahel. Both crops belong to genus Sorghum and are amazingly adept at surviving meager precipitation while tolerating high temperatures.
Certified Crop Advisor Tom Kilcer, a retired career field crops Extension agent, pointed out dramatic research findings – namely, that strategic use of manure provided enough N to both corn- and sorghum-based roughage programs to elevate whole plant forage protein levels to 11%. Compared to the corn silage-based program, the sorghum-based feeding program needed 1.1 lbs. more shell corn but required 0.8 lbs. less Soy Plus. On a 100-cow dairy, that net savings annually could be in the $3,000 – $4,000 range.
Regarding best-possible N utilization, Kilcer commented on optimized manure management: “Manure may be a superior source due to the gradual release of organic matter N throughout summer. Any manure application needs to be incorporated within an hour of spreading to capture the ammonia N. This is why more farms are adding manure injection as a standard economic and environmental practice in their operation.”
To compare sorghum and corn for dairy cattle forages, he stressed the importance of ensiling both feeds at the correct stage of maturity. Eight weeks is the magic number: for sorghum, harvest that amount of time after heads begin to form. For corn, ensile eight weeks after tasseling.
Time management with sorghum culture entails more juggling than is the case with corn. Quoting Kilcer again: “In northern areas, you are potentially squeezed between the time for heading and the soil temperature for planting. (In that respect) sorghum is not corn silage. It is critical that the soil temperature be above 60º F (preferably above 65º) with the forecast for warmer temperatures the week after planting. Don’t make the mistake I made of planting into soil that was 72º, but three days after planting got a 40º rain that killed the entire research project. Check the longer-term forecast.”
I learned the hard way a lesson similar to what he described when, about 18 years ago, I advised the ag program at the local vocational center. Impatient to get a sorghum/sudangrass (SS) hybrid planted, I waited until corn planted by neighbors emerged, then planted this hot climate summer annual. Knowing that corn could germinate at 50º, I figured that when the corn was up enough to form light green rows, it would be good time to plant SS.
The SS emerged, but took a long time to get moving, hindered by what I diagnosed as eyespot. This disease, caused by the fungus Kabatiella zeae, is common in the Northeast. This problem is much more common on corn, but apparently my SS caught the same infection.
Eyespot is favored by cool wet weather. Its spores are spread long distance by wind and locally by rain splashing from crop debris in soil onto host plants. (Interestingly, that year was also a growing season with rampant tomato blight.)
For planting sorghum (or SS), Kilcer strongly stressed that drilling in narrow rows or 15-inch rows is far superior to planting in 30-inch corn rows. His research found sorghum yielded 18% more when drilled than when planted in corn row width. (Narrower rows intercept more solar radiation in early crop development than wider rows do.) More uniform spacing increases stalk size, decreasing lodging potential. Even without a heavy fertile seed head on male sterile sorghum, too high a population for the row space increases lodging.
If a grower insists on 30-inch row spacing, experts recommend a maximum of 4 lbs. of seed/acre. For 15-inch rows, they recommend 5 – 6 lbs. of seed/acre; and if drilled, 6 – 7 lbs. of seed/acre. We need to be talking in terms of the number of seeds/acre (just like we do with corn), as sorghums range from 12,500 – 17,000 seeds/lb.
Drilled into good soils with good fertility, we want 100,000 to 110,000 seeds/acre. Planting at higher populations likely causes lodging at harvest. We don’t do that with corn – they advise not to do it with forage sorghum!
Growers should check older drills when planting these low populations, since they may be planting sorghum flour instead of seeds. At the low seed rate, the mechanism is smaller than the seed size, and it will grind the seed and nothing will grow. If this happens, growers should set the drill at double the desired population, then plug every other hole to increase row spacing. Not ideal, but better than planting sorghum flour.
Doubling the theoretical seed drop/acre while plugging every other hole in the drill works. That’s what we had to do years back at the vocational school. We wanted to plant a two-acre piece with tyfon forage turnips, using an antiquated Van Brunt grain drill. The recommended seeding rate was 3 lbs./acre. There was no way we could get seed drop that low with 7-inch rows. Plugging every other row produced successful 14-inch rows.
The school’s beefers enjoyed the foliage during grazing season. Deer dug through the snow for turnip treats all winter; teeth marks were quite visible on the gnawed purple tubers.
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