In the April 2023 issue of his monthly Crop Soil News (advancedagsys.com), Certified Crop Advisor Tom Kilcer tallied field research conducted on New York dairy farms in 2020 and 2022. The purpose of this study was to determine how well brown-midrib (BMR) forage sorghum could substitute for corn silage in supporting 85 lb. 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 its lowered protein solubility) is a good idea in order to rein in any excess rumen non-protein nitrogen.
Kilcer pointed out 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, he showed that the net savings annually was in the $3,000 – $4,000 range.
With respect to best-possible N utilization, he made the following comment on optimized manure management: “Manure may be a superior source due to the gradual release of organic matter throughout the summer. Any manure application needs to be incorporated within an hour of spreading to capture the ammonia nitrogen. This is why more farms are adding manure injection as a standard economic and environmental practice in their operation.”
To make the comparison of 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 can be more of a juggling act than it is 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 later after planting got a 40º rain that killed the entire research project. Check the longer-term forecast.”
I had to learn the hard way a lesson similar to what he described when over a decade 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 neighboring farmers had emerged, then planted this hot climate summer annual. Knowing that corn could germinate at 50º, I figured that when the neighbor’s corn was up enough to form light green rows, this would be an okay time to plant the 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 and can be found across most of the Northeast. This problem is much more common on corn. But apparently my SS managed to run aground in similar fashion. Eyespot is favored by cool wet weather. K. zeae spores are spread long distance by wind and locally by rain splashing from crop debris in soil onto host plants.
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 is the case with wider rows.) The more uniform spacing increases stalk size and decreases lodging potential. Even without a heavy fertile seed head on male sterile sorghum, too high a population for the row space will increase lodging.
Kilcer explained, “If you insist on 30-inch row spacing, then we suggest a maximum of 4 lbs. of seed/acre; 15-inch rows, 5 – 6 lbs. of seed/acre; and drilled, 6 – 7 lbs. of seed. Actually, 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 to 17,000 seeds/lb. 65,000 (seeds/acre) is our population for 30-inch rows. Drilled into good soils with good fertility we want 100,000 to 110,000. Don’t let anyone convince you to plant higher population or it will be lodged when you come to harvest. We don’t do that with corn, don’t do it with forage sorghum!”
He also advised growers to check older drills when planting these low populations, since they may be planting sorghum flour instead of seeds. If at the low seed rate, the mechanism is smaller than the seed size, it will grind the seed and nothing will grow. If this happens, growers should set the drill at double the desired population and then plug every other hole to increase the row spacing. This is not ideal, but it’s better than planting sorghum flour.
The idea of 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 mentioned earlier. We wanted to plant a two-acre piece with tyfon forage turnips using an antiquated Van Brunt grain drill. Recommended seeding rate was 3 lbs./acre. There was no way we could tone down seed drop that low with 7-inch rows. Plugging every other row made successful 14-inch rows attainable. The school’s beefers enjoyed the foliage during grazing season. Deer dug through the snow for turnip treats all winter.
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