Forage sorghum is a good crop to use in rotation to break the insect and disease cycles that can develop in continuous corn.
For example, corn rootworm larvae cannot survive on sorghum roots, so sorghum after corn works well. Corn after sorghum can sometimes still be a problem because rootworm adults can lay eggs in sorghum, especially if sorghum is flowering after corn silking. Scout for this situation before going back to corn.
When adding sorghum to your crop rotation, try these recommendations:
Herbicide Choices. Sudangrass, forage sorghum, and sorghum-sudan hybrids will tolerate moderate levels of atrazine. Safened seed is required if using Dual or Bicep-like herbicides containing s-metolachlor. A list of herbicides labeled for use in sorghum in Nebraska is available in the latest edition of the UNL Guide to Weed Management. Keep in mind there are fewer herbicides labeled for use in forage sorghum compared to corn on pre- and post-application strategies.
Seeding Rate. Use 6-12 lb per acre for forage sorghum. Use the lower rates in dry areas and higher rates in humid and irrigated areas. Higher seeding rates will help produce finer stems, which often are desirable for pasture and hay. The use of 15-inch rows may help standability because stems may get thicker when plant-to-plant competition is reduced.
Nitrogen. Recommended nitrogen rates are available in the sorghum chapter of the UNL Extension guide, Nutrient Mangement for Agronomic Crops in Nebraska. Fertilize according to your yield goal which is also tied to moisture in the profile at seeding time. It is important to check soil for residual nitrogen before fertilizing to further fine-tune nitrogen rate.
Seeding Timing. Soils should be above 60°F when sudangrass and sorghum are planted. Seedings made in late May and early June usually give good results in Nebraska. For southeast Nebraska and southern tier counties the date can be pushed up a couple weeks; however, planting the first week of May can be very risky. May 15 plantings are generally OK if the seed is fungicide-treated.
No-Till Planting. No-till planting techniques can save water, increase forage yield on rainfed land, save labor, be beneficial to soil health and provide residue cover from the previous crop to protect the soil surface and influence soil temperatures in the summer to the benefit of microbial activity. Make sure your drill or planter has enough weight and down pressure to cut and handle the residue and get the seed to the proper seeding depth of 1 -1 1/2 inches. To avoid sidewall compaction, do not apply more pressure to closing wheels if soil is on the “tacky” side at planting.
Fall Cover Crop. There may be opportunities for planting a fall-seeded cover crop or cereal rye for spring grazing or a cereal rye hay crop or cereal rye green chop cut at early heading before planting forage sorghum. You have to be on top of the chopping timeframe as rye can jump up tall in a hurry and go down and/or dry out the 2-foot profile. Be aware of your cover crop moisture use.
Feed Value of Forage Sorghum for Silage. For silage choose forage sorghums, especially hybrids with high grain production. They can’t be beat for tonnage or for feed value. As silage, forage sorghums usually yield more dry matter per acre than dryland corn, and will yield similarly to corn under irrigation. However, yields of TDN (total digestible nutrients) per acre are usually lower from forage sorghums than from corn. Generally, forage sorghum silage has 75% to 85% of the energy value of corn silage per unit of dry matter, while other summer annual grasses have 60% to 80% percent of the value of corn silage.
Brown Mid Rib Trait or BMR. Use sorghum with BMR for growing calves or any cattle with higher nutrient demands. Newer cultivars have overcome most, but not all, increased lodging risk. Producers need to work with a reputable seed dealer. Use a good forage sorghum grain producer who breeds for silage.
Cautions (After Cutting the Forage Sorghum for Silage). Grazing of forage sorghums is not recommended. They usually contain much higher levels of prussic acid than other summer annual grasses and can be dangerous to graze even when plants are completely headed, especially when young shoots are present. Grazing regrowth or young plants before a killing freeze after silage harvest would be a very high risk or dangerous situation for cattle.
Forage Sorghum Silage Tips. Forage sorghums are usually tall growing and mature late in the growing season. Often called “cane,” forage sorghums have sweet, juicy stems. Many have relatively small grain heads. Silage is often cut soon after frost to reduce moisture, especially with forage sorghums. Cutting short will maximize yield from that harvest. Taller stubble (8 inches) can hasten drying, reduce the risk of nitrate poisoning, and encourage regrowth.
The moisture content should be 70% or less for good preservation in upright silos. Wilting high moisture forage can be difficult because the crop dries slowly and regrows rapidly when soil moisture is adequate. Silage at 70-75% moisture can be stored in trench or bunker silos. Dry feed can be added to high-moisture forage to reduce the overall moisture level. If you are doing this practice of mixing, mix well when trying to adjust moisture with another feedstuff. Silage inoculants can pay off especially well when moisture is in upper range.
Pricing Forage Sorghum. We suggest pricing sorghum silages in relation to corn silage of the same moisture content. Forage sorghums with fairly high grain yield in relation to forage (sorgo types) usually have 80%-90% of the value of corn silage per unit of dry matter.