Summer annual grasses are used for summer pasture, green chop, hay, silage, and winter pasture. They are often used as sources of emergency forage. In addition, residues of summer annuals make an excellent seedbed mulch for new stands of perennial grass, particularly on sands.
The summer annual grasses most often used for forage in Nebraska are sudangrass, hybrid sudangrass, sorghum-sudangrass hybrids, and forage sorghums. Foxtail millet and pearl millet are used occasionally. Each of these grasses has unique growth characteristics that require proper management for optimum production.
Some of the desirable characteristics of summer annuals are rapid growth (especially in mid-season), excellent drought resistance, and good response to fertilizer and water. Alkali soils can reduce yields considerably, but plants will tolerate a moderate amount of salinity. They are well adapted to most areas of the state and grow rapidly following planting in late May or June. They provide good growth from mid-July through August, and then moderate growth until stopped by fall frost.
Sorghum-sudangrass hybrids produce about the same amount of feed as sudangrass when used for pasture. When used for green chopped forage, yields of sorghum-sudangrass hybrids usually exceed sudangrass or forage sorghum. Forage sorghums are usually best for silage. Making sorghum-sudangrass into hay can be difficult because drying is slow.
| Yield level (Percent) |
|
|---|---|
| Sorghum-Sudangrass | 100a |
| Sudangrass | 72 |
| Hybrid Sudangrass | 81 |
aBased on ave. yield of 5.9 tons dry matter per acre.
Cattle consuming some sorghum-sudangrass hybrids sometimes gain or milk less than those consuming other summer annuals, apparently due to a lower energy content. When these hybrids are cut at immature stages, quality is higher but yields are much lower.
Forage sorghums usually yield more silage dry matter per acre than dryland corn, and will yield similarly to corn under irrigation. However, yields of TDN per acre are usually lower from forage sorghums than from corn.
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. Forage sorghums can be cut for hay, although their stems dry very slowly after cutting.
Foxtail millet does not root securely into the soil during early growth and is slow to regrow following grazing. Thus, it is not recommended for grazing except in an emergency.
Sudangrass and pearl millet produce better pasture than sorghum-sudangrass because they are usually leafier. They also provide a more uniform supply of feed for grazing and support higher daily gains or milk production. Sorghum-sudangrasses produce higher yields, but are better used to support livestock on maintenance or lower productivity levels.
Graze these summer annual grasses in a short, rotational grazing system. Subdivide fields into three or more pastures so that each pasture can be grazed down in 7 to 10 days. Stagger the date of planting each pasture by about 10 days so that grazing will begin on each pasture when growth is at the appropriate height. This rotation system allows maximum production of nutritious forage. Pastures can be irrigationd and fertilized after each grazing period if desired.
Graze sudangrass and pearl millet when they reach 15 to 20 inches in height and sorghum-sudangrass hybrids when they are 18 to 24 inches tall. Danger from prussic acid poisoning will be low when grazing is delayed until grass is this tall. Graze down rapidly to 6 inches of stubble before moving livestock to a fresh pasture, and do not graze regrowth until 18 inches of growth accumulates. If growth is more than 36 inches tall, harvest as hay, green chop, or silage since grazing cattle will trample and waste much of the growth. Regrowth will be more rapid following cutting this taller growth than if it is trampled.
| When to SEED | ||
|---|---|---|
| Field A | Field B | Field C |
| During late May or early June. | 10 days later than Field A. | 10 days later than Field B. |
| How to PASTURE | ||
| Field A | Field B | Field C |
| About July 1. After grass is 15-20" high and for 7 to 10 days. Then move livestock to Field B. | Graze for 7 to 10 days. Then move livestock to Field C. | Graze for 7 to 10 days. Then move livestock to Field A. |
Summer grazing lasts about two months. During this time each acre of these pastures can provide feed for one to six mature dairy or beef animals. Grazing management and soil fertility and moisture will determine production at any location.
Sudangrass, sorghum-sudangrass hybrids, and forage sorghum pastures are not recommended for horses because kidney ailments may develop.
Trampling and field losses will be lower during pasturing if the crop is planted in rows 20 inches wide or wider, and cattle are limited to areas that furnish only a week to 10 days supply of feed at a time. Only mineral and vitamin A supplementation should be needed when cattle are grazing immature forage during early winter. If the crop matures before frost, protein supplementation may be desirable for cows within 60 to 90 days of calving.
Field losses are less from green chopping than from grazing or haying. However, the fast rate of growth of sorghum-sudangrass results in variable amounts and quality of feed throughout the growing season. When grass is young and growing rapidly it may contain 20 percent crude protein and produce a highly succulent feed. As the crop grows taller and nears maturity the protein content may drop to 7 percent or less, and a coarse, fibrous, low quality green chop is produced.
| Stage of Maturity | TDN | Crude Protein |
|---|---|---|
| percent | ||
| Early Vegetative | 71.5 | 19.7 |
| Late Vegetative | 70.9 | 16.6 |
| Boot | 67.7 | 13.6 |
| Heading | 65.3 | 12.6 |
| Bloom | 61.5 | 11.0 |
| Dough | 58.8 | 7.8 |
Nitrates can become a problem in a green chop program under certain growing conditions. Never feed green chop that has heated in the wagon, feed bunk, or stack, or that has been held overnight. Nitrates are converted to nitrites as plants respire; nitrites are about 10 times more toxic than nitrates.
Foxtail millet should be harvested in the late boot to early bloom stage for good quality hay. Crude protein will then be about 8 to 10 percent and TDN about 55 to 60 percent. Later harvest will lower quality and cause feeding problems due to seedhead bristles.
Do not feed horses foxtail millet hay as a major component of their diet. Damage to the kidneys, liver, and bones can occur due to a glucoside called setarian.
Most summer annual grasses need to be wilted or mixed with dry feeds to make a satisfactory silage. Silage is often cut after frost to reduce moisture, especially with forage sorghums.
The moisture content should be 70 percent 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 between 70 and 75 percent moisture can be stored in trench or bunker silos. Dry feed can be added to high-moisture forage to reduce the overall moisture level.
Pearl millet and foxtail millet cannot tolerate cold, wet soils. Soils should be 65 to 70°F before seeding in June. Seedings can be made as late as July 15 and still produce a respectable hay crop if moisture is available.
Plan your seeding date to produce desirable feed when you need it. Stagger planting dates to aid rotational grazing. Seed about August 1 for winter pasture. Remember: little usable forage is available until about 6 weeks after planting.
For good stands, plant high germinating seed that has been treated with a fungicide.
Use soil tests to determine phosphorus and other fertilizer needs. Apply 40 to 80 pounds of N per acre around seeding time. Where moisture is adequate, higher rates may be justified. Split applications of nitrogen will provide a better distribution of grass growth and lessen the nitrate poisoning potential, especially when the total amount of N to be applied exceeds 60 pounds per acre.
Avoid feeding hungry animals young succulent feed of these grasses. Allow plants to reach heights of 15 inches for sudangrass and 18 inches for sorghum-sudangrass crosses before grazing to dilute the concentration of prussic acid in the plant. Do not graze forage sorghums unless they are several feet tall. Give animals a full feed of hay before first turning them onto pasture, and always have plenty of clean, fresh water available. Free choice salt and mineral with added sulfur will help minimize the toxin's effect.
Pearl millet and foxtail millet have not caused prussic acid poisoning and prussic acid has not been found in the plants.