Crabgrass is often classified as a weed, but it also can be a useful forage crop. It makes sense to take advantage of any attractive opportunity to provide forage to cattle and other livestock, so it also makes sense to consider using, encouraging, and even planting crabgrass in certain situations on many farms in Alabama.
There are actually several species of crabgrass that can be found in Alabama, but large or hairy crabgrass (Digitaria sanguinalis) is the most common. Crabgrass is widely adapted, but does best on well-drained soils, especially sandy loam, sandy clay loam, or clay loam soils. Though crabgrass is an annual, it usually is not difficult to obtain reseeded stands year after year. Its dry matter yield is rather erratic, depending on how early a stand is obtained in spring and on factors such as fertility and rainfall, and can range from only one or two tons/acre to over five tons/acre.
The forage quality of crabgrass is typically better than that of most other summer grasses. For example, crabgrass hay is usually of higher quality than that of bermudagrass, bahiagrass, or more the most commonly planted summer annual grasses such as pearl millet or sorghum-sudan hybrids. In grazing tests with yearlings in Oklahoma, average daily gains of yearling calves on crabgrass have been as high as 1.8 pounds; by comparison, ADG's on bermudagrass or bahiagrass are typically around 1.0 pound.
The most common situation where crabgrass benefits forage programs on Alabama farms is in places in which it volunteers. If pastures or hayfields are thinned by adverse weather conditions or other stresses, crabgrass often will "fill in gaps" in perennial forage stands and thus make a significant contribution in years in which such fields would otherwise produce much lower yields.
However, planting crabgrass can also be a highly appropriate forage production strategy. Perhaps the best example is in fields in which winter annuals are planted on a prepared seedbed each autumn. The reason this works well is because the growing seasons of winter annuals and crabgrass are quite complementary, and it is relatively easy and inexpensive to establish a crabgrass stand as the following explanation indicates.
Once a good stand of crabgrass has been obtained and managed for reseeding in a given year, alternating with winter annuals planted on a prepared seedbed thereafter is a simple matter. Shallow tillage prior to planting winter annuals will incorporate crabgrass seed and usually result in an "automatic" crabgrass stand the next spring, even if no spring tillage is done.
However, to further enhance the chances of obtaining a crabgrass stand in such a situation, or to get it started earlier, a producer can simply shallowly disk the winter annual stand (about 3 inches deep) once production has declined significantly in spring (around early May), and a new crabgrass stand will normally appear. Once a crabgrass stand is present, fertilization is the primary management practice required. By late August or early September, crabgrass growth declines, which is just about the perfect time to till the field for the purpose of planting winter annuals again.
Obtaining Seed
Crabgrass seed will probably have to be special ordered, but it is usually not too difficult to find it. However, there is a great deal of genetic diversity within crabgrass, and therefore one cannot be certain what he is getting (even which crabgrass species) if he simply purchases "common" crabgrass seed.
Years of work with crabgrass by R.L. Dalrymple and others at the Noble Foundation in Ardmore, Oklahoma, culminated with release of a variety named 'Red River' in 1988. Because this variety is known to be productive with regard to forage yield, it makes sense for any producer who wants to plant crabgrass to purchase seed of this variety rather than take a chance on common crabgrass seed.
Establishment
Crabgrass should be planted on a clean, fresh seedbed after the danger of frost is past in spring. The seedbed should be firm enough at planting that when a man walks on it, his shoe print is no deeper than 1/2 inch. Seed can be drilled about 1/4 inch deep or simply broadcast over the soil surface. It may be helpful to use a cultipacker after seed have been broadcast, as this favors rapid germination and may avoid washing of seed by a heavy rain.
Good stands have been obtained with as little as 2 pounds of seed per acre, but use of 5 pounds per acre helps ensure quick cover and a thick, productive stand. The seed can be mixed with a small quantity of a low analysis starter N-P-K (nitrogen-phosphorous-potassium) fertilizer if planted promptly after the fertilizer broadcasts or flows through a drill better than crabgrass seed alone.
If adequate moisture is present, some crabgrass seed will germinate within a few days, though the stand may continue to thicken over a period of 2 months or more from additional seedling establishment resulting from slower-germinating seed. It is not unusual for a crabgrass stand to be 6 inches high and suitable for grazing within around 30 days.
Topdressing with additional N can be done after the grass has emerged and seedlings are in the early tiller stage. This should be done when the soil is dry on top. A season-long total of at least 120 pounds of N per acre in split applications (and if the crabgrass stand is established early perhaps even 3 applications and thus higher season-long rates of N during a good summer growing season) should be justifiable. Nitrogen applications after mid-August are probably not justifiable.
Management
Crabgrass germination begins when soil temperature is around 58 degrees. Though disking a field to encourage volunteer crabgrass may be most appropriate in mid-spring in a field in which it is alternated with winter annuals, it will otherwise be best to disk a field in which there is known to be adequate crabgrass seed in late February or early March. The reason is that if there is no winter annual stand to be concerned about, this will allow crabgrass to get an earlier start and thus make more total forage growth.
If it is not necessary to till a crabgrass field in late summer or early autumn in order to plant winter annuals, there will continue to be some crabgrass growth until a killing frost occurs. However, late summer/autumn production is low and the forage is lower in quality and should be utilized by animals that have relatively low nutritional requirements.
It is usually easy to get crabgrass to reseed (it commonly reseeds even when we don't want it to). All that is necessary is to allow the crabgrass to make seed at some point during summer or autumn (a stand which gets started growing in early spring will be capable of making seed as early as June or early July). This needs to be done each year after which a reseeded stand is desired.
Because crabgrass is quite tolerant of defoliation, it can be grazed or cut as low as 3 inches. If rotationally stocked, it is best to begin grazing when pastures are no more than 12 inches high, rotate animals off when they are between 3 and 6 inches high, and restock when they are 6 to 8 inches high. In Noble Foundation tests with yearlings, stocking rates have generally been 1,000 to 1,100 pounds of calf per acre and the length of the grazing season has varied from 60 to over 120 days.
Crabgrass should be cut for hay in the boot to heading stage (normally 18 to 24 inches high), which should allow at least two harvests per year. When regrowth is desired and accumulated crabgrass forage is tall, cutting height may need to be more than 3 inches because some green leaf tissue should be left to favor quick regrowth. If crabgrass is cut before it makes mature seed, one way to get enough seed for reseeding is to leave a 6-inch uncut strip between mower swaths. If crabgrass makes mature seed before being cut for hay, forage quality will be lower.
Other things being equal, the first harvest of the year will result in the best hay, sometimes containing more than 15% crude protein and 65% total digestible nutrients. Crabgrass hay normally cures more slowly than bermudagrass, but more quickly than sorghum-sudan hybrids or pearl millet. Hay of crabgrass is dark in color and consequently may not look as good as it is.
Nutritional Value
University of Arkansas researchers conducted an in-depth analysis of the nutritive value of crabgrass. A primary reason for decline in nutritive quality as a forage crop matures is the accumulation of stem material which is less digestible than leaf matter. However, with crabgrass the quality of the stem is quite high especially compared to other warm-season grasses. The amount of fiber (NDF, neutral detergent fiber) in crabgrass remained relatively constant and quite low during July and August, 55 to 62%. By comparison, some other common forages contain the following fiber concentrations: bermudagrass - 64 to 82%, bahiagrass - 70 to 78% and dallisgrass - 68 to 71%. Obviously, the crabgrass contains appreciably less fiber and in the Arkansas study this resulted in crabgrass being broken down in the rumen 44% faster than bermudagrass. The crude protein content of crabgrass ranged from 21% in the early growth and decreased to 16% in late August. The highest requirement that a beef cow would have is about 12% thus the protein content is more than adequate. In terms of forage quality, crabgrass offers a clear advantage over other warm-season perennial grasses by offering lower fiber concentration and faster digestion rates. The high quality of the stem material appears to the main factor associated with these differences.
