Have you noticed something different about the cropping patterns this fall on open ground? Acreage of sudangrass in Stanislaus and Merced Counties has gone from less than 6000 acres last year to around 18,000 acres this year. Most of the increase has come from sudangrass planted following corn silage on dairies.
Sudangrass has traditionally been planted in the late spring, after the weather has turned reliably warm in mid May. Planted at this time, it is reasonable to expect at least three cuttings of 2 to 3 or more tons of hay per acre. Popularity of sudangrass over the last 10 or 15 years has been slowly increasing as its reputation of being a poor feed is overcome by proper cutting and management. While it is tempting to allow sudangrass to head out (produce a flower stalk) in order to achieve very high yields, this results in poor quality feed. The best time to cut is in the boot stage, before there is any sign of heading. There has been a good market for sudangrass hay for export to Japan, providing expectations of the exporter are met.
The recent increase in acreage in sudangrass locally has not been due to sudangrass for hay planted in the spring but because of sudangrass being planted for silage following corn silage in August. Planted at this time, between 9 and 12 tons of silage can be grown in less than 60 days. Nearly all of this acreage is associated with dairies who use the feed for non-milking cows and young animals. Since the sudangrass is following corn, and will be followed by a crop of winter cereals, the growers are getting three crops off the same ground in one year. This is called triple cropping.
This has been an ideal year for triple cropping. A lack of rain in the spring allowed early planting of corn, and the nearly perfect temperatures this summer caused the corn crop to mature quickly. This left many growers with open ground in August, and the opportunity to grow another crop of feed. The exceptionally warm fall we have had has also been great weather for growing sudangrass, which loves hot weather and will turn sickly when the weather is cool.
Triple cropping requires a lot of fertilizer inputs in order to keep production levels high. This is actually an advantage for dairies who usually have an excess of nitrogen in the form of manure and dairy lagoon water and need a crop to put it on. The fall timing works well for them because it gives them a place to empty out the dairy lagoon in preparation for winter.
Sudangrass is very good at picking up the last bits of nitrogen in the soil and will leave the ground depleted for the next crop. Additional nitrogen in the form of manure, pond water or commercial fertilizer is often necessary to get the next crop going. However, if nitrogen fertilizer is excessive, the sudangrass will pick up more than it needs which can lead to high nitrates in the crop, causing animal health problems. Ensiling will reduce the amount of nitrate by 50 to 70% in most cases, but the silage should be checked under these conditions because it is possible to have initial nitrate levels so high that they are still too high even after ensiling.
Sudangrass varieties that are grown here are either a pure sudangrass such as Piper, or a hybrid cross between sudangrass and forage sorghum. The pure sudangrass tends to have finer stems and narrower leaves. The hybrids come in a wide variety of heights, stem fineness, leaf widths, stem sweetness, and growth habits. Some have a brown midrib, which has been associated with higher fiber digestibility. On these, the center line of the leaf is actually brown and the stems are noticeably soft and rubbery.
Among the varieties there is also a lot of variation in seed size, which explains part of the confusion as to how much seed to plant. Seeding recommendations range from 30 lbs. per acre or less to as much as 150 lbs. per acre in the Imperial Valley. Piper sudan seed is very tiny, and looks almost like large johnsongrass seeds. The sorghum-sudan crosses have round seed like sorghum of greatly varying sizes, but all of them are larger than the true sudans.
With help from Stanislaus Farm Supply and many others, I organized, a sudangrass variety and seeding rate study on Foster Farms Dairy near Hickman this past fall. In this trial, there were over 25 different varieties of sudan and sudangrass crosses. In order to compare them on an equal basis, all were planted at 1 million seeds per acre. This worked out to a range of seeding rates from 44 to 77 pounds per acre for the sudan-sorghum hybrids and would have been 25 pounds of seed per acre for Piper sudangrass.
Seeding rate influences stem diameter, which is why growers use such high seeding rates in the Imperial Valley. In that location, nearly all the sudangrass is grown for hay for export mainly to Japan, and they prefer very fine stems. According to studies conducted in the Imperial Valley, high seeding rates reduce the stem diameter only in the first cutting. It makes no difference on subsequent cuttings. At the same seeding rates, the pure sudangrasses like Piper have much smaller stem diameters than the sudan-sorghum hybrids. In the Imperial Valley study, increasing the seeding rate did not result in a significant increase in yield.
The trial conducted this fall also included a seeding rate study for several sudans, sorghum-sudan crosses and a forage sorghum. Trial results are not yet complete, but preliminary observations do show a decrease in stem diameter at higher seeding rates. Finer stems make nicer hay and facilitate wilting and drying, but the real question will be if finer stems actually improve feed quality. An In Vitro (using rumen digestive fluid) fiber digestibility analysis is planned to be run on samples from the trial to help answer that question.
November 5, 1999