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Summer annual forages help close gaps

April 28, 2014

By Dr. Dirk Philipp, Department of Animal Science, University of Arkansas—Fayetteville


Good forage management involves keeping forage supply matched up with animal needs during that time. Summer annual forages provide hay and pasturing at times when cool-season forages such as tall fescue cease growth during the hot summer months.

We have been working with pearl millet, sorghum sudan, and teff grass for some years now, and all of them have advantages and disadvantages. All of them require relatively warm soil and air temperatures for establishment and a fair amount of soil preparation to grow them successfully and achieve maximum yields. Some producers have had success by drilling summer annual forages into dormant tall fescue, but we were unable to see good results by trying this on our research farm. While there is merit in pursuing a no-till strategy, it also comes with disadvantages. Among these are seeding rates that have to be increased, delayed planting time as fescue dormancy may not occur until July, and likely lower yields compared with tillage-based establishment.

Establishment success of summer annuals can be vastly improved by preparing a firm, well-settled seedbed using a disk plow followed by culti-packing or rolling. As always, having a soil test report on hand is mandatory for good forage management and the report for the selected field should not be older than 1 to 2 years. Keeping the pH in the optimum range between 6.5 to 7.0 is helpful too because that will save a lot of headaches later on if the field is rotated to other crops such as legumes that are sensitive to soil acidity.

Soghum-sudan, pearl millet, and teff showed very different amounts of dry matter production during a study we conducted last year at the Fayetteville location. Sorghum-sudan (~7,500 lb/acre) out-yielded pearl millet (~5,200 lb/acre) and teff (~3,100 lb/acre) by far. But the entire story tells us much more than just the yield. We harvested twice, on July 31 and September 5, after having planted all grasses around June 15. While the amount of regrowth for sorghum-sudan was similar to the first harvest, both pearl millet and teff accumulated twice as much biomass between July 31 and Sep 5 as they did between the planting date and the first harvest. All grasses were harvested at the recommended heights of 4 inches for teff and 6 inches for the other grasses. There was little rain between the planting date and the first harvest end of July, so it is possible that the increased biomass accumulation was primarily caused by increased precipitation. This also means that in years with average amounts of rainfall during spring, it is wise to plant these grasses as early as possible, provided that soil temperature is at least 55 to 60 degrees F. Because these grasses are annuals and grow rapidly to reach the reproductive phase quickly, the regrowth potential is high and cutting or grazing cycles should be kept as tight as possible. Another benefit of harvesting on schedule is weed control, especially with teff. The harvested area was virtually weed-free, while another strip we did not harvest was completely overrun with weeds, among them pigweed and yellow nutsedge. Weed control in sorghum-sudan and pearl millet is usually not a big problem as these forage crops shade the soil enough to prevent major weed development.

There is obviously the danger of nitrate accumulation, especially in pearl millet and sorghum-sudan, and in addition prussic acid accumulation in the latter. With careful management and applying simple rules, such as leaving at least 6-inch stubble after harvest or grazing, the danger can be minimized. These summer annuals can also be part of rotations followed or preceded by winter annual forages such as legumes. In that case, some of the synthetic nitrogen fertilizer needed may be offset by the added legume biomass during the tillage process.

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