By Kay Ledbetter
Ongoing Texas A&M AgriLife Extension Service sorghum silage trials have revealed forage type and variety are key considerations to optimizing both quantity and quality, according to two specialists.
Dr. Jourdan Bell, AgriLife Extension agronomist in Amarillo, said the 2014 trials in Potter County under center pivot irrigation evaluated 90 forage sorghum silage varieties for optimal yield and quality.
Bell said because silage is in high demand by both feedyards and dairies in the High Plains, she and Dr. Ted McCollum, AgriLife Extension beef cattle specialist of Amarillo, are taking a closer look at what makes a difference in production outcomes, especially on sorghum silage.
“In many areas with declining well capacities, sorghum silages are a great alternative to corn silage,” Bell said. “Producers can achieve very good sorghum silage yields with about half the irrigation water requirement of corn silages.”
But, she said, not all sorghum silage varieties are created alike. There is great variability in yield and quality between varieties, which is why the AgriLife Extension variety trials are used by many producers as they make their variety selections.
“Variety selection is really key to achieving optimum yield and quality,” she said. “It is important to evaluate the different sorghums used for forage and silage production. When we discuss types, there are forage sorghums, sudangrasses and sorghum-sudangrasses.”
In these different types, Bell explained, there are normal or conventional varieties, brown midrib varieties that have decreased lignin and increased digestibility, and several different maturity classes, including photoperiod-sensitive varieties.
The initiation of reproduction by the photoperiod-sensitive varieties is regulated by day length, McCollum said. Reproductive activity will not begin until day length is less than 12.3 to 12.5 hours. In the High Plains, this is about mid-September. As a result, these varieties will not flower until mid-October, if weather permits.
Bell said the 2014 trials included 44 non-brown midrib varieties and 46 brown midrib varieties. Of the entries, 15 were photoperiod sensitive. She said varietal selection showed up during the trials as the key to achieving optimum yield and quality.
“We saw a wide range in yields among the varieties,” she said. “Our maximum yield was 39.8 tons per acre at 65 percent moisture, while the lowest yielding variety was 11.3 tons per acre at 65 percent moisture. The trial average was 21.7 tons per acre at 65 percent moisture. We had some very good yielding varieties.”
However, Bell said, 2014 growing conditions significantly affected yields. While 8.5 inches of irrigation was applied, the plots received 9.2 inches of in-season precipitation.
“In addition to very timely in-season precipitation that greatly enhanced crop production, we received 5.3 inches of precipitation in May and June prior to planting, which provided very good stored soil moisture,” she said.
Bell said there were also significant differences in quality between varieties.
“We evaluated crude protein, acid detergent fiber, neutral detergent fiber, lignin, starch, neutral detergent fiber digestibility and relative feed quality,” she said. “In general, the brown midrib varieties had the greatest digestibility and crude protein values, while the photoperiod-sensitive varieties tended to be lower quality and the others in between.”
Bell said because the photoperiod-sensitive varieties remain in the vegetative stage of development longer, average yields were greatest; however, lignin was greater and digestibility was lower, which is reflected in lower relative feed quality scores.
McCollum said in the 2014 trials, as in previous years, there was a great deal of overlap in quality among these different genetic types, “so comparing actual trial data for specific varieties is a better selection approach than simply using genetic type.”
“Selection of a silage variety should first consider where the silage will be placed in the nutritional management program of the end user,” he said. “Some production systems need higher feed quality and yield may be a secondary consideration, while other systems may be less focused on feed quality and yield may be a greater consideration.
“One variety or type does not necessarily fit all, especially when we reframe the thought process and include the water needs and irrigation capabilities in the discussion rather than just focusing on the end use of the silage,” McCollum said. “The diverse types and varieties give a producer and an end user the capability of fitting a variety to their capabilities and needs.”
Harvest timing is also very important with regards to silage quality, Bell said. The ideal harvest time optimizes both quantity and quality of the forage, but with silage, “we also must consider harvest moisture, which affects the packing of the silage and silage quality.”
In this trial, all varieties were harvested at or near the soft dough stage.
“Harvest timing is critical if an end user is relying on grain production in the silage crop,” McCollum said. “If harvest is delayed beyond soft dough, digestibility of the starch in the sorghum berries declines severely. It is best to err on the early side of harvest rather than the late side.”
Complete results of the forage trials will be available at http://varietytesting.tamu.edu .