AgriLife Research study: Harvest management can enhance sorghum silage value

 

Forage sorghum silage is an alternative to corn silage due to its drought tolerance, but management is key to making the silage valuable, according to a Texas A&M AgriLife Extension Service specialist.

 

Jourdan Bell, Ph.D., agronomist jointly appointed to both AgriLife Extension and Texas A&M AgriLife Research, Amarillo, planted 92 sorghum hybrids along with some corn for a side-by-side silage comparison in her research trials northeast of Bushland.

 

In general, if water is not limited, corn will yield better, which is why corn silage is often the silage of choice, Bell said. But, corn loses yield and quality when water is limited. If the crops are drought stressed, sorghum will “shut down” at peak water demand periods, while tasseling corn will lose quality more quickly than with sorghum.

 

“Our research has shown high-yielding, high-tonnage forage and grain sorghums can yield a high-quality silage,” she said. “And with proper harvest timing and processing of the grain, you can improve the quality of that silage.”

 

Bell said her forage sorghum trials are about more than the farmer looking at yield differences. Part of her educational message is the importance of harvest timing and how that forage is managed after it is harvested.

 

“If we can promote optimal management, we can increase the adoption of forage sorghums,” she said.

 

 

Bell and a graduate student, in a collaborative research study sponsored by the Texas Grain Sorghum Board, evaluated forage sorghum silage quality. The silage study included two harvest stages – soft-dough and hard-dough, with and without a kernel processor, and four ensiling durations: 0, 30, 60 and 120 days

 

 

“We wanted to evaluate how ensiling duration affects silage quality,” Bell said. “Ideally, producers should harvest forage sorghum at a soft-dough grain stage when the forage moisture is 65%-70% and use a kernel processor to optimize forage quality. But many challenges can delay harvest such as equipment breakdowns, precipitation and even delayed forage dry down due to the stay-green trait.

 

“Additionally, producers are generally paid by the ton, and they do not receive a premium for forage quality,” she said. “So, it may be in the best interest of the producer and the feeder to discuss a premium to compensate for reduced tonnage if an earlier harvest is desired by the end-user.”

 

Optimizing quality

The study data confirmed that silage stabilizes quicker when harvested at soft-dough, Bell said. Silage harvested at a more mature grain stage took 120 days to stabilize. She said a fermentation analysis can give producers an indication of silage quality.

 

Silage pH is a measure of the silage acidity. The pH of fresh forage sorghum is about 5.5 while the pH of ensiled sorghum is between 3.6 and 4.2.

 

“Because ensiling is a fermentation process, we want the pH of the silage to drop quickly,” Bell said. “If the drop in pH is slow, spoilage can occur as a high pH environment favors the growth of bacteria and molds. Silage pH is also related to protein breakdown in the pit. When the pH of silage is greater than 4.2, protein will break down to ammonia resulting in nitrogen and protein losses.”

 

She said by evaluating a fermentation analysis, they saw that the pH of the silage harvested at soft-dough, both with and without a kernel processor, dropped to 4.0 by 30 days. The pH of the silage harvested at hard dough was still greater than 4.5 after ensiling 30 days. The hard-dough harvested silage had a gradual decline in pH and took 120 days to reach the upper level of the ideal pH.

 

Lactic acid is another key characteristic of quality, Bell said. Because lactic acid is the primary acid of fully fermented silage, it is responsible for the final drop in pH and responsible for stabilization. The lactic acid levels of soft-dough silage quickly spiked to optimal levels, but did not reach desired levels until after 120 days of ensiling with the hard-dough silage.

 

“From an end-user standpoint, knowing the growth stage of the forage sorghum provides information on the necessary ensiling duration for forage sorghums harvested at different stages,” she said.

 

 

Another concern for some may be optimizing the starch from the forage, Bell said. In looking at starch digestion in situ, the research group confirmed harvesting sorghum at soft dough, whether cracked or whole berry, had greater than 80% of the starch utilized. Silage harvested at hard dough had closer to 60%-70% of the starch utilized and required a longer period in the pit to ensure fermentation and ideal access to the starch.