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Sorghum shows potential as corn silage replacement

Courtesy of Tom Kilcer field of sterile BMR forage sorghum
STERILE SORGHUM: This field of sterile BMR forage sorghum yielded 31.6 tons an acre at 35% dry matter without lodging.
With less cultivation required, organic dairy farmers could see a huge benefit.

Can brown midrib sorghum be a good substitute for corn silage? My research, documented by Larry Chase, emeritus professor of dairy nutrition at Cornell University, shows that with proper balancing, BMR sorghum can produce the same amount of milk as corn silage.

Work at Miner Institute on BMR sorghum-sudan also documented the same milk production as corn silage, but with higher components and greater feed conversion efficiency.

BMR sorghum has numerous benefits compared to corn. Corn seed is increasingly expensive to grow. Sorghum is $100 an acre cheaper to grow for just seed cost.

Genetic rootworm resistance in corn is failing, and disease controls require expensive fungicides. Sorghum can eliminate corn rootworm when following a corn crop, is not susceptible to corn disease and also is deer-proof.

For organic farmers, corn silage requires multiple cultivations, which leaves the soil vulnerable to erosion. This cultivation, critical to the crop’s success, is done while organic haylage needs to be made. As a result, the haylage is often late, severely limiting the profit potential of the organic farm.

Plant narrow and dense

Optimum sorghum planting is in drilled, narrow rows — either 6, 7 or 8 inches — that quickly canopy to prevent erosion, shade out weeds and maximize sunlight interception in short seasons. Replicated research found an 18% higher yield compared to 30-inch rows.

Based on our work, the dense stands and rapid emergence of sorghum-sudan use a stale seedbed and can replace corn silage on organic farms without having to cultivate for weeds. Thus, more organic farms are switching to BMR sorghum-sudan as their energy forage.

My research, and that from Wisconsin, found that a one-cut management system for sorghum will double yields with little reduction in quality and can cut harvest costs in half when compared to multi-cut systems. Our work also found that most sorghum, even the Brachytic dwarf type, and especially sorghum-sudan stalks, will lodge as the grain fills, which is a major limit to farmer adoption.

Male and sterile are best

Research in New York has found that of the BMR varieties, the male-sterile variety without a seed head — either sorghum or sorghum-sudan — gave some of the highest yields and had the best standability with no maturing seed weight to bring the plant down. In paired comparisons, the male-sterile variety had higher digestibility than its seeded counterparts.

Unfortunately, with no grain we have no indicator for the optimum time to harvest male-sterile types. Sorghum breeders can’t tell farmers the optimum harvest time for the crop without seeds. This knowledge is critical to determine varietal season length and for farmers to harvest at the optimum time to support profitable milk.

Additionally, our hypothesis is that photosynthetic energy continues to build in the plant cells past heading and is not translocated to the seed sink because there is no fertile seed. So, in theory, the feed quality and milk-producing ability of the forage should continue to increase as more time is allowed for the crop to grow after heading.

We expect very little yield increase during this time — just more milk-producing ability in every ton of forage.

Field results

With the help of Brian Chittenden of Dutch Hollow Farm, and support from a Northeast Sustainable Agriculture Research and Education grant and Richardson's Seed, we established a 4-acre field in the Hudson Valley just south of Albany, N.Y., last year.

The field was planted by May 25, earlier than normal but into warmer soils with warm weather forecasted. It was the worst crop of sorghum I had grown in 40 years.

Extreme dry weather limited initial emergence and prevented most of the herbicide from being activated. An error in tillage left most of the roots in the top 2 inches of the soil, and 30% of the stand was foxtail.

The variety planted was a low-yielding, in-bred type, so that we could get enough weeks post heading before frost. Our yield from the normal parts of the field was about 12 tons of 35% dry matter silage. We’re hoping to rerun this experiment this year using a normal high-yielding hybrid that is currently growing in South America.

Fortunately, we had several blocks in the field that emerged normally and had good weed control, which allowed realistic sampling. We sampled at boot stage Aug. 10 and continued sampling weekly until a killing frost Sept. 21. Whole plants (without weeds) were chopped, inoculated and fermented for three weeks before being analyzed.

When we harvested at boot stage, the crop was 17% dry matter. As the weeks went on, the dry matter continued to increase until the last harvest was at 27% dry matter. We had a couple of late major rains, so it kept things wet.

Harvesting early means that you are hauling more water and have increased potential for leachate from your silo. We used a Chr Hansen SiloSolve MC inoculant. Across all dry matter levels, it dropped the pH to 3.65, and there was no butyric in any of the samples.

If our theory of waiting after heading to increase the forage quality proved out, it would have the immediate benefit of creating a high DM forage for more efficient harvest and fermentation.

More components

We clearly saw an increase in digestible components in the forage each week after heading. This means that instead of sending digestible carbohydrates to a seed head that most likely will not be digested, it maintains them in the plant forage cells as a fully available, slow, steady release energy source.

One example is the change in sugar that we carefully measured through wet chemistry. From boot stage through the seventh week of harvest, it increased 500% to 18.85% sugar on a dry matter basis post fermentation. Rumen-available sugar is critical to high milk protein levels.

Dumping sugar into the ration can cause low rumen pH and subclinical acidosis. The sugar contained in the sorghum is spread out through the plant cells. As rumen fungi break each cell open, there is a steady release of sugar that does not overwhelm the rumen system. This high sugar content also means that the use of an inoculant is critical for rapid silage pH drop, preserving this 100% digestible material.

In a later article, I’ll delve deeper into forage quality and the milk-producing ability of this crop.

Kilcer is a certified crop adviser in Kinderhook, N.Y.

TAGS: Dairy
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