Ensiling Sorghum-Sudan Grass

Many producers have been experimenting with sorghum-sudan grass, in many cases with limited success.  Unlike corn, it has an ability to regrow if moisture and heat are sufficient, thus there is interest from producers who want a two-cut sorghum-sudan grass hay system or multiple pass grazing.  The varieties being used have not been developed specifically for Manitoba’s growing conditions, most importantly, they are not suited to the frequent wet/cool springs.  As a result, growth is often slowed, and additionally hampered by highly competitive spring weeds.

Prussic Acid

In addition to issues with accumulating nitrates, prussic acid accumulation also needs to be on the radar when harvesting sorghum-sudan grass for feed. Prussic acid levels are a result of compounds specific to sorghums and sudan grasses that can release cyanide under certain situations, primarily the same conditions that accumulate nitrates. Plants can also have more prussic acid if the soil nitrogen levels are high, and potassium and phosphorus levels are low. It can also be found in new growth (ie. Two-cut or multiple-pass grazing systems). In fact, new leaves and shoots can accumulate 2 to 25 times more prussic acid than stems (the opposite for nitrates). There are some varietal differences in prussic acid levels, however, not in varieties typically grown in Manitoba.

Regrazing new growth should not occur before the new growth is at least 24 to 30 inches tall. If a frost occurs, it is recommended to wait about 5 to 6 days for the forage to dry (and prussic acid to dissipate) before regrazing. During this time, levels of prussic acid can decrease by as much as 75%. The same could be said for the curing process when it is cut for hay. Ensiling sorghum-sudan grass crops will also lower prussic acid levels. It is recommended to simply wait one or two months before feeding to allow the prussic acid to gas off during fermentation.