BMR Sorghum-Sudan (SxS) has been around for approximately 20 years. During this time, we began seeing its value as a quality forage for high-producing dairy cows and began moving it farther north from its typical homes of Texas and Kansas. One thing became completely clear, when especially corn, but any crop followed SxS, it seemed thenext crop did better! Could it just be the effects of ordinary crop rotation or is something extra going on? This letter will delve into this question.
Obviously, anytime we have a crop rotation, better things happen from a soil quality standpoint over corn after corn after corn. However, continually, we see and hear that the corn after a SxS rotation in the previous year is the “best corn on the farm!” Of course, if corn is going to cease being repeated on many acres in a forage program, replacement forages must replace some of the corn silage with something else. Not only that, but these forages must consist of large amounts of highly digestible fiber. At Forage Innovations, we design forage systems where corn silage is about half the diet and the other half are cool and warm (SxS) season grasses, small grains, and legumes more highly digested than alfalfa. We are often able to produce double the amount of digestible fiber per acre in the total forage production. One key is to always precede our corn with sorghum sudan, making corn always a first-year corn.
So, what can be the cause of this extra boost in corn silage production after SxS? There are at least four considerations which come out of the literature. And believe me, there is precious little literature that involved specifically corn following sorghum! Almost every crop from under the sun; from peas to peanuts, from lettuce to lentils and from pumpkins to watermelons had some research on these rotations involving SxS.
The first sorghum helper is the fact roots from sorghum are much more complex and fibrous than corn roots. If you would pull up a corn root and a SxS root and examine the amount of soil captured and retained on the SxS root system compared the corn, SxS captures abundantly more soil. The rhizosphere (area around a plant’s roots) will be more alive and active with soil-beneficial microbes. This root activity is what builds improved soil structure and water-holding capacity. All this is an advantage that the subsequent corn crop will benefit. Many times, the SxS fishing worm population (and this is highly scientific) is double and triple or more than the number in the corn root-system. All of this is an indication that the SxS rhizosphere is more alive with soil microbes in a mutually beneficial soil environment. SxS is a soil-life builder.
Biofumigation is a natural pesticide and in the example of corn, it especially works against corn rootworms. The constituent of SxS that provides this benefit is called dhurrin. Dhurrin is a weird name, but I guess when they named it, all the good names were already used up! Actually, dhurrin is derived from the Arabic word for sorghum. This mystery ingredient is the precursor to the formation of Prussic Acid which is something most people that have planted any sorghum product have heard. Prussic acid can be toxic to grazing animals if the crop is grazed right after a frost. However, the situation is widely understood, and few cattle are fatally affected. The acid is quickly dissipated with fermentation when harvested and stored.
Some of the literature simply states that SxS is a poor “host” for rootworms, but other work suggests that the reason for the unfriendly hosting is the cyanide poisoning from the prussic acid.
Exudates form the roots of SxS is largely made up of a natural allelopathic substance called sorgoleone (sor-go’-le’-own). Sorghum sudan is often planted as a break crop in short-term vegetable production to hold back weeds before the next crop. Allelopathy occurs when the allelopathy producing plant dies, is harvested, or incorporated. Don’t misunderstand and expect no weeds to grow during the establishment of the SxS. However, SxS establishes rapidly in warm soilsand has canopied soon enough if the field was clear of weeds to start .
One last benefit is clients of Forage Innovations (FI) typically precede corn not just with a sorghum sudan, but a cocktail mixture of SxS, Italian Ryegrass and various clovers or a similar mix depending on what climate the field is located. This mixture of roots adds more to the establishment of a beneficial soil structure, water-holding capacity and improved organic matter. Likewise, FI clients are having a built in cover crop on every acre. This mainstains the improvement in soil health.
Take advantage of these factors in your cropping rotations by contacting Forage Innovations at firstname.lastname@example.org or email@example.com and have us design a forage plan that works.