FROM THE FARM REPORT: SOYBEAN AGRONOMY 101

Soybeans are not a commonly grown forage crop used by the dairy industry, and we’ve published very little content about the crop for that reason. However, more and more dairy farmers are taking an interest in soybeans as a potential cash crop, or as a homegrown grain source for their rations. This can be a very wise move from a financial standpoint since the price of soybeans can easily drive up the cost to feed cows. Based on reports from local agricultural lenders, dairy farms that sell crops in addition to milk have made considerably more profit in recent years than farms that sold milk alone.

The point of this article is not to convince you that you should be growing soybeans, but rather to provide some basic information about soybean agronomy for those who aren’t familiar with the crop.

For starters, soybeans are a legume. While I’ll mostly be comparing soybeans to corn, they’re more closely related to alfalfa. Since they both can fix nitrogen, crop nutrition for soybeans is generally like alfalfa. Likewise, herbicide carryover that injures alfalfa is also likely to damage a soybean crop. While soybeans do respond to nitrogen fertilizer, nitrogen is not recommended since soybeans have the ability to fix atmospheric nitrogen when properly inoculated. Be careful with heavy manure applications and pop-up fertilizer use with soybeans. The seed is very susceptible to high concentrations of salts that might be tolerated by corn.

Soybeans differ from alfalfa in that they are large seeded, enabling singulation and deeper planting. Regarding row spacing, soybeans are actually quite flexible. Row units on 30 inch centers work fine or they can be run as close as 7.5 inches apart through a drill. Narrower planting reduces weed pressure, but it makes the crop much more prone to diseases such as sclerotinia white mold.

When purchasing soybean seed, it’s best to buy only what you need. The seed doesn’t keep nearly as well as corn seed, and having to re-apply the nitrogen fixation inoculant on last year’s seed is both inconvenient and inefficient. When purchasing seed, it’s also important to note that the maturity rating for soybeans is different than corn. Soybeans are put into maturity groups ranging from 000 up to 8 while corn relative maturity ranges from about 75 – 125 days.

Regarding planting date and population, soybeans are also quite flexible. They generally want to be planted around the same time as corn. That being said, early planting translates to higher yields just as much (or more than) corn. The only caveat is that soybeans are more easily wiped out by frost than corn, since the growing point is exposed once they emerge. A good return on investment can be achieved with a plant population ranging anywhere from 100 to 200 thousand plants per acre. This flexible plant population and a greater tolerance of uneven emergence makes soybeans an excellent candidate for no-till planting.

Aside from a greater susceptibility to weed pressure and the need for a different herbicide and fertilizer program, the rest of the growing season for soybeans isn’t much different than corn. The timing of harvest can work out nicely for dairy producers, since soybeans of the proper maturity group are likely to be ready for harvest just a little after optimally-timed corn silage.

To be utilized by livestock, soybeans must first be roasted to deactivate the trypsin inhibitor and pressed to reduce the oil content. While vegetative soybean plants can be of reasonable quality, the fiber digestibility of reproductive soybean stems is absolutely terrible. While some farms do attempt to bale soybean straw, I wouldn’t expect it to be suitable for anything more than bedding – assuming you can handle the dust.

— Allen Wilder

wilder@whminer.com