Blog

An attorney from Virginia called recently to discuss whether soybeans can or can’t grow in hydric soils. He is representing a client in Virginia who has been successfully growing soybeans on hydric soils in a field which the Natural Resources Conservation Service (NRCS) recently decided was a wetland and can’t be farmed. However, according to the attorney, the soybeans yields coming off this parcel are about equal to yields on the rest of the farm and he and his client are contesting the NRCS decision.

The caller already knew that soybeans don’t like wet feet, since he is from Jacksonville, Illinois, and owns farmland there. He wanted to know more about how soybeans respond to saturated soils and whether hydric soils, the basis of a wetland, can also be farmable.

The first question is: “Are the soils hydric?” According to the NRCS, “(a) hydric soil is soil which is permanently or seasonally saturated by water, resulting in anaerobic conditions that change soil morphology and shift vegetation to water-loving plants, as found in wetlands.”

Along the Ohio River and Lower Mississippi Delta there are some areas in soybean production that aren’t artificially drained and have hydric soils because they can pond water for extended periods during the growing season during periods of high rainfall and river flooding. While these acres may have some characteristics of hydric soils, they are still farmable during many years and can produce exceptional crops.

I can assume that the NCRS deemed the soil hydric from a soil survey of the field in question and probably from an assessment of morphology and volunteer vegetation. We have some lowland areas on our family farm that have hydric characteristics but can still be farmed, though in some years they can be wetter than normal. However, it is hardly a wetland in my opinion and we can farm it but can’t drain it.

The NRCS description state: “A hydric soil is defined in the FSA as a soil that, ‘in its undrained condition, is saturated, flooded, or ponded long enough during the growing season to develop an anaerobic condition that supports the growth and regeneration of hydrophytic vegetation [16 U.S.C. 3801(a) (12)].’ The question is quite simply —without drainage (per the definition of drainage in the FSA procedures), would the soils be ‘saturated, flooded, or ponded long enough during the growing season to develop an anaerobic condition that supports the growth and regeneration of plants growing in (A) water or (B) growing in a substrate that is deficient in oxygen due to excessive water content.’ If so, the soil is hydric. If not, the soil is not hydric. A NTCHS hydric soil indicator from the hydric soil field indicator guide can be a vital tool in the decision-making process. Nearly all hydric soils exhibit characteristic morphologies that result from repeated periods of saturation or inundation that result in reduction of free oxygen (“anaerobic condition”). Saturation or inundation, when combined with macro and microbial activity in the soil (and use of oxygen by plants), causes the depletion of oxygen. Microbial activity is the ‘driver’ in the depletion of oxygen in most soils.”

The second question the attorney wants to address is: “If the soybeans are yielding so well, is the field really a wetland or just a hydric soil that can be saturated for short periods?” We all know the effects of short-term soil saturation on soybeans. During germination, it will reduce final germination and emergence. Research shows that a two-day flooding event after seed imbibition and swelling can reduce germination by 20 to 43 percent. And during early vegetative growth, early-season flooding will make soybean seedlings more prone to soil-borne diseases and will suppress nitrogen fixation.

When soybean fields become flooded oxygen for microbial and root respiration is limited, resulting in a negative impact on symbiotic nitrogen fixation and mycorrhizal colonization of soybean roots. For more information review “Flooding Impact on Crops” by Pioneer.

I have not seen the field in question nor the soil profile deemed hydric. However, from tracking the yield of soybeans, the crop seems to do just fine in most circumstances though the soil still has hydric characteristics. The question remains whether the attorney and his client will convince the judge overseeing the case the field and portion in question is farmable and not a wetland.

Soybean agronomist Daniel Davidson, Ph.D. posts blogs on agronomy-related topics. Feel free to contact him at djdavidson@agwrite.com or ring him at 402-649-5919.