Sustainable Soybean Production—Part VII

Producers growing soybeans in Mississippi irrigate the third most acres in the US, second only to Nebraska and Arkansas. The facts about irrigating soybeans in Mississippi include:

• The vast majority of the irrigated soybean acres are in the Delta;


• Properly irrigated soybeans will yield at least 20 bu/acre more than nonirrigated soybeans;


• Properly irrigated soybeans will be more profitable than those not irrigated;


• Amount of irrigation water applied to soybeans is a significant portion of the total applied to Mississippi crops; and


• Most of the water used for irrigating Delta soybeans is pumped from the Mississippi River Alluvial Aquifer.

Each year, the Yazoo-Mississippi Delta Water Management District (YMD) makes measurements throughout the Delta to estimate water volume changes in the alluvial aquifer. Over the last six years (2005-2010), the estimated change in the aquifer level averaged a loss of about 234,000 acre-ft/year–the change was negative in 5 of the 6 years. In fact, over the last 24 years that these measurements have been made, 15 years have shown estimated declines in the aquifer level

Obviously, this adds two more facts to the above list.

• The current level of water extraction from the alluvial aquifer is not sustainable, and


• Both physical and management changes must occur to sustain irrigation as a viable management practice for growing soybeans in Mississippi.

Physical changes that can help change this trend include land leveling to zero grade, reducing runoff and/or recapturing excess irrigation water, and using water from on-farm surface water storage structures and/or impoundments.

Management changes will rely solely on applying less water to soybeans during the growing season. Consider the following.

• If soybean irrigation in the Delta is cut by 1 acre-inch each year, an estimated 75,666 acre-ft. of water will be conserved.


• If soybean irrigation in the Delta is cut by 2 acre-inches each year, an estimated 151,333 acre-ft. of water will be conserved.


• If soybean irrigation in the Delta is cut by 3 acre-inches each year, an estimated 227,000 acre-ft. of water will be conserved. This amount is essentially equal to the average drop in the aquifer over the last 6 years.

Another option that may be harder to accomplish is irrigating with limited water. This concept is explained in an article on this site. It may be what the future holds in the Mississippi Delta if irrigation and crop management practices for water conservation are not widely adopted or are not successful on a wide scale over the next few years.
Recently, a producer friend of mine emailed me with a novel approach (not to him) to the above. His comments to me (with some editing) follow.

“You may recall that years ago I asked you for a steady source of information on non-GMO MG 3 soybean trials. You might recall that my rationale was that I didn’t wish to irrigate soybeans because it was expensive, we often yielded nearly as much by not irrigating, and someday we might be faced with aquifer problems. You suggested I peruse Midwestern university trial results. After a few trials, I settled on mainly University of Illinois information, and now annually order all seed from seedhouses there. The last two years, we have had to irrigate to get a respectable crop. Although my yields may not be the area’s best, they are near the top and are economically and sustainably more viable to produce. Last year, many that looked rather poor yielded 50 to 55 bu/acre, and this year that same rather shabby appearance yielded between 65 and 83 bu/acre. The key is they are planted at rates between 260 and 400 thousand seeds/acre, with expected stands of 10-15% less than that. This forces them to grow upward. They are planted flat with water furrows every 80 ft. to allow drainage and irrigation flow down the field. In the driest of conditions (and I have had them) on land rotated with rice or corn, they require only two irrigations. If this could be adopted on a wide scale, it could be an important part of conserving the Delta’s aquifer.”

This may be the type of new approach that is needed to sustain soybean irrigation capability in the Delta.
Three research approaches are needed in the next five years to determine what route to take to reduce the amount of irrigation water applied to soybeans while still maintaining near maximum profitability.

• Determine the yield and economic effects of reducing seasonal irrigation amounts applied to normal soybean plantings over the usual irrigation period,


• Determine how and when to irrigate with less water during the irrigation period in order to minimize or negate the effect on soybean yields and net returns, and


• Determine if a new paradigm is needed for growing soybeans that are to be irrigated as per the above email to me. (Of course, I recognize that the above specific approach cannot be presently adopted on a wide scale because 1) there will not be enough seed of non-GMO varieties, or 2) seed of GMO varieties likely are not affordable at the above seeding rates).

While none of these options may be acceptable in the short term, they may be required for the long-term sustainability of the alluvial aquifer and subsequently the future availability of water for soybean irrigation.
When it comes to irrigating soybeans in the Delta, the new thinking will necessarily become “how to produce a maximum sustainable yield rather that how to produce maximum yield”. Research will be required and should be planned and conducted to determine how to accomplish this on an economical scale.


larryheatherly@bellsouth.net.