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Irrigated Soybeans In The Delta—What Is The Future?

Soybean producers in Mississippi irrigate the third most acres in the US, second only to Nebraska and Arkansas.  The vast majority of these irrigated soybean acres are in the Delta.


Each year, the Yazoo Mississippi Delta Joint Water Management District (YMD) estimates the numberof irrigated acres and amount of irrigation water applied to the major crops grown in the Delta.  Most of this water is pumped from the Mississippi River Alluvial Aquifer. Data for 2010 are shown in the below table.  It is obvious that irrigation water applied to soybeans is a significant amount of the total applied.
















































Crop Estimated irrigated acreage Estimated water useper acre (acre-ft.) Estimated water useper crop (acre-ft.)
Corn 297,300 0.8 (9.6 in.) 237,840
Cotton 170,518 0.7 (8.4 in.) 119,363
Rice 308,523 3.4 (40.8 in.) 1,048,978
Soybeans 904,808 1.1 (13.2 in.) 995,289
Aquaculture 38,573 3.0 (36 in.) 115,719
Total 2,517,189
Data provided by Mark Stiles, YMD, Stoneville, MS.

Each year, the YMD also 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 is a matter of concern. In a recent Delta Farm Press article, Dr. Dean Pennington, Executive Director of YMD, gave an update on the state of the alluvial aquifer. He outlined numerous changes to permit regulations that took effect on Jan. 1, 2011 to abate the aforementioned decline in the aquifer and ensure its sustainability. His bottom-line message as reinforced by the new water conservation regulations guiding the permitting process is that the continued overuse of water from the aquifer cannot continue. The changes he outlined deal with the physical aspects of irrigation management; i.e., land leveling to zero grade, reducing runoff and/or recapturing excess irrigation water, on-farm surface water storage, etc. Two points about impounding surface water for irrigation purposes.

  • Water captured in impoundment structures for future irrigation use provides positive downstream water quality benefits.

  • Impounded water can be used for early irrigations, thus reducing the amount of groundwater needed or used for irrigation during the season. This conservation measure is currently being evaluated to determine just what the savings will be for a given amount of land that is 1) irrigated, and 2) used for impounding water.


There are other options that can be considered for reducing the decline in the aquifer water level. First and foremost is the application of less irrigation water to meet crop needs. 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.


What will be the ramifications of cutting irrigation by these amounts? That is hard to say, but there is over 20 years of irrigation research data from Stoneville to indicate that on average no more than 11.5 in. of irrigation water are required to achieve maximum yield when soybeans are planted before May 1. Also, if plantings are made in the first half of April, it is estimated that on average only about 7.5 in. of irrigation water will be required to achieve maximum yield. Both of these amounts are well below the 13.2 in. of irrigation water estimated to have been applied to soybeans in the Delta in 2010. So simply managing planting date can minimize the amount of irrigation water needed to irrigate soybeans for maximum yield. There is another option that may be harder to swallow–irrigating with limited water. This concept is explained in an article on this site, and in an updated article published by Colorado State University. It may be what is down the road if irrigation and crop management practices for water conservation are not widely adopted or are not successful on a wide scale in the Delta over the next few years. Several 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 soybeans over the usual irrigation period.

  • Determine how irrigating with limited water will affect soybean yields and net returns.


While neither of these options may be acceptable in the short term, they may be required for the long-term sustainability of the alluvial aquifer. An additional point: Both of the above research approaches will require an investment in rainout shelters to control the research environment. To paraphrase a past TV commercial’s catchphrase, “We can sacrifice a little now, or sacrifice a lot later”.


Recent postings of articles on this site are:


*I thank Mark Stiles and Dean Pennington for reviewing this article.
larryheatherly@bellsouth.net.