Soybean producers in Mississippi irrigate the third most acres in the U.S., 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 number of irrigated acres and amount of irrigation water applied to the major crops grown in the Delta. Most of this water is pumped from the Delta alluvial aquifer.
In March 2011, I posted a blog using 2010 data (see below table) that outlined how reducing the amount of irrigation water applied to soybeans could significantly reduce the amount of water withdrawn from the alluvial aquifer for that purpose. The numbers may have changed in the subsequent two years, but the facts have not.
Each year, the YMD also makes measurements throughout the Delta to estimate water volume changes in the alluvial aquifer. During the 2005-2010 period, 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 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 (OFWS), etc.
Three points about OFWS for irrigation purposes:
- This is not a new concept. In an Oct. 3, 1986, Delta Farm Press article (Vol. 43, No. 34, p. 1,5), this option was discussed at length and its utility was touted.
- Water captured in impoundment structures for future irrigation use provides positive downstream water quality benefits.
- Impounded water from winter rains 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 coming years to determine what route to take to reduce the amount of irrigation water applied to soybeans while still maintaining near maximum profitability, and to reduce dependence on water pumped from the alluvial aquifer.
- Determine the yield and economic effects of reducing seasonal irrigation amounts applied to soybeans over the usual irrigation period.
- Determine how and when irrigating with limited water will affect soybean yields and net returns.
- Determine the economic and water savings results from OFWS to offset irrigation water pumped from the Delta aquifer.
- Develop and/or identify new technology that can be used to increase irrigation efficiency.
The MSPB is actively and aggressively promoting and supporting water conservation in the Delta through its recently-initiated SIP 2014 initiative.
Also, the MSPB is supporting recent and continuing research and programs by Drs. Jason Krutz, Joe Massey, Mary Love Tagert, and others that will provide insights and protocol for the adoption of water conservation methods in the Delta. Results from these efforts will be posted on this website as they are produced.
I end this article with this: Identifying and adopting measures that can be used to conserve/reduce the amount of water that is used to irrigate Delta crops may not be the total answer, but it is a good and necessary start. And most certainly it beats the heck out of doing nothing.