On average, the Mid-South receives abundant annual rainfall to produce good yields and high quality for numerous field crops.
Rainfall timing, however, plays a more important role in crop production than yearly accumulations. Crop water demand is typically concentrated when rainfall is less certain.
In some seasons, too much water poses a bigger threat than not enough.
“Rainfall rarely occurs at the right time, in the right location, and in the right amounts,” says Stacia Conger, Extension irrigation specialist, LSU Red River Research Center, Bosier City, La.
Conger discussed the basics of efficient irrigation for Mid-South farmers at the annual Louisiana Technical Management Conference in Marksville, La., earlier this year. In follow-up communications with Delta Farm Press, Conger offers a more detailed analysis of the need to develop more efficient irrigation systems throughout the region.
In the first of a three-part series on efficient and effective irrigation, Conger discusses advantages of a well-designed and well-managed irrigation program. Other segments will consider the tools available to improve moisture management and the next steps needed to increase awareness and availability of information.
Why do Mid-South farmers need to be concerned about water conservation with usually abundant rainfall?
Irrigation should be supplemental to rainfall during critical growth periods to minimize water stress in hopes of maximizing yield and quality. We think of irrigation as insurance against drought with the misperception that you cannot irrigate too much.
Too much water can cause crop stress from prolonged lack of available oxygen in waterlogged soils. It also creates prime conditions for disease, pests, and weeds. If applied from the surface in large amounts (i.e. flood vs. subsurface drip), irrigation can contribute to long-term problems to soil health, such as soil compaction.
Rainfall is inconsistent. It may be easier to schedule irrigation in the arid western states. Mid-South rainfall can be highly unpredictable, which makes irrigation scheduling important to on-farm water management.
How does energy cost savings fit into the equation?
The concept of sustainable irrigation is both environmental (water quantity and quality) and economical (maintaining profitability).
Most irrigation costs are consistent. Farmers do not regularly move wells or risers or change field shapes or sizes for irrigation. They buy the same amount of polypipe each year or replace about the same number of sprinkler nozzles for center pivot maintenance.
The largest controllable variable in irrigation cost is the number of irrigation events during the season, based on rainfall variability. Most agricultural water consumption is from groundwater, so farmers run large lift pumps that take a significant amount of fuel.
The irrigation season is less than four months for agronomic crops, so being able to hold off on irrigation by a few days to catch a rainfall on a few occasions can shift the schedule, so less irrigation is required.
Our economist estimates average energy cost savings from skipping one irrigation is $8 to $12 per acre, averaged across energy types and water sources.
It’s possible to go from eight events to five events in a normal year by scheduling properly. On a 1,000-acre farm, that’s $24,000 to $36,000 in savings in one year.
How about runoff and off-site movement of soil and nutrients?
We haven’t done enough work on this topic in Louisiana. We know, from research conducted elsewhere, that surface irrigation affects movement of soils and nutrients. We don’t know if changing irrigation practices will make a difference because of this region’s annual rainfall.
Last year, during the lengthy drought, we saw irrigation initiated much earlier than usual and heard more about increased nitrogen losses.
I would hypothesize that furrow irrigation, given its stream-like flow down the furrows, would increase soil and nutrient mobility compared to rainfall, if the rainfall is less than a certain volume and intensity threshold. I just don’t know what the threshold would be.
Many soil health initiatives — no-till, residue management, and cover cropping — slow nutrient transport. Applying fertilizers in multiple applications throughout the season also should help. Hopefully, agronomic research currently being conducted on soil health will quantify the difference in water quality from these various soil health practices.