Water-use efficiency options

Rice Extension Agronomist
University of Arkansas,
Division of Agriculture

“Do I have an adequate water supply to irrigate the rice acreage I intend to grow?” This should be one of the first questions a rice grower asks before the season begins. For optimum rice production, we need sufficient water availability to be able to flush a field in two to four days, achieve a permanent flood in three to five days and be able to maintain a flood for the entire season. Of course, rice can be grown effectively with less than these optimum water management conditions, but these are good irrigation guidelines for producing high-yielding, high-quality rice.

Water-pumping capacity is usually spoken of in terms of gallons per minute (GPM) per acre, or GPM/acre. Depending on soil type, the minimum pumping capacity needed to achieve the irrigation capabilities mentioned earlier is a minimum of 10-20 GPM/acre, with an optimum range of 15-25 GPM/acre (lower numbers for silt loam soils, higher numbers for sandy soils).

To put that to work on the farm, a well capable of pumping 2,000 GPM should be able to successfully irrigate a 200-acre silt loam field, a 133-acre loam or clay field or a 100-acre sandy field. Average seasonal water use for different soil types ranges from 24 to 48 acre-inches. At 27,154 gallons per acre-inch, you would need 814,620 gallons of water per acre to sufficiently water rice grown on a silt loam soil with no pan (30 acre-inches).

“How can I reduce my water use while maintaining yield?” Management options are available to improve water-use efficiency in rice production. Multiple inlet irrigation can be useful in delivering irrigation water evenly across a rice field at one time; allow for faster flooding; and reduce costs associated with pumping and irrigation labor. Many rice farmers in Arkansas use multiple inlet irrigation, but there are many more acres where this practice will work – fields with contour levees can use multiple inlet in addition to those that are precision-leveled or zero-grade. Intermittent flooding is another possible water management option but needs more study before it becomes a recommended practice in Arkansas.

“What about flushing?” For a number of reasons, early season flushing of your rice crop may be necessary. Establish levees and install levee gates as soon as possible after planting to allow for flushing if it is needed for stand establishment or herbicide activation. Being able to flush quickly is very important in order to maintain an even stand and proper herbicide activity. Any delays could ultimately result in yield loss and loss of weed control.

Remember to plant an amount of rice acreage you can irrigate properly, ensure your pumps are serviced, be prepared to flush if necessary and minimize practices that lead to runoff water.

Fresh water supply


Looking back at the past two seasons shows major contrasts in water issues from one year to the next. In 2011, conditions were dry enough to cause concern about salt water and require irrigation of upland crops while the Mississippi River was threatening to overflow its levee system. Last spring heavy rains caused a significant number of rice farmers in southwest Louisiana to switch from dry seeding to water seeding rice as the planting season was delayed.

In January of this year, we got flood rains (in some cases a 300-year-flood, according to weather services) over a widespread area of the state. The experience of last year and the warmerthan- normal temperatures in January and some of February helped some farmers make quick decisions to water seed rice rather than wait for things to dry up and dry seed. As of the second week of March, reports are that as much as 30 percent of our rice acreage has been planted, and we could have half of our acreage planted by March 15.

An abundant supply of fresh water, whether from rainfall or surface supplies or wells, is essential to rice production. I continue to read about experiments with various systems of upland rice production under sprinklers, which in south Louisiana would likely make last year’s blast epidemic look mild compared to the amount of blast we would have under those conditions. Our varieties are simply not designed for upland production.

A couple of months ago, I got a phone call from an attorney in a neighboring state who wanted to hire me as a consultant to teach farmers how to grow upland rice. He was not interested in agriculture. He was interested in preserving water supplies in reservoirs built for irrigation and flood control, but now surrounded by high-dollar real estate development. My response? “You’re talking to the wrong guy.” Asking growers to switch from paddy rice production to upland rice production without the research to support the switch is at the very least unreasonable.

Over 15 years of our Rice Research Verification Program have certainly verified one thing to me; water management is the single most important factor in rice production. The ability to get water on and off the field in a timely manner and maintain an even flood is the most important facet of rice production. The advent of laser leveling has been a major contributor to solving problems in water management. Precision leveling land and the resulting improvement in water management may be the most important production practice under the control of the grower.

Water: Old, but valuable chemistry


It has been a dry winter and spring in California. Presently the two major reservoirs that supply irrigation water to the rice fields of the Sacramento Valley, Lakes Shasta and Oroville, stand at 82 percent of capacity. Taken alone, this is not particularly troubling; these levels are common for this time of year. However, the snow pack depth in the northern Sierra Nevada is only 60 percent of the long-term average and at only 45 percent of historic average depth in the southern Sierra.

The major reservoirs that supply agriculture in the San Joaquin Valley are at less than 60 percent of capacity on average. The water supply in the Sacramento Valley will likely be adequate to supply the needs of local rice production. However, the sparse water supply in the southern part of the state may encourage the selling of surface water and idling of the associated rice land. Water sales put downward pressure on the number of planted acres.

Another result of the dry spring is that field operations are about two weeks ahead of the “normal” schedule. There are advantages to planting early. Yet, if planted too early with cool temperatures (air and water), seedling establishment will flounder. Remember, below about 55 degrees F, California varieties grow very slowly, if at all; a high temperature of 70 degrees F does not mean there are adequate heat units to drive vigorous growth. Plant growth stalls and the seedlings become chlorotic when exposed to extended periods of cool temperatures. While it is tempting to add more fertilizer to a struggling field, often all that is needed is warm weather to solve the problem.

Once the decision to plant is made, flood your fields as quickly as possible in preparation for seeding. A prolonged flood-up creates a disparity in weed seed germination across the field. The weeds get a head start on the rice in the upper checks when field are slow to flood. There can be a range of weed development from the top to the bottom of the field that compromises herbicide efficacy. Also keep in mind that in cold irrigation water intake checks, the weeds (and rice plants) may lag behind in development compared to the rest of the field.

Water management is a key component of a weed management strategy. Water is old chemistry, but extremely valuable. Water suppresses watergrass growth and improves herbicide effectiveness. If you must drain, reflood as soon as possible. Short drains shift weed population characteristics and favor the grass weeds. In a drained field, the nitrogen (N) loss begins when the soil is still saturated with little or no standing water. The N loss begins long before the soil cracks. The “starter” fertilizer applied to the surface is the most susceptible to loss during the drain periods.

Finally, pay close attention to the herbicide specific water-holding period and application practices. The water quality downstream from the rice production area continues to be monitored for rice pesticides. Now more than ever, sound management practices that help preserve water quality are vital to the long-term interests of the industry.


New reservoir?

Rice Research Entomologist

As you know, I am not a water management scientist, but I do know the importance of water to Texas and U.S. rice production. Our producers are well aware of the value of this precious resource because of its necessity, cost, environmental benefits and scarcity.

You are probably aware of the devastating drought in Texas in 2011, which resulted in about a 50,000-acre drop in rice acreage in 2012. Basically, rice production in Colorado, Wharton and Matagorda Counties was drastically reduced in 2012 because water levels in Lakes Buchanan and Travis northwest of Austin were below a release trigger established by the Lower Colorado River Authority (LCRA) for “interruptible” water (agricultural use).

Unfortunately, lake levels as of March 1, 2013, were below 850,000 acre-feet, which means the same water restrictions in 2012 will apply to our rice farmers this year. The Colorado Water Issues Committee (CWIC) chaired by Ron Gertson, who is a rice farmer in Wharton County, represents rice interests dealing with Colorado River water issues. The CWIC takes a science-based approach to proposing solutions that are fair to all competing parties (municipal, industrial and agricultural).

However, the Central Texas Water Coalition (CTWC) representing lakeside interests, has proposed solutions which would have devastating consequences to the long-term viability of our rice industry along the lower Colorado River. Among these proposals are raising water rates to exorbitant levels for rice farmers and forcing farmers to abandon rice farming by buying land to remove from rice production. These lakeside interests complain rice farmers’ irrigation water is heavily subsidized and “a cost of less than $7 per acre- foot for irrigation purposes” while, in reality, the cost is over $40 per acre-foot.

They criticize the amount of water needed for rice production, but ignore the fact that Austin dwellers use an equivalent amount to water their lawns! These lakeside interests are reaping the economic benefits of high-value lake property and associated recreational activities, which are due to the original construction of these lakes agreed upon by agricultural, municipal and industrial interests.

In short, LCRA now realizes the need to capture, store and provide more water for all users. To this end, LCRA is proposing construction of a reservoir along the lower Colorado River near Lane City in Wharton County. This reservoir, with a surface area of over 1,100 acres, will increase the supply of LCRA water by about 90,000 acre- feet. The total cost of this project is estimated to be about $200 million and will be funded by grants, loans and other sources. As Ron Gertson says, this is “thinking outside the box” to make sure our rice
industry has a reliable source of water in the future.

Water quality testing

Agronomy Specialist

An abundant supply of good quality irrigation water is needed for optimum rice production, and the Missouri Bootheel is blessed with an abundant supply. Thirty acre-inches of irrigation water pumped per year is average for Missouri rice fields. Our water supply is very good and relatively inexpensive to lift to the surface, but it costs money and fuel to do so. Rice is normally flooded at the fifth leaf or first tiller, and a flood is held the entire season.

Yearly preplant field leveling or smoothing is essential for seedbed preparation, surface drainage and maintaining optimum flood depths. A landplane or float should be used to remove reverse grades, fill “potholes” and smooth out old levees, rows or ruts in a field. Rice can germinate under either soil or water, but not both. Therefore, maintaining a field surface that provides good drainage is important for stand establishment; controlling weeds, diseases and insects; maintaining desired flood depths; and providing a dry field for harvesting. A water supply is adequate for a given field if you can flush in two to four days, flood in three to five days and maintain a flood for the entire season.

We have isolated water quality and quantity problems in our Missouri rice fields. Knowledge of the quality and quantity of irrigation water is required for proper water management and high-quality, high-yielding rice. Correct diagnosis of problems concerning irrigation water quality is critical for effective management. Water quality testing is an important step in diagnosing existing problems and identifying potential problems.

Samples can be taken and tested at the University of Missouri Soils Lab at The University of Missouri Delta Center at Portageville. For further information on taking a well sample, call Dr. David Dunn, University of Missouri Soil Lab, (573) 379-5431 or Sam Atwell,
Agronomy Specialist, (573) 429-9141.

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