The Changing Furrow-Irrigated Rice Paradigm

⋅ BY DR. CHRISTOPHER GARRETT HENRY ⋅
University of Arkansas Division of Agriculture

To grow rice in levees or on furrows is a paradigm change for many Mid-South rice farmers. The attraction of reduced labor and machinery operations is very appealing to them. Worn down beds from the soybean crop are about the perfect height for a furrow rice crop and ready to plant without any fall or spring prep work.  Some Arkansas growers have completely converted all of their acres from flood to furrow.

As appealing as rice on furrows can be, we have documented a 16 bushels per acre yield penalty and no significant difference in water use between furrow and flood systems. When using Multiple Inlet Rice Irrigation and compared in farmer fields side by side, this reduction shows up across five years. This yield penalty and the additional challenges and time commitments of irrigating row rice about twice as often as other row crops is challenging.

Additional disadvantages are heavy reliance on preemergent herbicides and possible higher nitrogen costs. Don’t expect farms that are a challenge to irrigate in a flooded system, to do better as a FIR field; the better the soil type and land grade is suited for flooded rice, the better it will perform as a furrow field. Often, there is the misconception that a field that is steep at the top of the field will somehow do better as a furrow field, when it’s just as much a challenge to irrigate as a flooded field.   

One problem I have observed early on in researching FIR, is that it is difficult to irrigate and soak across the beds effectively. Then as the season goes on, it becomes even more challenging because the soil seals and the rice demands irrigation more frequently. Without rains like we experienced in 2022, growers often fall behind, using up the stored soil water. The lack of water at this critical time is likely one of the causes for the yield penalty. Because of the shallower rooting zone relative to other row crops, it requires more frequent irrigations and, in some soils, each time becomes more difficult to fully wet the bed than the irrigation before.

So, I thought, since rice grows well in saturated soil, why not continuously irrigate furrow rice? This is what our pit-less system does, and the water management is similar to a flooded field. Without this system, we found that while most growers irrigate every three to seven days, in some cases, every day or every other day irrigation would be necessary to keep up with demand.

Merritt McDougall, a former graduate student of Chris Henry, standing in an Arkansas row rice field with Autonomous Pivot, an irrigation system that assesses soil moisture and crop health.

The potential benefits of furrow irrigated rice are many — less tillage, less equipment, fewer field passes, the ability to use cover crops and no-till, and improved soil infiltration from reduced tillage. The disadvantages include the loss of the flood as a weed control tool. While we have documented a yield penalty, we think that this is something that can be overcome. During a row rice roundtable, farmers told us they are willing to accept a 10-15 bushels per acre yield penalty and that the reduced need for tillage and labor were the main reasons for considering FIR. The yield penalty can be offset by the extra tillage and labor costs if one can manage post weed management effectively. The ability to utilize cover crops is a big advantage for FIR, something that could help with infiltration, water-holding capacity, nitrogen cycling, and weed suppression.

For those first starting out, water management is going to be more challenging. We suggest a soil moisture monitor to help determine irrigations, as rice water use is deceiving. Most farmers irrigate every three to seven days, but in the late vegetative and early reproductive stages, rice has periods of intense water use and even three days may not be often enough for those growth stages. Sensors also help the grower understand the water demand of furrow-irrigated rice. Those who have closely monitored a row rice field using a soil moisture monitor have come to realize these high-water-use periods and how effective or ineffective their irrigation changes as the season progresses. This adaption during the growing season can really help stay ahead of the irrigation and may reduce the yield penalty.

In 2023 we added rice to our “Arkansas Soil Sensor calculator” mobile app that is available on the Apple App Store and Google Playstore, published by the University of Arkansas Water Management Team. The app helps with scheduling decision-making, providing the days between irrigation and when to start and stop.

With FIR, there is more flexibility in planting because tillage and field preparation needs are greatly reduced. Some plant with the furrows, some at an angle, some plant flat and pull the beds after. There is a need for better equipment for FIR. Growers will need to experiment with the equipment they have and find the technique that results in the best stand. A Clearfield hybrid, a field with a history of low weed pressure and a ground-rig available, and a Greenseeker with a reference area(s) in the field are other tools that will aid in learning FIR management.

Finally, we have developed and demonstrated new production practices centered around the pit-less pump. In the near future, automation we have developed on should greatly reduce the trips to the hydrant and maintain soil moisture at an optimum level. The data shows the system can improve yield in dry years like 2022 by 24 bushels per acre over conventional FIR irrigated every three days while using 56 pounds less nitrogen in a dry year. In wet years, the yield difference can be insignificant, so the pit-less system provides yield stability using 40%-60% less irrigation water. 

Conventionally irrigated furrow rice is going to be a challenge to be climate smart because of the water use and the challenge of controlling methane emissions in the flooded tailwater area and top of the field where nitrous oxide emissions will occur from the wetting and drying.  Whereas the pit-less system can keep the entire field between saturation and field capacity while still having irrigation water use in line with zero grade fields (<19 ac-in/ac).

Expect to see more on our efforts in the next few years. NRCS has recently approved the pit-less pump for incentive payments, so expect to see more pit-less pumps on the landscape in the near future. Support of our research to improve the FIR system has been provided by the Arkansas Rice Research and Promotion Board, the Arkansas USDA Natural Resource Conservation Service, RiceTec, Yara, FMC, Bayer, Gowan, ADAMA, Syngenta, Delta Plastics, UPL, BASF, Nutrien (ESN and seed division) and OxPipe have all supported the efforts of my program to develop and improve the FIR system. Without the support of the rice board and the check-off, such improvements, new ideas, and the development of the pit-less system would not have been possible.

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