The art of irrigation begins now

The art of irrigation begins now

justin chlapecka
Assistant Research Professor/
Rice Extension Specialist
University of Missouri

The time we’ve all been waiting for is finally here. While I write these comments on March 29, there are already several thousand acres of rice planted across the Missouri bootheel. In fact, we got our first planting date study in the ground 12 days ago on March 17. To no one’s surprise, the seed still looks exactly the same as it did when it came out of the bag. Regardless, it’s nice to feel like we are making a little progress on the 2022 rice crop. 

There’s no better time than now to begin thinking about water management. Last year, about 30% of Missouri rice acres were furrow irrigated. When preparing to plant furrow-irrigated rice, there’s a fine line on bed size. We want to make sure there’s enough of a furrow that we don’t have water breaking over, but at the same time not too deep of a furrow so that water will not adequately wick across the beds. As if any of us didn’t know, it’s hard to move water upward ­— at least when we want it to! 

While beds should be prepared prior to planting on our silt loam soils, the heavier Sharkey clay seems to perform better when planted flat. Shallow water furrows can then be created sometime between emergence and the first irrigation event. It seems like the later the better within that time frame. The reason for this is simple. Heavy clay has plenty of potential to wick across. So even if we have a furrow that doesn’t work out, that can be overcome, whereas on a silt loam or lighter soil, we don’t have that luxury. 

If you have a field where getting the water wicked across for your soybeans is difficult, you’re not going to enjoy furrow-irrigated rice. We’ve tried it multiple times. Unless you want 100 bu/ac rice, I’d suggest not trying furrow irrigation. Rice, especially hybrids, can take much greater water deficit stress than most of us realize. But ultimately, we’ve still got to get the water to it when summer comes along and those soils that seal over can become a real hassle. 

If we set ourselves up good on the front end, we’ll be much happier with a yield map lacking those dreaded red streaks. If you’ve got any questions, don’t hesitate to give me or your local expert a shout. As always, eat Missouri rice! 

Efficient rice irrigation

Jarrod Hardke, University of Arkansas
Professor/Rice Extension
University of Arkansas Cooperative
Extension Service

By flood or by furrow, efficient irrigation will be an important key to rice profitability in 2022. Given the rise in input costs, minimizing our time and energy expenses related to irrigation should be an even bigger priority than usual.

Multiple Inlet Rice Irrigation (MIRI) continues to be an underutilized practice. Many cite the cost of the pipe and the time required to install it as the main limitations to adopting the practice. However, the 2022 season is a prime opportunity to put this practice in place and reap the greatest benefits.

Diesel prices this year have the potential to increase irrigation costs by $50 per acre compared to 2021. That kind of increase makes it simple to pencil out the cost of polypipe and installation. Budget numbers may be closer using electric pumps, but electricity costs have been increasing as well.

Arkansas rice specialist Dr. Jarrod Hardke said if you are not using sensors, a generalized irrigation approach could be to irrigate every three to five days on silt loams or every five to seven days on clays.

While we do have increased labor costs for installation, that effort is balanced out by only needing to set levee gates one time. There is no longer a need to “close up” fields following the first flooding event. When using MIRI, the aim is to set the gates (rods) high for emergency spill-over and to be able to capture rainfall events.

The goal with MIRI is to flood up each individual paddy and not cascade any water through the gates unless there is an extreme rainfall event. This means less in-season gate management because we don’t want to let water flow through them. Instead, we’re adjusting the water flow going into each paddy from the polypipe — a much simpler adjustment.

Current estimates are that using MIRI can reduce irrigation labor by 30% and pumping by 25% or more, depending on the soil and situation.

To include a few comments on furrow-irrigated rice — avoid overwatering. That may sound strange to many, but we do observe more issues with overwatering furrow-irrigated rice than you would think, especially where cold well water is the irrigation source.

Rice doesn’t require a flood; we just need to avoid water stress. Most importantly, avoid water stress during reproductive growth from panicle initiation through grain fill. You may also want to irrigate a final time around when you would normally drain a flooded field — just to ensure adequate moisture to carry the rice to maturity.

If using soil moisture sensors, place them approximately one-third of the way down the field in the top of the bed. If not using sensors, a generalized irrigation approach could be to irrigate every three to five days on silt loams or every five to seven days on clays.

Use a computerized hole selection program to help with MIRI or furrow-irrigated rice irrigation setup. Contact your county Extension agent or a specialist if we can help.

Bugs to watch out for in 2022

Luis Espino
Dr. Luis Espino 
Rice Farming Systems Advisor
University of California Cooperative Extension

The 2022 season is going to be an unprecedented one for rice growers in California. The drought is going to significantly reduce acreage and may affect the crop in other ways, including arthropod control.

Given the reduced availability of water and the dryness of fields, we are set up for slow flood-up in the spring. This may exacerbate problems with tapdole shrimp. Longer flood times allow the shrimp to hatch and grow to a size that can injure rice.

Typically, rice can escape shrimp injury if it gets established (with a well-developed green spike and a 1-inch root in the soil) before the shrimp’s shell reaches the length of a rice seed. Once rice is well established, even large shrimp won’t injure it.

When tadpole shrimp shell size is about the size of a rice seed germinating, rice seeds can be injured.

This year, make sure to be extra careful in fields that take a long time to flood. If small shrimp are present before or right at seeding, a treatment is needed. Also, keep in mind that lambda-cyhalothrin, the main insecticide used for tadpole shrimp, is now being monitored at the same drain sites used to monitor for thiobencarb. Growers should be careful when spraying next to drains and observe water-holding times.

The second pest of concern is armyworms. The question I got several times during our winter meetings was if there was any way to predict if armyworms were going to be a problem this year. Unfortunately, I do not know of any way to predict if 2022 will be an armyworm year. The big armyworm outbreak of 2015 happened on a year of reduced acreage and after several years of drought. We are facing a similar situation in 2022.

I will set up the armyworm trapping network again this year and update the industry when moth counts start to increase. Even though moth counts don’t always correlate with worm populations, we have learned that one or two weeks after we reach the moth peak is when we see peak worm activity in the field.

The network is a great tool to determine when to monitor for worms and defoliation so that we are not caught off guard like we were in 2015.

Water-seeded rice

ronnie levy
Extension Rice Specialist
Louisiana State University

Most rice is drill-seeded in Louisiana — about 80% — but there is a renewed interest in water-seeding rice for weedy rice suppression.

The most common water-seeding method in Louisiana is the pinpoint flood system. After seeding, the field is drained briefly. The initial drain period is only long enough to allow the radicle to penetrate the soil (peg down) and anchor the seedling. A three- to five-day drain period is sufficient under normal conditions. The field then is permanently flooded until rice nears maturity (an exception is midseason drainage to alleviate straighthead under certain conditions).

In this system, rice seedlings emerge through the floodwater. Seedlings must be above the water surface by at least the 3 to 4-leaf rice stage. Before this stage, seedlings normally have sufficient stored food and available oxygen to survive. Atmospheric oxygen and other gases are then necessary for the plant to grow and develop.

Louisiana rice specialist Dr. Ronnie Levy said there is renewed interest in water-seeding in the state to suppress weedy rice.

The pinpoint flood system is an excellent means of suppressing weedy rice emerging from seeds in the soil because oxygen necessary for weedy rice germination is not available as long as the field is maintained in a flooded (or saturated) condition. A continuous flood system, another water-seed system, is limited in Louisiana. Although similar to the pinpoint flood system, the field is never drained after seeding.

Regarding the water-seeded systems, a continuous flood system is normally best for red rice suppression, but rice stand establishment is most difficult. Even the most vigorous variety may have problems becoming established under this system. Inadequate stand establishment is a common problem in both systems.

These emerged rice seedlings are ready for pinpoint flood.

Fertilization timing is the same for both the pinpoint and continuous flood systems. Phosphorus (P), potassium (K), sulfur (S) and zinc (Zn) fertilizers are applied preplant incorporated as in the dry-seeded system. Once the field is flooded, the soil should not be allowed to dry.

If the nitrogen requirement of a particular field is known, all nitrogen fertilizer can be incorporated prior to flooding and seeding. Otherwise, one-half to two-thirds of the estimated nitrogen fertilizer requirement should be incorporated prior to flooding and seeding or applied during the brief drain period in a pinpoint flood system. Additional N fertilizer can be applied at midseason at the beginning of reproductive growth between panicle initiation and panicle differentiation (2 millimeter panicle).

Water-seeding has been used in the past for weed control. Will water-seeding make a comeback to help with weedy rice suppression?

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