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Water Management
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From dry planting to water-seeding.

Last year I wrote an article on water management on March 29. Following is most of the first paragraph of that article. I had no idea at the time of how much of it would be accurate and how different it would be this year. “While I have not had any calls about salt water this year (2011), if it remains as dry as it has been since January, they will come in. At this writing, most of the rice in the southwestern area is planted, much of it drilled, and waiting for rain or a flush. When everyone cranks up their pumps around the same time, the supply of fresh surface water is likely to become critical in some areas.”

That was last year.

Until a month or so ago, we were still concerned about fresh water. Thanks in part to two major rainfall events, the first dumping from one to six inches of water over the course of a couple of days and a more recent event that soaked us with from two to 15 inches of water in a 12-hour period. Most of the flooding problems were in an area just north of Lafayette and not a major rice-growing area. However, the runoff is still moving south, and a lot of farmers are behind in their planting intentions because they were set up to drill or dry broadcast their seed. A year ago, we were nearly finished planting in south Louisiana in contrast to being 50 percent planted by the end of March this year.

Quite a few farmers decided to switch from dry planting to waterseeding. While that seems simple, it poses several problems. First, the amount of seed used to water-seed is one and one-half to two times the quantity needed for drill seeding. Our Rice Varieties and Management Tips publication explains this in detail, recommending from 60 to 90 pounds per acre for drill seeding and from 90 to 125 pounds per acre for water-seeding. Farmers who intended to drill seed a new variety in short supply might not find enough seed to cover it.

In other cases, some farmers intended to drill then pull internal levees. Wet conditions prevented them from constructing the levees, thus they could not hold the water necessary for water-seeding. In the past, most farmers built levees and installed gates ahead of typical winter rains, allowing them to capture rain water. The expense of having to pump up a field because it is too wet is truly ironic.

Still other farmers had prepared their fields in the fall with the intention of drill seeding into a stale seedbed. In the early days of reduced tillage rice farming (prior to Clearfield technology), stand failure was a common problem when seed were flown into standing water on stale seedbed fields. The problem was and remains obtaining good seed-to-soil contact. I have seen seeds with a two- to threeinch long root suspended in vegetation or simply floating in the water. These seeds seldom survive.

Switching from dry planting to water-seeding also affects fertilizer application and timing and pest management. Herbicide programs in dry-seeded rice are often different from those employed when waterseeding is practiced, especially if water-seeding is done in conjunction with pinpoint flood water management. Only Dermacor is labeled as a seed treatment insecticide for water-seeded rice.

This is all pointing to a later crop than we would like to see. If it gets as hot this summer as it has for the past two, and the crop is delayed, we are going to suffer even more problems with poor seed set and more bacterial panicle blight. Unlike fairy tales, seldom are things “just right” in the real world.


Intermittent flood

Mississippi rice producers have become very efficient with water use over the last couple of decades. Precision land forming has been a most effective tool for improving water conservation. Side-inlet irrigation has been another effective water conservation method for rice.

Even with the above mentioned water conservation methods being utilized, rice producers can still reduce water use with intermittent flooding.

Intermittent flooding initiates the flood as we always have in conventional flooding systems. However, after the flood is established, it is allowed to subside down to mud in the top paddy before the flood is reestablished.

Intermittent flooding allows for an increased potential in rainfall capture when the flood is allowed to subside each time. Also, this system can increase water conservation by reducing over pumping by always keeping the paddies full. The first two weeks of flooding are more critical for nitrogen fertilizer efficiency and weed control. As you move further into the season, it becomes easier to let the flood subside.

This is not a one-size-fits-all flooding program. Intermittent flooding has its best fit on heavy clay soils. These soils have a high water holding capacity level. Therefore, it is hard for them to quickly dry out.

Sandy to silt loam soils could be more of an issue utilizing intermittent flooding. These types of soils tend to dry out quicker and can have higher percolation rates. Also, areas where neck blast continues to be a problem, intermittent flooding would not be recommended.

Employing the use of side-inlet irrigation alone in a straight levee production system would save approximately $13 to $15 per acre over traditional flooding of straight levee rice. With intermittent flooding, another savings of $10 to $25 per acre could be realized due the reduction in pumping cost.

Water conservation in rice begins with side-inlet irrigation. The use of polypipe adds more flexibility in rice water use, such as intermittent flooding.

Adopting water conservation methods will be very difficult without beginning with side-inlet irrigation.


Precious resource

Water and water management in rice production are huge issues in Texas due to the extreme drought last year. We know the value of conserving water and we have adopted many of the techniques, such as precision leveling, polypipe, multiple inlets, vegetation control in inlet canals and ditches, good weed management, early planting, early maturing varieties, frequent and careful inspections of levees and water gates, use of “freeboard” to capture rainwater, shallow flood, avoiding spillage, etc.

Not only Texas farmers, but farmers in all rice-producing states must conserve this precious natural resource. The population of Texas is growing rapidly. The Texas Water Resources Institute estimates the Texas population will increase from 25.4 million to 46.3 million from 2010 to 2060 – an 82 percent increase over 50 years!

Basically, our farmers are competing with urban/suburban communities and industry for water – now and in the future. The drought simply exacerbated the situation and drove home the importance of water conservation and development/exploitation of new water resources. To illustrate the competition for water among rice farmers, urban communities and industry, I contacted the Lower Neches Valley Authority (LNVA), which supplies water for rice grown in Jefferson, Chambers and Liberty Counties. These counties are located east of Houston. Water rates are: $20.00, $65.17 and $81.46/acre-ft for agriculture, municipal and industrial uses, respectively.

This eastern portion of the Texas Rice Belt has received above normal amounts of rainfall during the winter. In fact, at the Beaumont Center, from the start of 2012 to the end of March, 20.81 inches of rain have fallen compared to the historical average of 12.76 inches. So, the LNVA will not restrict water use for area rice farmers for both main and ratoon crops. This “unexpected relief from drought” will provide water for approximately 22,000 acres of rice east of Houston in 2012. However, west and south of Houston is a different story. According to the Lower Colorado River Authority (LCRA), which supplies surface water to the major rice-growing area of Texas, the combined storage of lakes Buchanan and Travis (northwest of Austin) was below 850,000 acre-feet on March 1. This triggered water restrictions for most rice farmers relying on Colorado River water. So, these rice farmers will not receive any water in 2012. In response to this action, some rice farmers are drilling or refurbishing water wells, which is an expensive proposition. Dr. Larry Falconer, Texas Agri- Life Extension Service economist, estimates the total well investment (for one well) is over $275,000!

Another important aspect of water management is water quality. Dr. Garry McCauley, Texas AgriLife Research rice agronomist, conducted a study several years ago and found the sediment load of water entering rice fields was more than that of water exiting fields. In other words, rice fields serve as “lagoons” or “settling ponds” to help purify water. In addition, biotic and abiotic processes in rice fields help breakdown pesticides to minimize on- and off-target contamination – all for the good, making our rice farmers excellent stewards of the environment!

At the recent Rice Technical Working Group meeting in Arkansas, I listened to Dr. Robbie Kröger, Mississippi State University water quality specialist, talk about rice field drainage ditches. His studies show vegetated drainage ditches act as “mini-wetlands” to reduce total inorganic nitrogen loads by 47 percent and total inorganic phosphorous loads by 53 percent. This means less polluted water entering the Gulf of Mexico. Robbie also found low grade weirs built into drainage ditches “create multiple sites for increased sedimentation, nutrient transformation and removal.” Kinks need to be worked out in fine-tuning and implementing this technology, but I believe it is a step in the right direction – better management of the most important natural resource in rice production, WATER!

Drs. Robbie Kröger, Garry McCauley and Larry Falconer co-authored this article with Dr. Mo Way.


Herbicide programs

Careful land grading and seedbed preparation before planting help maintain uniform water depths in rice fields. Ideally, fields are flooded continuously to a depth sufficient to suppress weeds, particularly the grasses and small flower umbrella sedge. However, this works only if the herbicides are effective when applied into the water.

The development of weed resistance to many of the into-the-water herbicides necessitated a change to foliar active herbicides. Foliar herbicides require drainage of the field to achieve good coverage, particularly if small weeds are to be effectively controlled.

Further complicating selection of the proper herbicides are the different water management techniques used by growers. There are four general categories: Continuous flood, Leather’s method, delayed pinpoint flood and drill (dry) seeding. Optimal herbicide programs can vary depending on water management technique.

A continuous flood system enhances herbicide efficacy and maximizes weed control. Sprangletop and barnyardgrass problems are essentially eliminated by the flood. Into-the-water-herbicides are well suited to this system. When late postemergence applications are needed, water is lowered to expose about 70 percent of weed foliage to the herbicide spray, but the fields are never drained.

The Leather’s method uses a planned drain period (three to five days) to improve stand establishment. Foundation herbicides are applied prior to the reflood. Often, cold weather or windy conditions in spring require early field drainage to facilitate rice establishment, precluding the use of into-the-water treatments.

In a delayed pinpoint flood, the field is drained two to three weeks after seeding to expose weeds to improve contact herbicide efficacy. The duration of the drain depends on the method of application, e.g. air or ground. A prolonged drain period can lead to substantial losses of nitrogen fertilizer due to volatilization. These losses begin long before the soil “cracks.” A pinpoint flood system encourages sprangletop and barnyardgrass.

Drill-seeding favors weeds adapted to dryland seedbeds (e.g. sprangletop and barnyardgrass) and is less favorable for aquatic species (e.g. ricefield bulrush) because permanent flood is established about 25 days after seeding. This system offers flexibility for herbicide use when proximity to sensitive crops imposes restrictions on aerial applications.

Work by Dr. Albert Fischer at UC Davis has proven several herbicide combinations to be effective. Below are a few examples. Use of product names does not infer an endorsement by UC.

Erratic control of weeds by a once effective herbicide program may be a harbinger of resistance. Routinely rotate the mode(s) of action used in your weed control program. More weed management research results can be found at the California Rice Research Board Web site: http://www.carrb.com/AnnualRpts.htm.

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