Polypipe initiates water conservation.
Water conservation is a mindset that will soon have to be adopted in the Mississippi Delta. With a declining water aquifer, water conservation could soon be mandated if not adopted soon. Mississippi rice producers, over time, have become more efficient with water use. Most of the efficiency has come from precision land forming and the use of polypipe for rice irrigation. Even with this technology, rice producers need to think about tightening the belt another notch.
Yazoo Mississippi Delta Joint Water Management District (YMD) has collected data on water use in rice using various irrigation practices. Precision land forming (straight levee rice) results in an annual water savings in six inches of water over contour levee rice (44.4 inches of water). The use of side-inlet irrigation, with straight levee rice production, results in saving another 7.2 inches of water over straight levee rice (38.4 inches of water). Zero-grade rice production uses approximately 20 inches of water, which is less water than any other irrigation practice in rice. Zero-grade rice production has advantages in a rice monoculture system; however, problems exist with rotation crops such as soybeans.
Based on current estimates, the use of side-inlet irrigation in straight levee production would save approximately $13 to $15/A over traditional flooding straight levee rice. With side-inlet, additional savings can be seen when a pumping cycle (turning the well on every five to seven days) can be established over keeping the paddies continually full. Meaning that if a rainfall event occurred between pumping cycles, that water could be captured since the flood was allowed to subside (decline two to four inches below the gate height).
These are ideas that rice producers need to think about to prevent further regulations imposed on water use in Mississippi. Polypipe is the most valuable tool to help initiate water conservation. Without it, adopting water conservation methods will be very difficult.
Control the flood to help avoid blast
Water is key for a successful rice crop, and this became evident during the drought we experienced in 2011. Water management is important not only to meet the needs of the rice plant (rice is not a drought-tolerant crop), but it also impacts other management practices such as weed control, fertilizer efficiency and disease severity.
Ideally, farmers need to be able to establish the flood in two to three days in dry-seeded rice. Realistically, the time required may range from two days to 15 days. When the time is delayed to more than two days, nitrogen is lost by ammonia volatilization.
Flood management is a critical step in managing rice blast disease. Dr. Fleet Lee demonstrated that a deep flood after mid-season can greatly reduce the incidence and severity of rice blast, even in blast-susceptible varieties. The inability to maintain a constant flood when growing a blast-susceptible variety increases the risk of blast enormously.
When growing blast-susceptible varieties, a shallow but steady flood should be maintained until mid-season. After mid-season, the flood depth should be brought to a depth of four to six inches and maintained until maturity. Fields that must be drained for straighthead are often the most severely impacted. Blast becomes established while the field has been drained. If weather and water capacity limit the ability to re-establish the flood, blast can spread throughout the field and become severe.
While the majority of the rice produced in the Mid-South is flood irrigated, there has been increased interest in Arkansas in furrow-irrigated rice (or “row-watered rice”) and sprinkler-irrigated rice with center pivots. In the right situations, furrow-irrigated rice can provide some significant benefits. Fields on hillsides where levees are so close that there is very little “paddy rice” are most effectively converted to furrow-irrigated rice.
However, there are certain risks with this system that should be considered. The biggest issues with furrow-irrigated rice are disease risks and unknowns concerning other management. In research trials, yields have been reduced compared to flood-irrigated rice. A blast-resistant variety is needed to reduce the risk from this disease. Hybrid rice has been an effective choice in these situations.
Residual herbicides have certainly made weeds easier to manage in this system but are still not fool-proof. Weeds not commonly a problem in rice become a serious problem due to the lack of a flood for control. For example, Palmer amaranth (pigweed) is normally controlled by the flood, but in furrow-irrigated rice can be a challenge. Current residual herbicides labeled for rice do not provide effective residual control of pigweeds. Propanil and Aim burn the vegetation but normally do not give a complete kill. Repeat applications may be needed in fields with heavy pigweed pressure.
Because of the upland situation, rice produced under a center pivot faces many of the same challenges as furrow-irrigated rice. There has been some success reported in the Mid-South using this system. However, wide-spread adoption of either of these upland production systems will place extreme pressure on the resistance to rice blast disease. Resistant varieties, such as current hybrid rice, are the most successful choices under Arkansas conditions. However, it is possible, and actually likely, that the blast fungus can adapt and overcome these resistance genes.
Test correctly for salty water
While I have not had any calls from Louisiana about salt water this year, 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, supplies of fresh surface water are likely to become critical in some areas. The same thing may happen when using wells in areas where the aquifer has dropped or where borderline salt problems already exist.
A great deal was learned about salt problems following Hurricanes Rita and Ike. Vermilion Parish rice acreage has never returned to the 1980s and early 1990s levels when it was often the No. 1 rice parish in terms of acreage devoted to rice production. At the time, we had little information on salt in soil. Researchers quickly put together studies to help farmers decide whether they would be able to plant in the spring following the hurricanes. A level of 750 parts per million (ppm) was established as the maximum safe level. It’s a conservative number that has, to this point, proven itself in field situations.
On the rice Web page (www.lsuagcenter.com/3n/crops_live-stock/crops/rice/Publications/) is an old publication addressing safe salt levels in irrigation water. This is a separate issue from salt in the soil; however, the two are interrelated. In the guide to using salt water in rice are several levels of salt in water that are considered “safe levels,” depending on growth stage of the plant at the time water is to be applied. One important assumption regarding these levels is that the soil is free of salt to begin with and that salty water will not be added repeatedly. If the soil is already salty or if more than one irrigation is planned, the published numbers are no longer valid.
Most growers use inexpensive meters to estimate the amount of salt in their water. These meters are electrical conductivity meters. They function on the basis that salty water conducts electricity easier than fresh water. A major limitation of these meters is that they can’t identify the type of salt present. In a few cases, high conductivity readings have been from the presence of high levels of calcium rather than sodium. High calcium levels are not a problem, but high levels of sodium are. If a high conductivity reading is obtained from a well, a complete water analysis should follow before condemning the well. High salt levels in surface water are most often from sodium because they usually occur when coastal water moves inland.
A good rule of thumb to follow is “When in doubt, don’t.” Repeated use of salty water not only can affect this year’s crop but can cause long-term problems in the soil.
Dihydrogen oxide and other stories
Water management is a season-long consideration, including the water already in the fields from the spring rains. So far, the spring of 2011 is a wet one in California. Rains have persisted throughout March. Given that it takes three to four weeks for the heavy clay soils of the Sacramento Valley to dry enough for cultivation, any additional rains will delay planting.
In wet springs, there is always the temptation to rush planting even if the soil has not adequately dried. It is important to remember that the young rice seedling depends upon the dissolved oxygen at the soil/water interface. Seedlings frequently struggle when planting is “shot-gunned” into wet soil. When possible, dry the soil before flooding to plant to improve seedling vigor. Waiting a day or two can actually accelerate stand establishment.
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 not only get a head start on the rice but there can be a range of weed development from the top to the bottom of the field, which can compromise herbicide efficacy. Scout the uppermost checks for early infestations of tadpole shrimp. Also, keep in mind that in areas with cold irrigation water, the weeds (and rice plants) in the intake check may lag behind in development compared to rest of the field. In extreme circumstances, the timing for optimal weed control can be several days later in the cold water checks.
When putting together your weed management program, don’t forget to include dihydrogen oxide (water). Ever since California transitioned to a water-seeded system in the 1930s, water has been a key ingredient for effective weed control. It is old, but still valuable chemistry. Water suppresses watergrass growth and can improve the efficacy of herbicides. If you must drain, reflood as soon as possible. This reduces the chances of a second flush of weeds and prevents the loss of nitrogen fertilizer through volatilization.
Research conducted by Albert Fischer (UCD) showed that short drain periods (e.g. pin-point flood) shift weed population characteristics. Periods of water drain favor grass weeds. Bruce Lindquist (UCD) demonstrated that a drained field loses about two pounds of nitrogen per day. The loss begins when the soil is still saturated with little or no standing water. The “starter” fertilizer applied to the surface is the most susceptible to loss during drain periods.
As always, it is a good practice to raise the water depth to protect the developing pollen from low temperature sterility. The developing flower is about two inches above the soil line. The sensitive stage of development occurs about seven days after panicle initiation. The critical temperature is 55 degrees F for four hours or more. The duration of the sensitivity persists for about 7 – 10 days in a given field due to differences in panicle maturation between plants. There is no need to keep the water deep beyond this stage of development. Pollen sensitivity occurs when the collar of the flag lead is aligned with the collar of the previous.
Refer to page 9 at the following link for an illustration: http://www.plantsciences.ucdavis.edu/uccerice/rice_production_workshop/36231.pdf.
Good stewardship of this limited resource – water – improves profitability and preserves the rice industry’s reputation of being an environmentally responsible farming system.
Water use efficiency
Water is becoming more and more limiting and precious to Texas rice farmers and our urban/suburban neighbors. Basically, water for rice production is facing stiff competition from city dwellers. The Texas Rice Belt lies on the Upper Gulf Coast of Texas. A number of large rivers, whose headwaters are in north Texas, cut across this region and provide water for agriculture, industry and municipalities. These rivers include the Sabine, Neches, Trinity, Brazos, San Bernard, Colorado and Navidad.
Dr. Garry McCauley estimates about 75 percent of Texas rice acreage is irrigated with surface water. For instance, the Colorado River, which runs through the heart of the Texas Rice Belt, will supply water for about 67,000 rice acres in 2011 (data provided by Ron Gertson, rice farmer and member of the Colorado Water Issues Committee). This represents about one-third of the total Texas rice acres projected for this year.
Texas’ population increased 20.6 percent from 2000 to 2010. Houston is the fourth largest city in the United States; San Antonio is the seventh largest; Dallas is the ninth largest; Austin is the fifteenth largest; Fort Worth is the seventeenth largest; and Corpus Christi had a population of about 290,000 in 2009. These Texas cities now or may in the future compete for our rice water.
According to McCauley, our rice farmers now use much less water on a per acre-foot basis than in the past. Rice farmers have become much more efficient in water usage thanks to research, development and adoption.
Garry says the average rice water usage in Texas now is less than three acre-feet annually. Dr. Larry Falconer estimates main crop water usage at 2.75 acre-feet for 2011. In the past, Texas farmers routinely used four to six acre-feet to produce a rice crop. This trend is widespread across U.S. agriculture. Since 1980, irrigation water withdrawals in the United States have stabilized, in part due to advances in irrigation efficiency; however, urban populations and water usage have continued to expand, resulting in dramatic increases in overall water withdrawals.
Last year, rice farmers who withdrew water from the Colorado River faced the real possibility of not being able to produce a ratoon crop because of a water shortage. Basically, the drought of 2009 depleted water levels in the highland lakes northwest of Austin. Once these levels reach a critical lower threshold, water for agriculture is restricted. If the drought had continued, no water would have been released for ratoon crop production. Fortunately, rainfall was sufficient during the fall and winter of 2009/2010 to replenish these lakes, which averted a disaster.
About 50-60 percent of Texas rice acreage is ratooned. Many of our farmers now produce ratoon crops equal to one-third to one-half of main crop yields. In addition, last year panicle blight and untimely rainfall during flowering, on average, reduced main crop yields 15-20 percent. However, the ratoon crop was good, which made up somewhat for poor main crop yields. So, the ratoon crop was even more important to our producers last year than in past years.
We can’t do much about droughts, but we can surely continue improving water-use efficiency through research, development and adoption. I believe our rice industry is a model for water-use efficiency. Our urban neighbors should learn from our progress.