Anhydrous application is beginning in many fields. See stories in this week's CropWatch on anhydrous equipment and applicator safety as well as a trend in anhydrous use. (Photo by Brett Hampton)

April 9, 2004

Monitor shows disparity in soil moisture levels:
east recovering, but the west looks for snowmelt

Figure 1. Estimated soil moisture in inches available in the top five feet of the profile as of April 2, based on accumulated precipitation at each reporting cooperative weather station. Accumulated totals were multiplied by an efficiency factor of 0.65 to provide a rough estimate of how much available moisture may be in the soil profile. (Map developed by Al Dutcher, State Meteorologist, High Plains Climate Center.) Figure 2. Difference between 2004 estimated available soil moisture (Figure 1) and normal soil moisture levels in inches, based on 1971-2000 precipitation normals multiplied by an efficiency factor of 0.65. (Map developed by Al Dutcher, State Meteorologist, High Plains Climate Center.)

We have attempted to develop a relationship between the current available moisture at each of the monitoring sites and precipitation since October 1, 2003. The average effective rate of precipitation for these sites has been 65%. This means that for each inch of moisture received since October 1, about 0.65 inch has been captured in the profile. Please note that these sites are under grass and fields dedicated to production agriculture may have higher or lower infiltration rates.

Figure 1 represents the estimated soil moisture available in the top five feet of the profile as of April 2. This figure was developed by using the accumulated precipitation at each reporting weather station. The accumulated totals were multiplied by an efficiency factor of 0.65 to provide a rough estimate of how much available moisture may be in the profile.

Figure 2 represents the difference between the available soil moisture illustrated in Figure 1 and an average of climatological baseline normals from 1971-2000. In simple terms, Figure 2 is the difference between Figure 1 and the 1971-2000 precipitation normals multiplied by a factor of 0.65. The HPRCC soil monitoring sites have not existed long enough to develop viable soil moisture normals, so this is our best attempt to quantify how our current soil moisture status compares to some type of historical baseline.

These soil moisture figures will be updated weekly in CropWatch through late May. It’s important to remember that these are estimates based on past infiltration relationships. In addition, these files will not reflect crop water use extraction and should only be used to gauge soil moisture in an area that has not yet been prepared for the 2004 production season.

During April, soils across eastern Nebraska should be gaining about 0.50 inch of available soil moisture per week, while western Nebraska should be adding 0.40 inch a week. During May, eastern Nebraska soils should gain an average of 0.75 inch per week and western Nebraska should gain 0.50-0.60 inch a week.

If precipitation falls below normal any week, Figure 2 will show a further decrease from the previous week in areas with a soil moisture deficit, along with a reduction in areas that show a surplus. Conversely, above normal precipitation will either reduce soil moisture deficits from the previous week or add to areas with a surplus.

Soybeans vs dry beans in western Nebraska

Weed control. With the development of Roundup Ready soybeans and the decreased price of glyphosate, soybeans may offer an advantage in weed management. With soybeans, usually the producer achieves a more profitable crop by using at least a two-thirds or higher rate of a preplant or preemergence herbicide rather than totally relying on a postemergence weed management program.

Timing is critical when weed control depends on post-emergence applications. If an application is late, weeds may be controlled, but yields will have already suffered. A preplant or preemergence treatment will widen the period for post applications.

Harvest. Another advantage of planting soybeans is being able to direct harvest. Flex platforms which follow the contour of the ground have reduced soybean losses in the field.

Growing season. One of the disadvantages to planting soybeans in western Nebraska is that they push the growing season. This is especially true in high elevation areas where early fall frost can occur before soybeans mature. While helpful, early planting can only be so early. At some western locations, a late spring frost is likely to nip beans planted prior to May 20.

Nitrogen. Both crops reduce the amount of nitrogen needed for the next crop. The nitrogen produced by either crop is not available early enough for a following winter wheat crop but is available for succeeding crops or late spring planted crops. Also, most crops do benefit from following either crops.

Residue. A disadvantage of dry beans is that after harvest, little residue is present, which makes the soil subject to erosion. The plus side of dry beans is that they are usually harvested earlier and it is possible to seed winter wheat sooner than following soybeans.

Long-term picture. If you’ve become a little discouraged with dry beans, don’t write them off too quickly. Usually the grower has been compensated over several years for the extra management and expense of producing this crop.

Summary. Investigate both crops thoroughly before making a decision. Also check with crop insurance and Farm Service Agency programs.

Army cutworm

There have been some reports of chemical salesmen recommending higher rates than necessary for cutworm control, suggesting that the extra insecticide will give extended residual to help control the alfalfa weevil when it appears. While there may be some effect on the alfalfa weevil adults entering the field to lay eggs, or some activity on newly hatched larvae in southern and western Nebraska, there is no way to scout this early for alfalfa weevils in most parts of the state to make an informed decision.

Our recommendation is to deal with the army cutworm now, if necessary, and wait to see about the weevils. The threshold for army cutworms in alfalfa is two or more per square foot on seedling alfalfa and four or more per square foot for established stands, or two to four per square foot in wheat, depending on stress and moisture conditions.

In alfalfa, if the fields appear to be greening up normally, army cutworm will not be a problem. Starting next week, army cutworms will begin to cease feeding as they mature, and damage will taper off. Treatment after the April 12 or so will have much less return compared to this week. See the April 2 CropWatch for recommended insecticides for army cutworms.

For optimum front-wheel-assist performance, start with weight distribution. About 40% of the static tractor weight should be on the front wheels and 60% on the rear. In contrast, two-wheel-drive tractors should have about 25% of their weight on the front and 75% on the rear. Most tractor manufacturers recommend the same total tractor weight per horsepower for front-wheel-assist and two-wheel-drive tractors. This can mean up to 25% less rear axle weight with front-wheel-assist, resulting in less compaction. (Compaction is a function of axle weight.) Also, make sure the rear tires follow in the tracks firmed by the front tires, again reducing compaction up to 80% compared to multiple wheel tracks.

Always use single rear wheels on front-wheel-assist tractors. Using duals cuts traction, increases slip, and increases rolling resistance because the outer dual wheels “lifts” the inner tires from the tracks left by the front drive tires. Producers who think they increased pull because of duals on a front-wheel-assist tractor did so because they added weight (of the duals) to the rear of the tractor. They probably would have increased pull even more by adding the same amount of weight distributed to both the front and rear of the tractor to maintain the proper 40/60 ratio.

In the field, use the front-wheel-assist all the time. Ballasting for front-wheel drive and not using it wastes power and makes steering difficult. Ballasting for two-wheel drive and only engaging the front-wheel drive in tough spots doesn’t leave enough front weight for traction, contributing to “wheel hop”. Tractors with powered front wheels have less rolling resistance because the drive wheels continually climb out of their tracks. In addition, the rear drive wheels have less rolling resistance and can pull 28% to 50% more than the front wheels because they are running in already firmed tracks in the soil. Because of these firm tracks, a properly ballasted front-wheel-assist tractor will have 3% to 7% higher tractive efficiency than a two-wheel-drive tractor of the same horsepower and weight. If duals are added to the rear wheels, as with four-wheel-drive tractors, also add duals to the front wheels to firm the soil for the rear duals.

For optimum field performance, always use the recommended tires and inflation pressures on the front and rear tires of a front-wheel-assist tractor. Improper tire size or inflation can change the rolling radius of the tire, reducing the tractive efficiency, and may damage the power train or cause excessive tire wear. Consult the owner’s manual for these and other recommendations to get the most from your front-wheel-assist tractor.

Producers often add duals or weights to increase the pull of their tractor. But traction does not always increase with duals. In fact, single tires can pull as much as duals in firm soil when both are weighted equally. The increased traction from duals often comes from the added weight of the duals. However, any added weight adds to compaction. Another disadvantage of duals is that the weight and increased rolling resistance requires extra power to move the tractor itself through the field, reducing performance compared to single tires.

To make more effective use of the tractor’s power, it’s usually better to reduce draft (implement width or operating depth) and increase operating speed since power is a function of both. The reduced draft requires less weight on the tractor to develop the needed pull, further reducing compaction.

Running duals can increase a tractor’s load-carrying capacity if single tires cannot support the load safely. But duals can create a “pinch row” effect on the soil between the tires and compaction is increased because four sidewalls are contacting the soil.

Rather than using duals, a producer may be better off by switching to larger diameter tires or tires with a higher star (or ply) rating to carry the load and adjusting the inflation pressure. However, any added load increases the potential for compaction. A better alternative may be lift assist wheels on mounted equipment or switching to pull-type equipment so that more axles are available to carry the load. In addition to reducing compaction, not as much tractor front end weight will be needed for stability. Usually, lift assist wheels are cheaper than duals and are more effective at handling the load safely, especially during transport.

“Anhydrous” means without water. Consequently, when NH₃ contacts water, it rapidly combines with the moisture and forms ammonium hydroxide. When it is injected into the soil, the liquid ammonia expands into a gas and combines with soil moisture. Similarly, the liquid or gas that contacts body tissue –– especially the eyes, skin and respiratory tract –– will remove the water and cause dehydration, cell destruction and severe chemical burns.

Producers can protect themselves by following these guidelines:

Wear properly fitted unvented goggles or a face shield, lose-fitting rubber gloves and a heavy-duty long-sleeved shirt. Regular glasses will not provide adequate protection. Never wear contact lenses when working with NH₃. Anhydrous ammonia can get under the lenses and cause permanent eye damage before the lenses can be removed and eyes flushed with water.

Work upwind of machinery, the hose-end valve, bleeder valve, coupler or plugged applicator tubes and plan an escape route.

Keep children away from the equipment. Federal law requires that children younger than 16 not handle, transport or transfer NH₃.

Water, water, water is the only first aid for anhydrous ammonia. Regulations require that all farm vehicles used for NH₃ carry a container filled with at least five gallons of water which is readily available for flushing eyes and skin. Change the water daily to ensure a clean supply. Safety specialists recommend keeping a second five-gallon container of water on the tractor. A pencil size stream of water will consume five gallons of water in 7.5 minutes. The extra five gallons in the tractor provides another source of water for first aid in case the tractor operator is unable to reach the water container on the nurse tank.

Carry a six- to eight-ounce water-filled plastic eye wash bottle in a shirt pocket. It provides an immediate supply of water in case of an accident. The eye wash bottle allows for some ammonia to be washed out of the victim’s eyes in the first few seconds.

When someone is exposed to NH₃, move him or her to a safe place and immediately flush the exposed area with water and continue flushing it for at least 15 minutes. Remove contaminated clothing as soon as it is thawed. Remember, the sub-zero temperature (-28° F) of NH₃ can freeze clothing to the skin. Removing clothing before thawing with rinse water can cause extensive skin damage. Contact a doctor or emergency medical services immediately after emergency first aid treatment.

Even if small amounts of NH₃ enter the eyes, irrigate them immediately with water for 15 minutes or more. Hold the eyelids open during irrigation to ensure water contacts all parts of the eye. Immediate first aid is important to avoid partial or total loss of vision.

Anhydrous ammonia vapors are easily detected because of their pungent odor, even in low concentrations. Inhalation of NH₃ can irritate the respiratory tract and lungs. At high concentrations, NH₃ combined with the moisture in the lungs, may damage the alveoli (lung lining) and reduce the ability to transfer oxygen to the bloodstream.

When a person has inhaled ammonia, move the victim to a safe area. Exposures to low concentrations of NH₃ for a short period of time may not require treatment. Exposure to higher concentrations may cause convulsive coughing and respiratory spasms. Provide rescue breathing if victims are not breathing and CPR if they have no pulse. Obtain medical help as soon as possible.

Two weevils can be causing damage, but usually the most important of the two is the alfalfa weevil. Clover leaf weevils occasionally are problems; however, they are very vulnerable to fungus disease and haven’t been pests since the late 80s and early 90s when spring rains were rare. They may be making a comeback in drought areas where moisture has been limited.

Both weevils feed on first cutting alfalfa as larvae, and on regrowth of the first cutting as adults. While research conducted in northeast Nebraska indicates that clover leaf weevil larvae feeding does not cause yield reduction to first cutting alfalfa, alfalfa weevil feeding can cause severe losses to yield and quality of the first cutting.

The warning signals are chemical compounds called green leafy volatiles (GLV). Shortly after coming under attack from pests, corn plants send these volatiles into the air to draw support from the pest's natural enemies. The volatiles, which smell like cut grass, attract caterpillar predators and parasitoids. When the researchers exposed undamaged corn seedlings to GLV from damaged plants, the seedlings' chemical defenses increased. But an even stronger defensive reaction was triggered when seedlings were exposed to the volatiles, purposely damaged and then treated with a beet armyworm caterpillar substance to imitate insect attack.

Plants used as an experimental control were damaged, but never exposed to GLV. They did not react as strongly, which suggests that the volatile signals help prepare the plants' defensive reaction. Different, night-time volatiles also stimulated a defensive reaction in neighboring plants. Plants that were sensitized to GLV first and then damaged--but not exposed to the caterpillar substance--did not react as strongly as they would have if they had been exposed to the caterpillar substance.

Former ARS researcher James H. Tumlinson led the study before retiring from the agency. He and his colleagues at ARS, Pennsylvania State University and the University of Florida reported their findings in a recent issue of the Proceedings of the National Academy of Sciences. Tumlinson, a chemist, is now a visiting Penn State professor at the ARS Center for Medical, Agricultural and Veterinary Entomology in Gainesville, Fla.

Jim Core
ARS Writer

USDA researcher and plant geneticist Cheryl Baker infests greenhouse colonies with the newly found biotype of Russian wheat aphid. These colonies will be used to infest plants that will be screened for resistance to this aphid. (USDA ARS photo)

In Stillwater, entomologist James Webster and geneticists Cheryl Baker and Dolores Mornhinweg reacted to the discovery of the first aphid biotype by screening 30,000 wheat and 24,000 barley germplasm accessions for resistance traits for incorporation into new crop lines. Most of that germplasm was obtained from the Aberdeen unit's National Small Grains Collection. That work led to identification of more than 300 resistant wheat germplasm lines and 40 promising barley germplasm lines.

Now, the new biotype has led Baker and Mornhinweg to re-examine breeding lines they developed during the first crisis. Mornhinweg tested about one-third of the barley lines found to be resistant to the original aphid and discovered they were resistant to the new type. Also, four breeding lines of winter barley and three feed barleys set to be released within the next few years show resistance to both aphid biotypes.

Baker has found strong candidates among the advanced wheat lines, including a promising one derived from a wheat-rye line she received from a South African scientist.

Geneticist Mitch McGrath (left) discusses differences between smooth-root and traditional sugar beets with technician Tim Duckert. (USDA ARS photo)

The ARS group is one of just a few in the world and the only one in the United States working on the sugar beet genome. The group includes J. Mitchell McGrath, who heads a research team at the ARS Sugar Beet and Bean Research Unit at East Lansing, Mich.; plant pathologist John Weiland at ARS' Sugar Beet and Potato Research Unit at Fargo, N.D.; plant geneticist Leonard Panella of ARS' Sugar Beet Research Unit at Fort Collins, Colo.; and Robert Lewellen, plant geneticist at ARS' Crop Improvement and Protection Research Unit at Salinas, Calif.

Already, McGrath's group and two independent groups in Germany have deposited more than 20,000 ESTs (expressed sequence tags) into the National Center for Biotechnology Information's GenBank site. These tags identify probably one-third to one-half of the 30,000 genes thought to make up the functional part of the sugar beet genome.

McGrath worked with Weiland and a contract firm to package a BAC (bacterial artificial chromosomes) "library." This type of "library" uses safe strains of bacteria to store sugar beet DNA. These sequences are then either screened with genetic markers, or compared with sequences of known genes, to connect them to possible traits. Each clone in the library of 38,400 cloned bacteria stores a different DNA sequence from the sugar beet's genome. Panella and Lewellen also collaborated on the library.

Under a Memorandum of Understanding between the U.S. Department of Agriculture and the BSDF, ARS is charged with developing basic germplasm lines and releasing them to the foundation, for distribution to BSDF members.

Scott Brady, Extension Educator in Greeley, Howard, Sherman and Valley counties: Field preparation and fertilizer applications are underway. If the weather cooperates, corn planting will probably begin next week. Some alfalfa is being treated for cutworms. We’re finishing up calving and spraying some pastures. USDA’s Nebraska Agricultural Statistics Service reported this week that wheat condition rated 11% very poor, 23% poor, 37% fair, 26% good, and 3% excellent, near last year and the average. Fields had begun to joint in some southern and eastern counties.

Randy Pryor, Extension Educator in Saline County: The early spring weather has prompted preplant anhydrous and phosphorous fertilizer applications, with some early corn planting to follow. This week I observed one farmer disking up a level, weed-free, soybean stubble field that would have made a beautiful seedbed for no-till corn. Change is often difficult, but this change can improve a farm’s bottom line. The winter wheat crop is good to excellent, and we’ve got an excellent window for fertilizer and weed control applications.

Tom Holman, Extension Educator in Scotts Bluff and Morrill counties: Producers are chopping stalks and turning them under in preparation for planting; probably 10-20% of the county’s sugarbeet crop has been planted. Following several years of drought and low prices, more and more farmers here are looking at nontraditional crops such as annual forages and irrigated grass. There is a strong producer movement toward moisture preservation through minimum or no-till.