Tuesday, December 3, 2013

Weeds Welcome Global Warming

As temperature and carbon dioxide levels in the atmosphere increase, growers may see things pop up in their fields that they haven't seen before. Unfortunately, they won't all be good.

In a session on climate, carbon dioxide and invasive weed species at the University of Illinois AGMasters Conference, USDA-ARS crop systems specialist Lewis Ziska discussed how rising carbon dioxide levels and rising temperatures may cause invasive weed populations to change.

"Carbon dioxide provides the raw material needed for plants to grow, and as it increases, plant growth will be stimulated. Carbon dioxide is not a smart molecule -- it can't distinguish between crops and weeds. So with increased growth of crops comes increased growth of weeds as well."

Ziska is studying how rising carbon dioxide and warmer temperatures alter the establishment and success of invasive and noxious weed species such as kudzu and Canada thistle. These weeds can result in widespread environmental or species degradation.

"In general, as temperature and carbon dioxide levels change, weeds may be more likely to adapt to these changes given their greater genetic variability relative to crops."

And as winter temperatures warm, kudzu, often referred to as "the vine that ate the South," is migrating northward. This could become problematic for the Midwest because kudzu is a carrier for Asian Soybean Rust and can serve as an alternative host for this pathogen.

On the positive side, Ziska said plant breeders can start selecting among crop lines for a greater yield response to carbon dioxide.

Source: Lewis Ziska, 301-504-6639

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Photo: Kudzo Vine

Monday, October 28, 2013

Enough with the Potassium, Already!

Since the chemical age of agriculture that began in the 1960s, potassium chloride (KCl) - a common salt known as potash - has been widely used as a major fertilizer in the Corn Belt.

Now, University of Illinois soil scientists are raising serious concerns with agriculture's 50-year potassium habit with research showing that testing soils for potassium is of no value for predicting its availability and that KCl fertilization seldom pays.

The findings came from a field study that involved four years of biweekly sampling for K testing with or without air-drying. Test values fluctuated drastically, did not differentiate soil K buildup from depletion, and increased even in the complete absence of K fertilization.

Explaining the increase, researcher Saeed Khan pointed out that for a 200-bushel corn crop, "about 46 pounds of potassium is removed in the grain, whereas the residues return 180 pounds of potassium to the soil—three times more than the next corn crop needs and all readily available."

Khan emphasized the overwhelming abundance of soil potassium, noting that soil test levels have increased over time where corn has been grown continuously. "In 1955 the K test was 216 pounds per acre for the check plot where no potassium has ever been added. In 2005, it was 360."

A similar trend has been seen throughout the world in numerous studies with soils under grain production.

KCl fertilization has long been promoted as a prerequisite for high nutritional value for food and feed. Yet, researchers have found that the qualitative effects were predominantly detrimental, based on a survey of more than 1,400 field trials reported in the scientific literature.

"Potassium depresses calcium and magnesium, which are beneficial minerals for any living system. This can lead to grass tetany or milk fever in livestock, but the problems don't stop there," Khan pointed out.

"Low-calcium diets can also trigger human diseases such as osteoporosis, rickets, and colon cancer. Another major health concern arises from the chloride in KCl, which mobilizes cadmium in the soil and promotes accumulation of this heavy metal in potato and cereal grain. This contaminates many common foods we eat—bread, potatoes, potato chips, French fries—and some we drink, such as beer. I'm reminded of a recent clinical study that links cadmium intake to an increased risk of breast cancer."

The Illinois researchers see no value in soil testing for exchangeable potassium and instead recommend that producers periodically carry out their own strip trials to evaluate whether potassium fertilization is needed. Based on published research cited in their paper, they prefer the use of potassium sulfate, not KCl.

Sources: University of Illinois College of Agricultural, Consumer and Environmental Sciences;
"The potassium paradox: Implications for soil fertility, crop production and human health" by Saeed Khan, Richard Mulvaney, and Timothy Ellsworth posted October 10, 2013 by Renewable Agriculture and Food Systems.

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Artwork: 1909 Potash Print Ad

Monday, October 21, 2013

Waterhemp Becoming a Superweed

Studying the first known case of waterhemp with resistance to HPPD-inhibiting herbicides such as Callisto, weed science researchers at the University of Illinois have identified two unique mechanisms in the plant that have allowed the weed to “get around” these herbicides.

“Waterhemp is very diverse, which you can see in the field. There are red plants, green plants, tall, short, bushy—basically a germplasm pool. If you  keep spraying the same herbicide over and over, eventually you’re going to find that rare plant that can resist it,” said Dean Riechers, a U of I Professor of weed physiology,

What the U of I researchers find alarming is that waterhemp resisted the herbicide in much the same way that corn naturally resists HPPD-inhibiting herbicides.

“It mimics corn but also mimics the super bacteria that are resistant to all the antibiotics out there. Weeds are kind of like bacteria in that respect; at least this population is. Whatever active herbicide we throw on it, with the exception of glyphosate, it doesn’t work anymore,” Riechers said.

The study was prompted in 2009 when a continuous seed corn grower from central Illinois realized the HPPD-inhibiting herbicides he was using were no longer killing waterhemp plants, which by then had grown into a mat of weeds across the field.

“It became obvious to the grower that something was wrong, but it probably started years before that,” Riechers said, adding that the grower had been planting continuous seed corn every year, using HPPD-inhibiting herbicides for at least eight years in a row.

“Mesotrione and atrazine are normally two very good herbicides that are safe on corn but still kill waterhemp,” Riechers said.

Although the 2009 incident was the first to document this type of resistance, Riechers said four or five other locations in the Midwest have since reported similar occurrences.

“It doesn’t appear to be isolated because it looks like there are other resistant populations coming up,” Riechers said. “The concerning thing is that some of these fields actually did have corn and soybean rotations. They weren’t just growing corn, they were rotating, which is what you’re supposed to do. But it still became HPPD resistant, and we’re not sure how that happened.”

Rong Ma, one of the researchers on the study, said growers should consider not using the same herbicide mode of action repeatedly. “For example, don’t use HPPD-inhibiting herbicides alone for several years in a row because it is then easier for weeds to develop resistance," she said

“Growers could also use tillage because there’s no resistance to tillage,” Riechers pointed out. “Farmers use no-till systems, often plant in narrow rows, and for the most part have gotten away from tillage for weed management. We have aided waterhemp in becoming a problem by not using tillage, using the same chemical over and over, and by not rotating crops.”

Source: Dean Riechers University of Illlinois, tel:+1 217-333-9655

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Artwork: Waterhemp

Monday, April 29, 2013

Split Nitrogen Applications for Better Wheat Yield

Experts in soil chemistry at Montana State University caution that applying all the nitrogen fertilizer required for wheat at one time can be risky.

According to MSU Extension, in irrigated systems, too much nitrogen early in the growing season can produce excess tillers, lead to lodging, and reduce yields. In dryland systems, nitrogen fertilizer may not get fully used for plant growth, especially in dry years.

In both dryland and irrigated systems, large, one-time applications have a high chance to be lost to groundwater from leaching or to the air as a gas. This is a financial loss to the producer and potentially detrimental to water and air quality.

Applying pre-plant nitrogen levels based on conservative yield goals is an alternative, especially in dry years. This early nitrogen can be supplemented with mid-to late-season nitrogen to increase grain yield and protein if production potential increases during the season.

By splitting nitrogen application, a producer can better match nitrogen rates to estimated yield potentials based on precipitation to date. If the weather is wet, then fertilizer amount and timing decisions should be based on whether the goal is a yield or protein increase. If the weather has been dry, then a second application may not be advisable.

Timing of in-season nitrogen application should be based on plant growth stage rather than a particular date. In dryland production, additional nitrogen for yield should be applied by early- to mid-tillering, to ensure yield is not hurt. This is particularly important with foliar application for spring wheat. By the time spring wheat approaches the boot stage, weather conditions are such that leaf burn becomes a risk sufficient to hurt yields. Because only about 10 percent of foliar applied nitrogen is taken up by leaves, it is important to follow application with at least half-inch of water to incorporate the nitrogen into the soil.

Incorporation is important for soil-applied nitrogen as well, which is possible in irrigated systems, and sometimes doubtful in dryland systems.

Yield from irrigated fields may increase with nitrogen applied as late as flowering. Although yield may improve with additional nitrogen applied at heading, nitrogen applied this late in the growing season generally cannot compensate for the yield deficit due to early under-fertilization.

Leaf burn increases as the nitrogen rate increases. The maximum suggested rate is 30 pounds nitrogen per acre to minimize yield reduction due to leaf burn. Liquid urea tends to produce less leaf burn than urea-ammonium nitrate (UAN) and therefore can benefit yield more. Leaf damage increases with the inclusion of sulfur, the addition of Agrotain® to urea, or the addition of a surfactant to UAN solution with herbicide when nitrogen rate is greater than 20 pounds nitrogen per acre.

Using streamer bars to minimize direct leaf contact during application can substantially decrease leaf burn.

Late season nitrogen to increase protein is ideally applied at flowering. However, the ability to incorporate with rain or irrigation is more important than the exact timing at flowering.

Leaf burn increases the later that foliar nitrogen is applied. Up to 40 percent flag leaf burn from foliar nitrogen applied around flowering may increase protein, but it can also decrease yields. If there is the risk of scab, do not irrigate within five days of flowering.

The decision to apply late-season nitrogen to increase protein depends on: 1) whether it can be applied without substantially damaging the crop; and 2) if the expected protein response and discount are sufficiently high to justify the cost of fertilizer and application.

Clain Jones, Extension soil fertility specialist.
"Practices to Increase Wheat Grain Protein"
Montana State University Extension bulletin

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Saturday, February 23, 2013

Wood Chips Trap Nitrogen Runoff

Trenches filled with wood chips can trap excess nitrogen and significantly stem nitrate flow from crop fields into the surrounding watershed, according to Agricultural Research Service studies.

Nitrates that leach out from Midwestern crop fields are channeled via underground tile drains, constructed by early settlers to drain soggy prairies, into nearby surface waterways. These nitrates can eventually end up in the Gulf of Mexico and feed the development of oxygen-deficient "dead zones."

Microorganisms that live in wood, however, use a process called denitrification to convert those nitrates flowing from the field into nitrogen gas or nitrous oxide, which then diffuse into the atmosphere.

ARS microbiologist Tom Moorman and others at the agency's National Laboratory for Agriculture and the Environment in Ames, Iowa installed perforated plastic drainage pipes four feet below the soil surface of experimental crop fields. Then they dug trenches on either side of the pipes and filled the trenches with wood chips. They buried the trenches and the pipes, and then cropped the fields with a corn-soybean rotation for the next nine years.

Over the nine-year study period, the team found that the wood chip "bioreactors" consistently removed nitrates from the leachate - the solution formed by the leaching from the field. From 2001 to 2008, annual nitrate loss in plots with conventional drainage averaged 48.6 pounds per acre, but losses dropped to 21.8 pounds per acre in plots with the denitrification walls.

Compared to subsoil, the average denitrification potential of wood increased from 31-fold in 2003 to 4,000-fold in 2004.

The scientists also found that 50 percent of the wood buried between 35 and 39 inches deep had decomposed five years after it was buried, and that 75 percent of the wood buried at this depth decomposed after nine years.

These findings can help in the design of denitrifying wood trenches, since wood decomposition rates will be needed to calculate the functional life expectancy of a denitrification wall after it is installed.

Agricultural Research Service

Friday, January 4, 2013

Ditches Clean Field Runoff

Vegetated drainage ditches can help capture pesticide and nutrient loads in field runoff, U.S. Department of Agriculture (USDA) scientists report. These ditches — as common in the country as the fields they drain — give farmers a low-cost alternative for managing agricultural pollutants and protecting natural resources.

Until recently, the primary function of many edge-of-field ditches was to provide a passage for channeling excess water from crop fields. Many farmers controlled ditch vegetation with trimming or dredging to eliminate plant barriers that impede the flow of runoff.

Research by Agricultural Research Service (ARS) ecologist Matt Moore and colleagues, however, suggest that a slower flow has advantages. The scientists evaluated transport and capture of the herbicide atrazine and the insecticide lambda-cyhalothrin for 28 days in a 160-foot section of a vegetated agricultural drainage ditch in Mississippi. One hour after a simulated runoff event, 61% of the atrazine and 87% of the lambda-cyhalothrin had transferred from the water to the ditch vegetation. At the end of the ditch, runoff pesticide concentrations had decreased to levels that were generally non-toxic to downstream aquatic fauna.

Moore has also conducted work in California where vegetated drainage ditches helped mitigate pesticide runoff from tomato and alfalfa fields.

Sources: Agricultural Research Service

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