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.

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

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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.

Sources:
Agricultural Research Service

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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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Urbanization Hurting Bumblebee Populations

Paved roads and development in rural areas is adversely affecting ground-nesting  bumblebees, an important native pollinator, according to research at The University of Texas at Austin and the University of California, Berkeley.

"Honey bees are declining precipitously, and wild bees have also been exhibiting population declines across the globe. Native bees provide critical pollination services for fruit, nut, fiber and forage crops," says professor Shalene Jha, lead author of a study suggesting management strategies that reduce the local use of pavement and increase natural habitat within the landscape could improve nesting opportunities for wild bees and help protect food supplies around the world.

The study also suggests that increasing the number of species-rich flowering patches in suburban and urban gardens, farms and restored habitats could provide pathways for bees to forage and improve pollination over larger areas.Animal pollination is estimated to be worth over $200 billion in global crop yields.

In addition to finding that pavement negatively affects the bees, the scientists discovered that:

> Bees will move longer distances to find patches of flowers that are rich in species; it's not floral density that determines how far a bumblebee will fly, but floral diversity.

> Bees will also forage further away from their home nest if the surrounding landscape is less heterogeneous.

"In combination with earlier work showing that bumblebees have become rare in agricultural landscapes, our study suggests that farmers could promote these valuable pollinators by diversifying crop types and by planting cover crops and flowering hedgerows to enhance floral diversity," says environmental scientist Claire Kremen of the University of California, Berkeley.

Bumblebees nest in the ground, and each colony contains a queen and a force of workers. As with honeybees, all of the bumblebee workers are sisters who spend some of their time flying around searching for flowers from which to collect pollen and nectar to feed the larvae back in the hive.

Unlike honeybees, which are not native, bumblebees do not make harvestable honey. They do, however, provide important pollination services to plants.

Sources:
Claire Kremen, University of California, Berkeley; 510-367-2100
Shalene Jha, University of Texas at Austin; 248-719-5766

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Protecting Stored Grain Through Fall and Winter

As most dryland corn producers know, the only defense against mycotoxin contamination in corn is to manage the grain moisture content and grain temperature to minimize mold growth in the grain. Recommendations to protect stored grain:

Dry dryland corn down to 13% moisture if it’s to be stored for more than a month.

Run aeration fans whenever the air temperature was 10 degrees cooler than the grain temperature since the rate of mold growth is slower at cooler temperatures.

Cool stored grain down to 30°F (plus or minus 5 degrees) to stop mold growth. If the grain has not been cooled to the recommended temperature for late fall and winter, do so soon, especially if the grain will be kept into the new year.

In fall and winter, grain next to the bin wall will be cooled while grain in the center of the bin will stay warmer. The difference in temperature can result in convection air currents migrating through the grain (Figure 1). The warmer air in the center of the bin rises and the grain next to the cold bin wall sinks. When the warm rising air encounters the colder air at the top of the bin, the escaping air can go below the dew point temperature of the rising air and deposit moisture on the grain. This can create a wet spot in the top-center of the bin.

If the grain is warm enough for microbial activity, a hot spot can form and molds can grow, even in winter. This includes molds that can produce mycotoxins.

Run the aeration fan(s) at least once a month when the humidity is low and the ambient air temperature is 30 to 35 degrees. To conduct a preliminary check on grain quality, start the aeration fan(s), then climb up and lean into the access hatch. If the air coming out of the hatch is 1) warmer than you expected, 2) has a musty order or 3) If condensation forms on the underside of the bin roof on a cold day, continue to run the fan(s) long enough to push a temperature front completely through the grain.

A rule of thumb is, the time (hours) to push a temperature front through a bin of grain is 15 divided by the airflow-cubic-feet per minute per bushel cfm/bu.

For example, a bin used for drying grain should be able to produce about 1.0 cfm/bu so it would take about 15 hours to push a temperature front through the grain (15/1 = 15). In another example, a bin equipped with a fan able to push only 0.3 cfm/bu could push a temperature front through in 50 hours (15/0.3= 50).

Source: Tom Dorn, Extension Educator, Lancaster County, University of Nebraska–Lincoln

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New Potatoes Rich in Carotenoids

Scientists with USDA's Agricultural Research Service (ARS) are breeding new yellow-fleshed potatoes with carotenoid levels that are from two to 15 times higher than those of the popular Yukon Gold variety.

Carotenoids are of keen interest because they appear to protect against age-related macular degeneration and perhaps against cataract formation.

ARS plant geneticist Kathy Haynes discovered wild potatoes with intense yellow flesh that have about 23 times more carotenoids than white-flesh potatoes. By crossing these wild potatoes with cultivated types, Haynes  developed high-carotenoid potatoes for commercial markets.

Haynes and her colleagues introduced a new potato named "Peter Wilcox" in 2007 which has become popular in niche markets. The overall carotenoid levels in the purple skinned and yellow fleshed potato are more than 15 percent higher than those in Yukon Gold.

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Artwork: Peter Wilcox potatoes. Photo by University of Florida.

Sugar is Death to Aphids

A treat for humans, sugar can be deadly to aphids.


Agricultural researchers are now exploiting this vulnerability as an insecticide-free way to control insect pests.

"There is an urgent need for new strategies for insect control, because insects are developing resistance to traditional broad spectrum insecticides," says professor Angela Douglas of Cornell University.

Douglas and fellow scientist Georg Jander are genetically engineering plants to protect themselves by increasing the sugar in their sap.

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