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5/6/2013 - 5/12/2013

Assess Your Soil Moisture Profile

By Mahdi Al-Kaisi, Department of Agronomy

It is welcome news to see the potential recovery from last year’s drought as the soil profile is fully recharged in most areas in the state. The moisture recharge of the soil profile is affected by many factors, such as soil texture, type of tillage, residue cover, soil slope, grass filter strips and many other conservation measures that enhance moisture recharge. The timing of rain events during early spring can cause significant damage, especially if soil temperature is low (frozen soils), leading to significant erosion and surface runoff. Therefore, monitoring soil moisture is important.

To determine the soil moisture status in a soil profile you can use two methods. One quick method is by monitoring your drainage tile flow.  If the tile is running with considerable flow that is an indication the soil is saturated and the excess water is moving through the soil profile by what we call “gravity flow.” The second method is to determine exactly how much water is held in the soil. To do this you must  know your soil texture at different depths at least down to five feet in one-foot increments and the soil moisture holding capacity at each foot.  (You can obtain this information from the soil survey or by contacting the NRCS office in your area).  After you obtain this information, add up the moisture available for the top five feet to determine the total amount of water in your soil profile

Most soils in Iowa have fine to moderate soil texture and the amount of water held at field capacity will be approximately 10-12 inches of water for the top five feet.  If this is true, it provides an excellent start for the growing season for both corn and soybean. Generally, corn needs approximately 24 inches of available water for the entire season. So at this point in time, if our soil profiles are at field capacity, we have almost 40-50 percent of the water needed for corn production. The other 50 percent or so must be provided through additional rain that hopefully will be spread evenly over the growing season. This is especially true during the high demand period for water use by the crop from June through August.  However, the timing of rain during the growing season is as critical as the amount of rain needed for crop production.

This good moisture amounts we have received over the past few weeks brings some challenges we need to be aware of in terms of managing soil and planting to minimize potential damage and eventually negative impact on yield.  Maximizing potential precipitation capture during subsequent rain events is highly important and is affected by how we manage crop residue and the intensity of tillage.  Slowing water movement across the field through conservation practices, such as grass filter strips and water ways, is a critical way of increasing water recharge and potentially mitigating any drought spells that may occur during the growing season.

Monitoring field conditions and soil moisture recharge will help assess the effectiveness of certain tillage and other management practices in achieving potential yield and improvement of soil quality.  Keeping a good record of your field conditions and operations early in the growing season may help explain positive or negative outcomes of the growing season for future management decisions/adjustments.


Mahdi Al-Kaisi is a professor in agronomy with research and extension responsibilities in soil management and environmental soil science. He can be reached at or 515-294-8304.

New Pesticide Record-Keeping App Now Available

By Kristine Schaefer, Department of Entomology

Iowa State University (ISU) Extension and Outreach worked with iOS app developer Rade | Eccles to develop the Pesticide and Field Records iPad app to help producers and agriculture businesses record and maintain pesticide application information. The free iPad app allows users to link information to specific field locations using satellite mapping and document pesticide application information needed to comply with state and federal record-keeping requirements.  The app also features a product search option that lists Environmental Protection Agency (EPA) product registration numbers and identifies restricted use products.

Development of the app was funded by the ISU Extension Pest Management and the Environment program and a grant from the EPA under assistance of the Iowa Department of Agriculture and Land Stewardship Pesticide Bureau.


Kristine Schaefer is a program specialist in the Department of Entomology. She can be reached at 515-294-4286 or

Bee Health in the News

By Matt O’Neal and Erin Hodgson, Department of Entomology

Last week saw two big events related to bees: the announcement by the European Union (EU) of a restriction on use of neonicotinoids insecticides and a joint report on the health of honey bees by the USDA and EPA. These events share a similar theme of preventing a widespread decline in pollinator abundance. In this article, we discuss what these events may mean for the on-going efforts to conserve pollinators and the future of insecticide registration in the United States.


Neonicotinoids banned in Europe

On April 29, 2013, the EU voted to restrict the use of neonicotinoids (specifically clothianidin, imidacloprid and thiamethoxam) beginning December 2013. Globally, these insecticides are used in a variety of agricultural and landscape settings, including the production of field crops, fruits, vegetables, and home gardens. Many neonicotinoids are systemic, capable of moving through the plant. Because they are used to combat a wide variety of pests, there is the risk that non-target insects, like pollinators, can be exposed to them. 

As noted by scientists in the EU, it is not clear the extent to which the widespread use of neonicotinoids is responsible for declines in pollinator health, abundance and diversity. As many news agencies have reported, the goal of this two-year restriction is to allow time for additional studies and data to be assessed, while potentially allowing for improvements in pollinator abundance.


Honey bee health in the United States continues to decline

The USDA and EPA released a summary report last week on the multiple factors influencing honey bee decline in recent years. In 2006, U.S. honey bee colonies first started experiencing large-scale, unexplained losses. Scientists described the sudden loss of worker bees and subsequent rapid colony death as Colony Collapse Disorder (CCD). Suspected factors contributing to CCD likely include a combination of pests, pathogens, pesticides, nutritional deficiencies and hive management practices.

There are 2.5 million colonies in the United States now compared to 6 million colonies in 1947. Since 2006, the United States is losing about 30 percent of honey bee colonies every year. At this steady declining rate, pollinated crops are at risk of not having enough bees. As an example, the almond industry needs about 1.5-1.7 million colonies for pollination services; that need is projected to increase to a point that exceeds the number of U.S. colonies.

The report indicated an important link between agriculture and honey bee health. Key findings include:

  • The parasitic Varroa mite is the single most detrimental pest of honey bees.
  • Honey bee breeding should focus on genetic diversity and select for resistance to pests and diseases.
  • A nutritionally poor diet can make colonies more susceptible to pests and diseases.
  • Sublethal exposure to pesticides also contributes to poor colony health.
  • Complex interactions between all the above factors likely responsible for honey bee declines.

Honey bees are responsible for $15 billion in increased crop value each year. Pollination services contribute to 33 percent of our diet. Photo by Adam Varenhorst.


What does this mean for U.S. farmers?

These two events share a similar topic, but there are some differences. One is that the EU ruling is addressing a decline in all pollinators, not just honey bees. Although honey bees are currently the most important pollinator of crops, many other species are used. Second, the EU is focused on restricting neonicotinoids, while the EPA report on CCD had an emphasis on all pesticides and other possible contributing factors.

As more is learned about the impact of any insecticide on honey bees, and potentially pollinators in general, there may be future restrictions to how neonicotinoids, or any pesticide, can be used in the United States. Every pesticide has to go through a regular, ongoing registration process with the EPA. Neonicotinoids are under close scrutiny by the public, and the upcoming labeled use could change to protect pollinators.


Best management practices for landowners

Although there are many factors that can negatively affect pollinators (specifically honey bees), there are some practices that landowners can adopt to help conserve them. 

  • Diversify the landscape around agricultural areas to improve foraging habitat. Include a variety of perennial, flowering plants. This could be native plants commonly found in Iowa prairies. Use this fact sheet for more ideas.
  • Use the recommended rate of seed lubricant for proper planting.
  • Be aware of wind speed and direction, especially near flowering plants.
  • Do not clean plant equipment/hoppers near fields.
  • Minimize off-site dust movement from treated seeds.
  • Alert local beekeepers of upcoming foliar pesticide applications using the Sensitive Crops directory.
  • Target pesticide applications to minimize exposure by reducing drift potential and only applying products when necessary.
  • Avoid spraying during daylight, especially morning hours. Bees visit flowers during the day. Spraying at dusk can reduce the potential of exposure.

To learn more about CCD and pollinator awareness, visit these websites:

“Europe bans pesticides thought harmful to bees”, April 29, 2013. The New York Times.

“Bee deaths: EU to ban neonicotinoid pesticides”, April 29, 2013, BBC.



Xerces Society 

Pollinator Partnership 


Matt O’Neal is an associate professor of entomology; contact him at or 515-294-8622. Erin Hodgson is an assistant professor of entomology with extension and research responsibilities; contact her at or 515-294-2847.

Apply Nitrogen or Plant Corn?

By John Sawyer, Department of Agronomy

The end of the optimal time for corn planting is quickly approaching. Getting corn planted should be a priority over making nitrogen (N) fertilizer applications. However, along with that decision there should be a plan to get N applications completed after planting and crop emergence. Switching products and application from preplant to sidedress requires availability of needed fertilizers and equipment. So have a plan in place.


Apply fertilizers if it does not delay planting

If planned fertilizer applications can be made without a delay in planting, then go ahead and make the applications. For materials such as urea or UAN solution (urea-ammonium nitrate 28 percent or 32 percent solution), those can be broadcast and incorporated with normal tillage before planting. This will work if applicators can stay ahead of tillage operations. Incorporate both of these fertilizers rather than leave them on the soil surface to avoid volatile N loss from the urea. If time is critical and application is to be made with pre-emerge herbicides, then surface application is an option, although more risky due to potential volatile loss and the applied N remaining on the soil surface (especially in no-till) if there is not sufficient rain to move it into the root zone. A rain (at least 0.25 to 0.50 inch within approximately two days after application) will eliminate volatile loss concern. Or, use a urease inhibitor to slow urea conversion, which provides more time for rainfall to move urea into the soil.


Anhydrous ammonia before planting

Anhydrous ammonia has some additional considerations. It must be injected, and the ammonia band will initially have high pH and considerable free ammonia, which can burn corn seedlings and roots. There is no exact “safe” waiting period before planting, and injury can happen even if planting is delayed for a considerable time period. The risk of ammonia injury depends on many factors, with several that are not controllable. For example, risk increases if application is made when soils are wet and then dry (ammonia moving up the injection track); with higher application rates; when soils with high clay content are wet (sidewall smearing of the injection track and ammonia moving toward the soil surface during application); and when soils are very dry and coarse textured (larger ammonia band). At the current time with the wet soils, the first risk is more likely and it is not uncommon for damage to be found later in the spring. A few things can reduce the risk of ammonia damage: wait and apply when soil conditions are good; have a deep injection depth (seven or more inches); wait several days until planting; if the injection placement relative to future corn rows can’t be controlled, apply at an angle; if the injection placement can be controlled with GPS guidance positioning technology, split future corn rows – with this system no waiting period is needed.


Options for sidedress N

If decisions are made to plant corn and then apply N sidedress, be certain to check that needed fertilizer products and application equipment will be available. Best options for sidedressing, in order from most to least preferable, include:

  1. injected anhydrous ammonia, UAN or urea,
  2. broadcast dry ammonium nitrate, ammonium sulfate or urease treated urea,
  3. surface dribbling UAN solution between rows,
  4. broadcast UAN, and
  5. broadcast urea.

Sidedress injection can begin immediately after planting if corn rows are visible or GPS guidance positioning equipment is used. Be careful so that soil moved during injection does not cover seeded rows or small corn plants. It is easiest to inject in the row middle and there is no advantage in attempting to place the band close to the row. Corn roots will reach the row middle at a small growth stage. Injected N can also be applied between every other row. That technique will provide equivalent response as when placed between every row. For many soils, when planting corn after soybean there should be adequate N in the root zone to meet the needs of small corn plants. For corn after corn, there is a greater chance that additional N is needed for early growth. Preplant or starter N can help meet that need, and is especially important if sidedressing is delayed significantly in either rotation.

Broadcasting urea or ammonium sulfate across growing corn might cause some leaf spotting or edge browning where fertilizer granules fall into the corn whorl. The chances of this happening increases with larger corn. As long as the fertilizer distribution is good and not concentrated over plants, the leaf damage should only be cosmetic.

Because UAN solution is comprised of one-half urea and one-half ammonium nitrate, it has less volatile loss concern than dry urea. A urease inhibitor with surface applied and non-incorporated urea and UAN will help reduce volatile loss. Rainfall will eliminate volatile loss and is needed to move surface applied N into the root zone.

Broadcast application of UAN solution across growing corn has the potential to cause leaf burn and reduced early growth. Depending upon the severity of damage, reduced plant growth may be visible for several weeks after application. Research conducted in Minnesota indicated that when corn plants were at the V3 growth stage (vegetative leaf stage defined according to the uppermost leaf whose leaf collar is visible – in this case three leaf collars visible), phytotoxic effects were worse at rates above 60 lb N/acre (rates applied were 0, 60, 90, and 120 lb N/acre), but damage was not permanent and did not adversely affect stand or yield. When plants were larger than the V3 stage, plant damage was worse and some yield depression occurred with the 120 lb N/acre rate. Many pre-emergence herbicides are applied using UAN as the carrier to minimize trips across fields. However, this strategy is only recommended prior to crop emergence. Almost all herbicides prohibit application in N solutions after corn has emerged. Check herbicide labels closely.

If N is going to be sidedress applied, then rates can be adjusted from results of the late spring soil nitrate test (LSNT). Soil samples, 0-12 inch depth, are collected when corn is 6-12 inches tall with rate adjustment based on the measured nitrate-N concentration. Using the LSNT could be especially helpful this spring when there is question about N supply in manured fields. The large rainfall this spring has moved carryover nitrate deeper in the soil profile. A concern with the LSNT this spring is that it will miss that nitrate and therefore over-estimate needed application.


Late sidedress N considerations

If corn becomes too tall for normal sidedressing equipment, it is possible to use high clearance equipment to apply N. The N source typically will be UAN solution, with equipment available to either dribble the solution onto the soil surface with drop tubes or shallow inject with coulter-shank bars (coulter-disk injected) or dry urea, which can be broadcast spread across the top of corn.

Research in Iowa has shown corn can respond to mid- to late-vegetative growth stage N application when there is deficient N supply, but there can be loss in yield potential. Reduced yield occurs more frequently when soils are dry at and after application (applied N not getting into the root zone) and with severe N stress. Best responses occur with sufficient rainfall shortly after application to move N into the active root zone.

If attempts to get N applied preplant or early sidedress have failed, or there are concerns about N supply from prior fertilizer or manure applications, then mid- to late-vegetative-stage application can be a helpful rescue. If possible, have some non-N limiting (approximately 50 percent more than normal rate) reference strips or areas in the field to use for comparison. These areas can be used to visually determine if corn would respond to additional N, or as a check to see if earlier N applications or carryover N is not sufficient. These reference areas are also needed for N stress sensing tools (such as chlorophyll meters or canopy sensors) to help guide application rates. These reference areas should be planned and N applied early in the season, or be field areas that are known to be non-N deficient. Plant and canopy sensing can begin when corn is at approximately the V9-V10 growth stage. If late N application is needed, it should be applied as quickly as possible and not later than the tassel stage.


In summary

  • Plant corn when conditions are fit, don’t rush.
  • Fertilize first if it does not delay corn planting.
  • In other situations, sidedress N.
  • Make certain needed N fertilizer products will be available.
  • Make certain sidedress equipment will be available.


John Sawyer is a professor in the Department of Agronomy with research and extension responsibilities in soil fertility and nutrient management. He can be contacted at

Iowa Organic Cropping Systems in the News

During the last decade, organic food sales have tripled in the United States, leading many Iowa producers to investigate organic farming. The USDA National Agriculture Statistics Service (NASS) stated that Iowa’s 467 organic farms had $60.7 million in sales in 2011, which led to a ranking of fifth place in the nation in the number of certified organic farms.

Organic cropping systems can provide similar or greater yields, higher soil quality and greater economic returns than a conventional corn-soybean rotation, according to research conducted by Kathleen Delate, professor of Agronomy and Horticulture at Iowa State University.  Delate has gathered data from a 13-year, side-by-side comparison experiment at Neely-Kinyon Research and Demonstration Farm. The research was published April 30 in the Crop Management journal.

Crop Management, a peer-reviewed journal of the Crop Science Society of America and The Plant Management Network, published research presented at the “USDA Organic Farming Systems Research Conference,” which took place in March 2011 at George Washington University in Washington, D.C.

In addition to Delate, USDA Chief Scientist and Under Secretary for Research, Education and Economics Catherine Woteki presented her insight and encouragement for organic systems as having significant potential for addressing the agricultural challenges of our time. Between 2002 and 2010, USDA contributed over $275 million to more than 2,400 organic research projects, five of which were coordinated by Delate and addressed critical issues from organic management of soybean rust to organic no-tillage systems.

Iowa State University’s Long-Term Agroecological Research (LTAR) experiment began in 1998 with support from the Leopold Center for Sustainable Agriculture. It is one of the longest running replicated comparisons of organic and conventional systems in the country. Cropping systems at LTAR were designed based on local organic farmer input and practices. They compare the following crop rotations, using identical crop varieties, with each crop in each rotation repeated four times every year:  conventional corn-soybean (two year), organic corn-soybean-oat/alfalfa (three year), and organic corn-soybean-oat/alfalfa-alfalfa (four year).

The corn yields in the organic C-S-O/A-A rotation averaged 99 percent of the average conventional corn yield, compared to 92 percent in the C-S-O/A rotation. Organic soybean yields were 5 percent and 4 percent greater in the C-S-O/A and the C-S-O/A-A rotation, respectively, than conventional soybean yields.

Organic oat and alfalfa yields, at 103 bu/acre and 4.4 tons/acre, respectively, exceeded county averages of 73 bu/acre and 3.3 tons/acre. Similar plant protection occurred in organic crops, without the use of petrochemicals, compared to conventional crops maintained with synthetic pesticides. Delate said they used a systems approach, based on multiple practices, including allelopathy and rotation, to manage weeds in the organic plots.

Co-author Cynthia Cambardella, USDA–ARS soil scientist (Ames, IA), found that soil organic carbon, total nitrogen, and extractable K and Ca were 5.7 percent, 9.5 percent, 14.2 percent and 10.8 percent higher in organic soils, respectively. Soil properties related to biologically active organic matter were up to 40 percent higher in organic soils. These results suggest that organic farming can foster greater efficiency in nutrient use and higher potential for sequestrating carbon. 

Co-author Craig Chase, Leopold Center for Sustainable Agriculture, calculated that the economic returns to land and management in 2010 were $510/acre in the organic C-S-O/A-A rotation compared to $351/acre in the C-S rotation and, throughout 13 years of the LTAR study, organic systems returned roughly $200 per acre more than conventional crops. Organic crops fetch a premium price in the market based on high consumer demand and, with the elimination of the need for expensive inputs like herbicides and synthetic fertilizers, economic returns will continue to rise. To sell a product as organic, the crop must be raised on land that has received no synthetic chemicals for three years prior to harvest.

Further information about other organic research or to learn more about how to become certified, visit the ISU Organic Agriculture webpage


Farming practices at the LTAR site

The conventional rotation in the LTAR experiment receives synthetic nitrogen amendments, herbicides and insecticides according to Iowa State University recommended rates. Skilled management has been an adequate replacement for synthetic chemicals in organic plots.

The organic corn plots receive local compost made from a mixture of straw and manure. Delate said they use a whole suite of practices to manage weeds in the organic plots, including timely tillage and longer crop rotations. Allelopathic chemicals from rye and alfalfa help keep weed populations under control, as does growing an alfalfa cover crop in winter, which provides cover for beneficial insects and animals. Organic corn and soybean plots receive an average of two rotary-hoeings and two row cultivations per season for weed management. To compensate for seedling losses that may occur during tillage, higher seeding rates are used.

A 30-foot buffer separates the organic and conventional plots to avoid any cross-contamination. The U.S. Department of Agriculture’s National Organic Program’s accredited agency, Iowa Department of Agriculture and Land Stewardship, certifies the organic plots annually. Crops are mechanically harvested with combines and hay rakers/balers.


Kathleen Delate is a professor with extension responsibilities in the Department of Agronomy. She can be reached at 515-294-7069 or at

Wet Conditions and Change in Soil Profile Nitrate

By John Sawyer, Department of Agronomy

I wrote an ICM News article February 21, 2013, that provided a summary of fall soil profile nitrate sampling results following the 2012 corn harvest. As I cautioned in that and other articles, the amount of nitrate-N that might remain for a 2013 corn crop depends on springtime rainfall. Unfortunately, much of Iowa has received considerable precipitation since soils thawed, especially the eastern two-thirds of Iowa. The two maps of the Midwest region show the total precipitation and deviation from normal since March 7, 2013. Tile lines are flowing again, and nitrate in the profile will move with percolating water. Not all of the precipitation entered the soil, but the amounts received and comments from ISU Extension and Outreach field agronomists who have sampled soil profiles this spring for moisture content suggest the soil profiles in most of the state have been recharged. Therefore, we have lost the opportunity to use much of the profile nitrate carried over from last year. Also, this spring’s precipitation after the dry fall reminds us why profile sampling for nitrate is not a routine practice in much of the Corn Belt.


Soil Profile Nitrate Changes Since Last Fall

Iowa State University Extension and Outreach field agronomists have been collecting soil profile samples this spring at the same locations as last fall. Unfortunately, with the spring weather not all sites could be sampled by the time of this article. However, with samples that have been collected so far, a few things are clear. One, samples collected before the large spring rains still had high nitrate-N amounts. Two, samples collected after the large spring rains show nitrate movement deeper into the profile. Three, samples collected after the large spring rains generally have less total profile nitrate-N than last fall. The following table has several examples. In most, but not all cases, the amount of nitrate-N decreased from fall to the spring sampling. The southwest Iowa samples were collected in early April (before the largest rains), with the rest collected in late April.


As mentioned in previous articles, spring preplant profile sampling near crop planting can sometimes give the best indication of the amount of nitrate-N in the soil profile that might carry over to a corn crop. This certainly is the case this spring. If you still consider there could be elevated nitrate-N levels in fields from last year’s drought-damaged corn, and the field will be planted to corn again this year, sampling is the best approach to determine if a nitrogen amount can be subtracted from the normal application rate. Profile sampling is most viable for the northwest area of Iowa where rainfall has been about normal this spring. You can refer to the previously mentioned ICM News article to find suggested sampling procedures.


Nitrogen Applications for 2013 Corn

From the soil nitrate samples collected so far this spring, it is clear that the carryover nitrate-N moved deeper into the profile or was lost to tile flow. With the cold soil temperatures this spring, it is unlikely nitrate was lost by denitrification. Reports from stream monitoring are indicating increased nitrate-N concentrations, as would be expected where tile drainage contributes significantly to stream flow. In many fields, the change in soil profile nitrate-N from last fall is quite dramatic, and unfortunately means less opportunity to account for nitrate-N carryover to 2013 corn crops. However, some fields still have carryover nitrate-N amounts that should be used to adjust nitrogen application rates. The precipitation maps are quite reminiscent of rainfall patterns of just a few years ago, and we know that in high rainfall years response to applied nitrogen is large, due to loss of soil derived mineralized N, carryover nitrate, and applied fertilizer and manure nitrogen. We’ll see if this weather pattern continues for 2013. With the overall wet spring and decrease in carryover profile nitrate, consider near normal nitrogen application rates. See the Corn Nitrogen Rate Calculator for suggested rates.


John Sawyer is a professor in the Department of Agronomy with research and extension responsibilities in soil fertility and nutrient management. He can be contacted at

This article was published originally on 5/13/2013 The information contained within the article may or may not be up to date depending on when you are accessing the information.

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