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9/24/2012 - 9/30/2012

Management Tips for Drought-stressed Forages

By Stephen K. Barnhart, Department of Agronomy

The Midwest has seen some of the most extreme drought conditions of recent memory. Some rain has come recently for most of this area, but not enough for most of us to feel comfortable. Pastures may still be in poor condition. Many hayfields are showing enough recovery to maybe yield at least one more cutting. Regionally, hay supplies are tight and prices are high. Forage management considerations are many. Here are some things to think about as you prioritize your options.


Hay and Pastures

The goal is to help keep perennial forage plants ‘perennial.’ During the fall weeks, perennial forage legumes and grasses respond to shortening days and cooling average daily temperatures and progress through their gradual “cold hardening” process. The genetics of the variety and local climatic conditions determine how cold tolerant the plant crown and taproot can be during the winter months. Most successfully winterhardened perennial forage legumes and grasses can withstand soil temperatures in the crown area to about 0 to 4 degrees F without crown tissue damage. At lower soil and crown temperatures, varieties and individual plants will vary in the degree of cold damage they may experience.

To best acquire their potential for winter survival, these forage plants should get five to six weeks of uninterrupted growth to accumulate root carbohydrates and proteins before going dormant for the winter. A ‘killing freeze’ is about 23-24F for several hours. Then, no more cutting or grazing until next season.

If you do decide to cut one more hay cutting or grazing, it is important to manage fall harvests or grazings to give the plants the best chance for strong winter survival. It is best to wait until at or after the killing freeze (23-24 F) for the last hay cutting, then leave a 5- to 6-inch stubble. It is not recommended to take a late season harvest from a new (2012) seeding.

The same goes for late season growth management of pastures. Try to allow three to four weeks of fall recovery before a killing freeze, and then, if you are going to graze again, leave an average of 3 inches or so of lower stem bases on the grasses.

The practical problem with these management strategies is that it involves removing livestock from pasture. And no more hay harvest – in an already hay shortage season. I can’t decide what is most important for you.



Fall is a good time to soil test and fertilize both hay and pastures with needed potassium (K) and phosphorus (P). This will help drought-stressed forage stands to overwinter and improve regrow and yields next spring. Applying 25 to 40 lbs of nitrogen to grass pastures during the last few weeks of their fall growth will aid in stimulating more fall tillering (branching)  and for more vigorous recovery in the spring. 

Give recovering hay and pasture stands time to ‘catch up’ or regain more vigor next spring.

If fall recovery was not favorable, or you did cut or graze late in the season in 2012, the recovering forage plant may still be under some physiological stress. Hay and pasture plants will benefit from allowing a bit more recovery and growing time next spring before they are cut or grazed. For best ‘recovery management,’ delay the first cut of alfalfa stands until they reach early- to mid-bloom.  For pastures, allow 3 to 4 inches of growth in the spring before livestock turnout.   


Repairing and Reseeding

Consider ‘interseeding’ or ‘frostseeding’ drought-thinned pastures   next late winter or early spring. Frostseeding is the broadcasting of legumes or additional grass seed in late winter when the last few weeks of night-freeze and daytime-thaw aids in seed coverage. Interseeding is using a drill to no-till legumes or forage grasses into an existing sod. Spring interseeding dates are mid-March through late-April.

 Frostseeding works best with legumes on the thinnest, least competitive sod areas. Grasses are generally more effectively established with interseeding than with frostseeding. With both frostseeding and interseeding, having the existing pasture sod  grazed closely  (like many of  our pastures following the summer drought stresses) reduces early season competition. Further competition for shade, sunlight and soil moisture can be reduced by timely and thoughtful rotational grazing for the first few months of new seedling establishment. For more details, see these ISU Extension and Outreach publications:  Pm-856, Improving Pasture by Frost Seeding, and  Pm-1097, Interseeding and No-till Pasture Renovation.


Stephen K. Barnhart is a professor of agronomy with extension, teaching, and research responsibilities in forage production and management. Barnhart can be contacted at (515) 294-7835 or by email

Aflatoxin and Grain Storage

By Charles Hurburgh, Department of Ag and Biosystems Engineering

In previous articles, we have discussed the aflatoxin issue from several angles – scouting, testing, use and handling. One key point is that once grain is dry and cold, or even just cold, the Aspergillus flavus fungus is rarely able to grow and produce more toxin. However, at least two problematic situations are arising –bin dryers operated at medium temperatures (below 120F) and high variability of moisture within fields.

The optimum temperature for aflatoxin production is 75-95F with moistures greater than 18 percent. A bin dryer operating with input air below 120F will “store” the grain during drying at these temperatures. If the bin is full, drying times of four to six days are not uncommon. In this case, grain already containing the Aspergillus fungus can experience increased aflatoxin levels.

The correction is to increase drying air temperatures beyond 120F.  Some bin drying systems with rapid stirring systems can go as high as 160F; others with less grain circulation may be limited to around 140F. Half batches will also help; shallower grain depth will increase airflow and cause less grain be held at higher moistures. It would be better in this case to dry two half batches instead of one full batch. The outside air temperatures have fallen enough that the corn in the field is now less likely to increase in toxin. Holding it in the field may be preferable to having it warm in a dryer.

High temperature batch and continuous flow dryers are not susceptible to this problem, but wet corn should be held in high airflow wet holding (to maintain cold temperatures) or in the field. As an example, today's conditions of about 80F and 30 percent relative humidity will hold aerated wet grain at about 45-50F because of evaporative cooling of dry air. This is below the growth conditions for Aspergillus flavus mold, although in time other more temperature resistant fungi will grow at those temperatures. Low temperature-natural air drying will also work under these conditions because the wet grain will not be warm enough to sustain the fungus.

In some cases, very high ranges of moisture are being experienced within the same field, for example 15 percent to 30 percent. Dryers will not equalize this moisture in one pass; there will be some wet corn remaining even after the average reaches 15 percent. Low temperature is the only control method for this situation; extra cooling cycles to bring the grain temperature immediately below 50F.

Corn will segregate somewhat by moisture if it is drop filled in a bin; this means that both the high moisture and the fines will collect in the center. It will be very important to remove the center core right away; in large bins (over 50 feet dia), two removals would be advisable.

Pay attention to the yield monitor moisture output to estimate which fields are likely to be a storage problem from moisture variations. Crop insurance will not cover quality issues after harvest.


Charles Hurburgh is a professor in the Department of Ag and Biosystems Engineering. He can be reached at 515-294-8629 or e-mail

2012 Iowa Harvest Exposure to Mold and Dust in Grain

By Chuck Schwab, Department of Agricultural and Biosystems Engineering

Grain dust is always a health concern for Iowa farmers and those working in the grain industry. Drought conditions this year may elevate human and animal health concerns because of increased dust and mold exposure. The Iowa Department of Public Health has issued 2012 Iowa Harvest Exposure to Mold and Dust in Grain, a fact sheet covering the following information.

The drought has created conditions favorable for an increase in dust and the production of aspergillus mold and associated aflatoxins. Exposure to low levels of grain dust during normal working conditions often causes reactions that are a nuisance, such as a cough, sore throat, nose and eye irritation, or feeling stuffed up or congested. People with chronic breathing problems or asthma may experience more symptoms or asthma attacks when exposed to high dust and mold levels.

Exposures to moldy and dusty grain, especially large exposures, may also cause two specific medical conditions with similar symptoms:

  1. Farmer’s Lung or Hypersensitivity Pneumonitis (FHP) – a fairly uncommon condition (one in 20 farmers) caused by a delayed allergic reaction to the dust. Repeated exposures can lead to permanent lung damage or limitations to work. A medical provider should be consulted.
  2. Organic Dust Toxic Syndrome (ODTS) – a more common toxic response to dust, molds, bacteria, or toxins in the grain dust. Recovery is usually in a few days, but a medical provider should be consulted.

Common symptoms include cough, headache, chest tightness, muscle aches, fever or generally not feeling well. If you have any of these symptoms, see your medical provider.


What you can do to protect yourself during harvest

  • Avoid direct exposures to dust whenever possible.
  • When working in extremely dusty conditions use a NIOSH-approved and certified “N-95” respirator that fits you properly. HOWEVER, consult your medical provider before using a respirator. Individuals with heart and lung conditions or other respiratory limitations should not use a respirator. N-95 respirators must be used only with a clean shaven face to ensure proper fit.
  • People with chronic respiratory health issues should avoid dust exposure.
  • If you have been exposed to large amounts of dust and you begin to feel ill, you should contact your medical provider for a proper medical evaluation.


Chuck Schwab is a professor in agricultural and biosystems engineering and the agricultural health and safety specialist with Iowa State University Extension and Outreach. He can be reached at or 515-294-4131.

The Moist Soil Test for Potassium and Other Nutrients: What's It All About?

By Antonio P. Mallarino, Department of Agronomy

A new private soil-testing laboratory began operations this fall in Iowa (based in Ames), testing for most nutrients on non-dried soil samples. This has generated many questions concerning the procedure and interpretations of test results because the common lab procedure for most nutrients is to dry and grind the soil samples.

The idea for testing non-dried soil samples is not new. It has been known for decades that drying soil may affect the extraction and measurement of certain nutrients, especially potassium (K). However, drying soil is commonly done by labs because it used to be a more practical sample handling procedure, and it standardizes soil moisture across all conditions. Iowa State University (ISU) research during the 1960s and 1970s, mainly greenhouse trials but some field trials, had shown that testing non-dried (field-moist) soil samples provided a better estimate of K fertilizer needs than testing dried samples, but both procedures provided similar estimates for phosphorus (P). Therefore, testing field-moist samples was adopted by the ISU soil and plant analysis laboratory, and it was the standard procedure for P and K during the 1970s and 1980s.

Iowa State University discontinued field-moist soil testing in 1988 (I was a graduate student at the time); not because it was a bad procedure but because no other lab adopted it and only ISU soil test interpretations were based on moist testing. The ISU lab made that decision even though Iowa research had shown the moist test was better for K, and it was among the tests recommended for the North-Central region by the NCR-13 committee (North-Central Regional Committee for Soil Testing and Plant analysis). Since ISU discontinued moist soil testing in 1998, the NCR-13 committee dropped the procedure from its soil-test methods publication.

The general attitude about moist soil handling and testing changed considerably this year, when the private lab that began operations in Iowa  developed a machine that easily handles moist samples and makes implementation of this procedure as practical as the common dry method (or even more practical because it avoids drying and grinding samples). This laboratory has been conducting soil testing research with Iowa soils since last year, some in collaboration with ISU.

Field research conducted during the 1990s showed much variability and uncertainty with K soil testing due to several reasons. So a portion of research my graduate students and I conducted since the early 2000s has focused on studying again if testing field-moist soil samples for K is better than testing dried samples.

The amount of extracted K is lower for the moist test than for the dry test at values usually optimum for crops or lower, but the difference decreases as levels increase. At extremely high levels, the moist test values can be higher than the dry test values. However, the moist and dry tests result in approximately similar values for P (by the Bray-1, Olsen, or Mehlich-3 methods), calcium (Ca) and magnesium (Mg) (by the ammonium-acetate or Mehlich-3 methods), pH, and buffer pH (by the SMP or Sikora methods). Figure 1 shows, as an example, comparisons for K and P extracted by the Mehlich-3 method from moist and dry samples.

Figure 1. Comparison of amounts of soil K, P, and Mg extracted by the Mehlich-3 test from many soil samples taken from Iowa fields. The dotted diagonal line indicates an exact 1:1 ratio.


Results from more than 300 field-response trials for corn and soybean confirmed that the field-moist test for K is better. Figure 2 shows the relationship between soil K measured by moist or dry tests and the relative yield response of corn and soybean to K fertilization. The graph for the dry test shows the current ISU interpretations for K, and further information including recommended fertilization rates is available in Extension publication PM 1688, A General Guide for Crop Nutrient and Limestone Recommendations in Iowa. The graph for the moist test shows the interpretations that ISU suggested for this test in the late 1980s. The fertilizer rate recommended for the Medium class used at the time was the amount to maintain soil-test values based on K removal, which in concept is similar to current Optimum class for the dry test. The old moist test classes relate to the recent yield responses almost exactly as they related to yield responses from research conducted during the 1980s (not shown).

Figure 2. Relationship between the relative yield response of corn and soybean and soil-test K measured from dried and moist soil samples (ammonium-acetate test, 6-inch sampling depth). VL, very low; L, low; O, optimum; M, medium; H, high; VH, very high.


Additional information and results will be presented at the North-Central Extension-Industry Soil Fertility Conference in Des Moines (November 14-15, 2012), the ISU Extension Integrated Crop Management Conference in Ames (November 28-29), and other ISU Extension conferences and workshops during the winter.

This fall the NCR-13 regional committee will publish an updated sample preparation chapter of the soil-test methods publication that includes the moist procedure. The ISU interpretations and fertilizer recommendations for the moist test will be developed in the future, as results for several ongoing field trials become available and can be merged with previous results. Interpretations for the moist test for P using Bray, Olsen, and Mehlich-3 (colorimetric or ICP procedures) should be similar to those for the dry test, since data already showed similar test results. The interpretations for the moist test for K likely will be similar to those suggested by ISU in the 1980s.


Antonio Mallarino is a professor of agronomy with research and extension responsibilities in soil fertility and nutrient management. Mallarino can be reached at or by calling (515) 294-6200.

This article was published originally on 10/1/2012 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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