Drought Induced Potassium Deficiency

Potassium deficiency in corn and soybean are more prevalent during times of drought. The diagnostic yellowing/chlorosis along leaf margins is seen in older leaves in both soybeans and corn. Potassium is responsible for water regulation (opening and closing of stomates) in the plant and is important to have adequate levels, especially during times of drought. Potassium is best managed through soil sampling and broadcasting fertilizer (or manure) to bring levels into the optimal range before planting. Below is video from Purdue University with Jim Camberato and John Obermeyer titled “Potassium Deficient Corn and Soybean During Drought”:

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Sulfur Deficiency in Corn

Sulfur deficiencies are becoming common in corn, especially in fields with sandy soils.  It’s a good idea to think about including sulfur in your fertility program on fields that have known sulfur deficiencies.  Possible sources include ammonium sulfate, K-Mag or SulPoMag, and manure.  Read below for more information from Richard Taylor, Extension Agronomist:

After visiting a great many fields over the past few days, I came to the conclusion that our efforts in controlling air pollution and especially sulfur (S) emissions have been very successful, perhaps too successful. The number of corn fields that are showing areas that of yellowing plants likely due to S deficiency is as great as or greater than I can ever remember seeing. I’m seeing plants with both the traditional S deficiency we all learned about in school where the plant shows a general chlorosis and stunting (Photo 1) and interveinal chlorosis that has been the hallmark of S deficiency in the past few years (Photo 2). Although many agronomists in the area were unsure of the interveinal chlorosis symptomology when it first appeared, Dr. Greg Binford did a few fertilization studies that seemed to confirm that S was responsible for the symptoms or at least could eliminate the symptoms.

Photo 1. More traditional sulfur deficiency symptom on corn with general chlorosis of the leaves and stunting of the plant which was about half the size of less affected plants.

Photo 2. Less traditional sulfur deficiency symptom on corn with severe interveinal chlorosis of the leaves along with stunting of the plant.

Many growers are already taking steps to reduce the impact of the ‘cleaner air’ by adding some ammonium sulfate to the corn starter fertilizer or to their sidedressed nitrogen (N). In Dr. Binford’s field trials, he did get a yield increase when S fertilizer was added; although in studies a number of years ago, I didn’t find a yield response to added broadcast S fertilizer. In many cases as the corn root system continues development, it is able to pick up S from the deeper soil layers and the deficiency symptoms disappear on their own accord. Another complication in the story is that we have changed from using the old superphosphate fertilizer (rock phosphate treated with sulfuric acid to make a 0-20-0 fertilizer) to new formulations, MAP, DAP and ammonium polyphosphates. This change has reduced the amount of S we were adding to our soils without consciously realizing it. I think as we go forward more and more growers will be using ammonium sulfate at some point in their cropping rotations to add needed sulfur to the topsoil.
You should keep in mind that S is either in an anion (negatively charged ion) form (SO42-) or is rapidly converted in warm, moist soil to the anion sulfate form. Anions such as sulfate and nitrate are subject to leaching loss from the topsoil. Dr. Tom Sims did find large quantities of sulfate in the deep subsoil layers of even the sandy soils in Sussex County, Delaware but the corn and other crops are not able to obtain S from these layers until much later in the growing season when the root system is nearly fully established. Early in the season, we are likely to find more and more fields showing S deficiency unless S fertilizer is regularly applied to the crops.

Taylor, Richard.  2012.  Sulfur Deficiency in Corn.  Weekly Crop Update.  Volume 20, Issue 11.  University of Delaware.  Online.  http://agdev.anr.udel.edu/weeklycropupdate/?p=4298

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Will Your Crop Suffer from Sulfur Deficiency this Cropping Year?

Good article from Richard Taylor, UD Extension Agronomist, regarding sulfur’s important role in crop production.

Past and recent emphasis has been placed on reducing sulfur (S) emissions from power plants, diesel vehicles, and other industries. The question of whether the Clean Air Act and other programs run by the Environmental Protection Agency are accomplishing their objectives can be answered by the farm community with respect to sulfur emissions. The answer growers would likely give is that yes the air quality programs have worked, but so well that their crops are increasingly showing sulfur deficiency symptoms, especially when grown on sandy, low organic matter, non-manured soils.
Why is S critical for maximum economic yields (MEY)? Sulfur is needed by a crop when making certain amino acids such as cystine and methionine that are vital components of many proteins. The entire factory output (yield) of a crop is dependent on proteins that make up the chlorophyll molecule, all the plant enzyme systems, the plant’s genetic material such as DNA, the assimilation function of legume rhizobia, and all the inter-related metabolic activity in the plant. The ideal nitrogen (N) to sulfur ratio in a plant is 15:1. Above that ratio, the S concentration is not adequate for MEY.
Sources for S include commercial fertilizers, atmospheric deposition, and manures or biosolids. The movement away from the old superphosphate (16 to 22% P2O5 and 12 to 14% S) to triple superphosphates in the late 1900s and then more recently to ammonium phosphates and ammonium polyphosphates (DAP, MAP, and others) has reduced the amount of S fertilizer applied without us consciously being aware of the trend. With the success of the Clean Air Act, atmospheric S deposition had dramatically decreased even before the very recent change over to ultra low sulfur diesel fuel. In addition, the emphasis on nutrient management planning to reduce manure application rates due to phosphorous buildup in the soil and the development of programs to help move poultry manure to areas without manure resources has also contributed to reduced S application rates.
Who should be concerned about the potential for S deficiency on their crops? The answer is that probably everyone but especially those growers with coarse textured soils, with soils low in organic matter, or with soils that have received enough rainfall or irrigation water to leach S below the crop rooting zone should be concerned. For shallow rooted crops such as wheat and barley, it is especially critical to ensure that adequate S is available during tillering and early growth and development. Growers should consider adding enough ammonium sulfate to their normal nitrogen application to provide from 20 to 30 lbs of S per  A in the first N application split in the spring.
If there is adequate S accumulation in the soil clay subsoil as determined with a deep soil test, S fertilization may not be a yield limiting factor on deep rooted crops such as corn. However, this does not mean that early season growth won’t be improved with the early season addition of some type of sulfate fertilizer. Even in high yield irrigated environments, such an application could help improve yield potential or at least not limit yield.
Some growers will want to rely on soil test results to make a decision on whether to add S fertilizer. These growers should be aware that the normal soil test depth of 0 to 6 or 0 to 8 inches is not as good an indicator of soil S status as it is for phosphorus and potassium. Sulfur is taken up by plants as the sulfate (SO42-) ion and as an anion (negatively charged ion) in the soil that is similar to nitrate. It is subject to loss via leaching and anaerobic conditions (similar to denitrification).
Sulfur deficiency symptoms vaguely resemble those of N except that S, unlike N, is not mobile in the plant so symptoms occur first on new growth. Sulfur deficiency is most often described as stunting with general yellowing or chlorosis of the plant. For examples, please review the photos at the end of this article.
The choices available for fertilizing with S include ammonium sulfate and potassium magnesium sulfate (K-PoMag) plus ammonium thiosulfate, calcium sulfate (gypsum), magnesium sulfate (Epsom salts), potassium sulfate, and elemental sulfur. Sulfate is immediately available for plant uptake whereas elemental So must be oxidized by the soil bacteria (requiring warm soil temperatures and adequate moisture) into sulfate before plants can absorb the S. Organic sources (manures, crop residues, biosolids) must undergo mineralization into inorganic sulfate before being available for plant uptake.
Other by-products such as derivatives from battery acid are sold as S sources but should be evaluated carefully by the grower to be certain that potential problems such as heavy metal contamination, non-available S forms, or injurious compounds are not present. Even then the S form in some by-products will need to be converted into plant available forms by the soil microorganisms and if S is needed immediately or if soil conditions are not favorable for this conversion yield potential could be impacted negatively. Certainly, any form other than the sulfate form is not appropriate in-season when deficiency symptoms indicate the immediate need for S.

Photo 1. Induced sulfur deficiency in corn grown in sand culture. Note reddening of lower stem, general chlorosis or yellowing especially of new growth, and stunting of the plant.

Photo 2. Field corn showing stunting and general chlorosis or yellowing, especially of new growth on sandy soil in southern Delaware.

Photo 3. Sulfur deficiency in barley grown on a very light sandy soil low in organic matter in Sussex County, Delaware. Note general chlorosis or yellowing especially of new growth and severe plant stunting.

Photo 4. Sulfur deficiency in wheat grown on a very light soil low in organic matter in Sussex County, Delaware. Note general chlorosis or yellowing especially of new growth and severe plant stunting.

Article by Richard Taylor, Extension Agronomist; rtaylor@udel.edu in the Weekly Crop Update Volume 19, Issue 1 – March 11, 2011.

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Nutrient Deficiencies in Corn

With cooler than normal temperature, wet soils, and heavy rainfall, we are seeing a lot of nutrient deficiencies in corn. The following is an article on the subject.

Once nutrients enter a plant, some are mobile and others are not. Mobile nutrients will cause deficiency symptoms to develop in older leaves, because nutrients present in the older leaves will move to new leaves to maintain the new growth. On the other hand, immobile nutrients will cause new leaves to show greater deficiency symptoms, while older leaves might be completely green.

Mobile nutrients that are known to cause deficiencies in corn include nitrogen, phosphorus, potassium, and magnesium. Sulfur is another nutrient that has been known to cause deficiency in corn, but it is not easily translocated in the plant. The only immobile nutrients known to cause deficiency in corn under some Delaware conditions are manganese and zinc.

Nitrogen (N) deficiency makes the older leaves (the bottom portion of the corn plant) turn pale or yellowish-green. The deficiency then starts to create a V shape, starting at the tip of the leaf. If the problem continues, the deficiency works its way up the plant from older to newer leaves. The stalks tend to be thin and spindly. N deficiency develops commonly in wet to saturated soils or under cool soil temperatures in the spring. N can leach out with heavy rainfall in light-textured (sandy) soils or can be denitrified in flooded soils when temperatures are warm. N deficiency can be induced after midseason or during other periods when soils tend to be dry. N deficiency can also occur in soils with large amounts of low-nitrogen-containing residues.

Phosphorus (P) deficiency causes a distinct dark green with reddish to purplish leaf margins, typically starting from the tip. The deficiency is observed in the older leaves. Stunted growth is also typical. At early development stages some hybrids show purple colors even though P is not deficient, while other hybrids might not show this coloration even when P levels are limiting. P deficiency symptoms normally disappear by the time the plant is waist-high. Since P is fairly immobile in the soil, any soil condition that limits root growth (cool temperature, wet or very dry conditions, compaction) can induce the deficiency.

Potassium (K) deficiency is observed as yellowing and necrosis (death) of the edge of older leaves. When the problem persists, this deficiency will continue to move up from older to newer leaves, while the top leaves may look completely green. K deficiency can cause lodging of the crop later in the season because stalks are thin and not strong. As with P, soil conditions that restrict root growth can induce deficiency, especially at early stages of development when the root system is small. Soils with low K buffer capacity can cause the deficiency if an appropriate fertilization plan is not followed.

Magnesium (Mg) deficiency appears in lower leaves as yellow or white streaking between veins. The leaves eventually become reddish-purple, and the edge and tip die if the deficiency is severe. Deficiencies have been seen in isolated situations in Delaware. The soils most likely to be deficient in Mg include acidic and sandy soils or low-CEC soils. Deficiency is more likely where calcitic limestone (CaCO3) rather than dolomitic limestone (CaMg[CO3]2) has been used in those soils.

Sulfur (S) deficiency causes yellowing of the foliage. S deficiency is often confused with N deficiency. Since S is not easily translocated, deficiency tends to be more visible in the newer leaves, differently from the older leaves with N deficiency. It is not uncommon to see interveinal chlorosis of the newer leaves. The condition is typically observed in soils with low organic matter (including sandy soils), low pH, and cold and wet conditions that reduce mineralization (release) of S from organic matter. Since S is leachable, corn will often grow out of a S deficiency once the root system taps into the S that has accumulated in the subsurface soil.

Manganese (Mn) deficiencies show up as yellowing between the veins of newer leaves of corn plants. In severe cases young leaves will be almost white in color. Mn deficiency is common on sandy soils low in Manganese with pH above 6.3. Manganese deficiencies also occur on some heavier soils with high pH but are rare on silt loams. Corn is less sensitive to Manganese deficiencies than soybean or small grain.

Zinc (Zn) deficiency is observed as light green to white stripes between veins or as wide bands starting at the base of the leaf and extending toward the tip of the newer leaves. The edge of the leaf as well as the midrib usually stay green. Usually corn can outgrow this problem, but in cases of severe deficiency, new leaves can be almost white. Zn deficiency is most commonly observed in soils low in organic matter, sandy soils with high pH (>6.5), cool and wet soils, or soils with very high P levels where Zn levels are marginal.

The unfavorable conditions for crop growth this spring mean that observing some deficiency symptoms in young corn plants should not be cause for immediate alarm. However, if deficiencies continue after growing season conditions improve, it is important to confirm any deficiency before trying to correct the problem. Since the visual symptoms are sometimes not clear-cut, it could be beneficial to collect affected plants and conduct tissue nutrient analysis.

Adapted from “Identifying Nutrient Deficiencies in Corn” by Fabián G. Fernández in the Bulletin newsletter from the University of Illinois.

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