Diagnosing nutrient deficiency symptoms in vegetables can be a challenge. They may be crops or plants with which we have little experience working with or the symptoms may not be expressed as clearly as in grain crops. Often these symptoms express themselves similar to herbicide injury or disease. So, how do we know if it is a nutrient deficiency? When beginning to diagnose a deficiency symptom, ask the client the following questions:

1) Can you provide a picture? When approached by a client to diagnose a problem, the first thing to ask for is a picture (or take a picture yourself). Without a picture we are only basing our diagnosis on verbal descriptions which are often vague and potentially misleading. Two types of pictures are helpful, a picture of the whole plant and a picture of the symptomatic leaf. A picture of the whole plant can let us know where on the plant the symptom is occurring (e.g. new leaf tissue or older leaves) and a picture of the leaf can let us know what tissue parts are affected (e.g. leaf margin or interveinal).

2) What is your fertilizer management? Try to obtain as much specific information as possible related to: how much N, P, K, and other nutrients were added, how the fertilizers were applied, when the fertilizers were applied, and in what form the fertilizers were applied (e.g. type of fertilizer, liquid or dry product, manure or compost). If the product is a specialty product, ask if they still have the bag or label. Ask about previous years applications and what crops were previously grown.

3) Have any other products been applied? Ask them for information related to timing and rate of any pesticide, insecticide, fungicide, or specialty product that has been applied. Ask about previous years applications as well.

4) What are the environmental conditions? Specific questions to ask are: Has the soil been excessively wet or dry? What were environmental conditions when you applied the product? Does the soil appear to be compacted? Is it difficult to push a shovel in the ground?

5) Have you had your soil tested recently? A recent soil test (within the past 3-4 years) may provide insight into the situation. Even some sort of knowledge of what their soil pH is can be incredibly beneficial for diagnosis. If they have not had their soil tested in the past 4 years, recommend a soil test.

If forwarding an issue to a colleague, attach photos and answers to all of these questions. This information will allow for a more accurate diagnosis and will provide a shorter turn-around time for recommendations. If a diagnosis cannot be made from a picture and a description of management and environmental conditions, the next step will be to recommend plant tissue and soil tests. Plant tissue sampling protocols (timing of collection and number of samples) can be found at www.soils.wisc.edu/extension/pubs/pa_sampling.pdf. There are two ways to use plant tissue testing: (1) to evaluate the nutrient status of leaf tissue and (2) to comparison between symptomatic and healthy plants. When testing to learn about the nutrient status of the leaf tissue, you are essentially comparing the nutrient concentrations in the symptomatic plant to predetermined values of sufficiency. If your plant tissue test value is in the sufficient range for a given nutrient, then that nutrient can be ruled out as the cause of deficiency. But if your plant tissue test value is below the sufficient range for a given nutrient, this does not necessary mean that this nutrient is the cause of the deficiency symptom. Sufficiency ranges are based on the best available knowledge, but may not reflect advancements in variety selection or differences in region. In addition, the sufficiency ranges pertain only to specific growth stages of the crop. If your deficiency symptom occurs during a growth stage not listed, then no sufficiency range is available. Thus, it is always preferable to diagnose a nutrient deficiency in vegetable crops by comparing them with healthy plants.

If there is a clear portion of the field that has the deficiency symptom, we recommend that you collect plant tissue samples and soil samples (0-6” depth) from the “deficient” area and plant and soil samples from the “healthy” area. If your plant tissue analysis comes back below the sufficiency range for a given nutrient, and if there is a soil test for that nutrient, the soil can be analyzed to determine if the soil is also deficient. It is important to note that even if the deficiency can be identified as a nutrient deficiency, there may not be adequate time to correct the deficiency. Also, even if there were time, the deficiency may have already caused a reduction in yield or quality.

When the area of production is small (often a small garden) and the area of infection is small the client may not have adequate plant tissue to make reliable comparisons. In these cases, we would recommend only submitting the symptomatic plant tissue for analysis along with a soil test. We will have to rely only on pre-established sufficiency ranges to make our diagnosis. Make sure the symptoms are well documented (multiple photos). The minimum amount of material that is needed for analysis is one gram; however, submitting such a small sample will not allow for re-analysis if necessary. When collecting leaf tissue samples, wipe off any soil particles and remove any foreign particles, but do not wash the samples. Use paper bags for storage and shipment. If the sample is to be mailed, then airdry the sample (near a heating vent or in the direct sun are two options). We also recommend the samples not be tightly packaged during transit. Soil samples should also be collected in paper bags. Collect 10 to 15 soil cores and composite them as one sample and mix thoroughly.

Further information on plant testing: http://www.soils.wisc.edu/extension/pubs/pa_sampling.pdf
Further information on soil testing: http://www.soils.wisc.edu/extension/pubs/A2100.pdf

When deciding to make any late-season, rescue application of nitrogen (N), you will need to evaluate your N management program relative to the potential for N losses. Heavy rainfalls can cause N losses due to leaching or denitrification; Dr. Carrie Laboski provides some guidelines in the previous Wisconsin Crop Manager article Assessing the Potential for Nitrogen Loss from Heavy Rainfalls (Laboski, 2011). If most of your N was applied pre-plant and heavy rainfall events occurred early to mid-growing season, then further investigation into N deficiency may be warranted. If you have split-applied your N fertilizer and there has been little potential for N loss, late-season N deficiency is unlikely. If you think that your corn may be N deficient during the late vegetative stages, scout your fields to evaluate any visual effects of N deficiency (e.g. lower leaves have yellowing in midrib, often called “firing” of lower leaves). Nitrogen deficiency (or sufficiency) can be confirmed with a plant tissue test. Follow the plant tissue sampling protocols set forth in the following documents to ensure reliable results: Troubleshooting fields using plant analysis (Laboski, 2010) and Sampling for plant analysis (Kelling et al., 2000).

If you have decided to apply a late-season application of N, the N fertilizer source and application method are important selections to make. Late-season foliar (or “over the top”) applications of UAN will result in moderate to severe burning. Research from the University of Missouri indicates that for 2 foot tall corn, broadcast applied 32% UAN results in much greater burn severity compared to broadcast ammonium nitrate or broadcast urea (Nelson et al., 2005). Between row applications resulted in little damage. The authors do not recommend broadcast applications of UAN when the corn is greater than 1 foot tall, while between row applications (of UAN and other N sources) are recommended when the corn is between 1 and 4 feet tall (when applications are warranted). It should be noted that this study was conducted on fields that had high leaching losses and were expected to respond to rescue applications of N (Nelson et al., 2005). Foliar application of UAN is not recommended after the V7 growth stage because the excessive burning of leaves can result in a yield decrease (Sawyer, 2003). Recently, foliar application of 28% UAN, at a rate of 10 gal/ac (30 lb/ac of N) was applied to corn at the V8 growth state at the Arlington Agricultural Research Station. This resulted in moderate to excessive leaf burn (Fig. 1 and Fig. 2). However, new leaf development has occurred and these leaves have no burn symptoms. We will have to wait to the end of the year to know the full effect of this application, but with other fertilizer sources available, it was clearly not worth the risk.

Foliar application of UAN has been identified as the least recommended option for N application (Fernandez, 2010). Early in the growing season, foliar application of UAN may still cause leaf burn, but it will not likely to lead to a yield reduction. Sawyer (2003) recommends no more than 90 lb/ac of N as UAN applied at the V3 stage or younger and no more than 60 lb/ac of N as UAN between the V3 to V7 stage. When the corn is too tall to risk damage during injection, UAN should be applied with drop nozzles between rows. If dry fertilizer is applied over the top of the corn canopy, urea and ammonium nitrate will cause some fertilizer burn if the granule falls in the whorl. It is best to apply dry fertilizer products when the canopy is dry.

In general, planned split-applications of N, even when they include applications made past V7, are preferable to applying all of the N pre-plant and relying on large (30 lb/ac or more of N) foliar applications as a rescue application. Split-applications prevent large amounts of applied N to be subject to environmental losses early in the growing season. If rescue applications are your only option consider the N source and application location. Stick to products like UAN, urea, or ammonium nitrate; slow-release fertilizers are not recommended late in the season. However, inclusion of NBPT (e.g. Agrotain®) would be beneficial for use with urea when surface applied to reduce volatilization (Fernandez, 2011). Further, avoid broadcast or “over the top” applications if possible to avoid risk of leaf burn and the potential decline in yield that would occur. If broadcast application of 28% or 32% UAN is your only option fully consider the potential tradeoffs between potential yield decrease (from leaf burn) and the potential for yield increase.

Figure 1. Corn canopy after foliar application of 28% UAN on July 12, 2011 (picture taken July 19, 2011).

Figure 2. Corn leaf after foliar application of 28% UAN on July 12, 2011 (picture taken July 19, 2011).

References (all links last verified on 21 July 2011):
Fernandez, F.G. 2010. Applying nitrogen after planting. http://web.extension.illinois.edu/state/newsdetail.
cfm?NewsID=17983
Fernandez, F.G. 2011. Applying nitrogen late in the game. The Bulletin, Univ. Illinois-Extension, 14:3,
July 8, 2011. http://bulletin.ipm.illinois.edu/article.php?id=1528
Kelling, K.A., S.M. Combs, and J.B. Peters. 2000. Sampling for plant analysis. (white paper) http://www.soils.wisc.edu/extension/pubs/pa_sampling.pdf
Laboski, C.A.M. 2010. Trouble shooting using plant analysis. Proc. 2010 Wisconsin Crop Management
Conference. 49:26-31. http://www.soils.wisc.edu/extension/wcmc/2010/pap/Laboski_analysis.pdf
Laboski, C.A.M. 2011. Assessing the potential for nitrogen loss from heavy rainfall. Wisconsin Crop
Manager, 18(6):61-63. http://ipcm.wisc.edu/WCMNews/tabid/53/EntryId/1191/Assessing-the-Potentialfor-Nitrogen-Loss-from-Heavy-Rainfalls.aspx
Nelson, K.A., P.C. Sharf, G. Stevens, and B.A. Burdick. 2005. Rescue Nitrogen Applications for Corn.
Missouri Soil Fertility and Fertilizers Research Update 2004, Agronomy Miscellaneous Publ. #05-01.
http://aes.missouri.edu/pfcs/research/prop403b.pdf
Sawyer, J.E. 2003. Pay attention to management needs of fertilizer products. Iowa State Univ.-Extension.
IC-490(4), p. 25-26, April 14. http://www.ipm.iastate.edu/ipm/icm/2003/4-14-2003/fert.html

The recent interest in the use of FGD gypsum as a soil amendment has resulted in some questions about the longevity of the S supply to crops because of the high rates of application.  This material is often applied at rates of 1 – 2 ton/a, which supplies may times crop S requirement.  Fifteen years ago I conducted a study that examined the efficacy of land applying crushed gypsum wallboard to alfalfa at several locations in Wisconsin.  The objective of that study was to examine the benefit of land application as opposed to landfilling.  The wallboard had a S content of 13.4 %, which would supply 268 lb S/ton, or approximately 10 X UW guidelines per ton for alfalfa.  Study rates included 1, 4 and 16 ton/a, which were applied and incorporated prior to seeding alfalfa.  Studies were conducted at four UW Agricultural Research Stations on a range of soil types.  More detail on the use of crushed wallboard for crop production can be found in UWEX Publication A3782.

Some suggest that because the plant available form of S is SO₄^2- , an anion, it is subject to leaching and will quickly be depleted from the rootzone.  Sulfur, like nitrogen, is cycled in the soil and will become a component of the soil organic matter in the plowlayer, where it will not be detected by a soil test.  Over time this S will be mineralized as plant available S.  Therefore, while some S is expected to leach, a substantial amount may be retained in the soil organic matter.  This is why soil test S by itself is not necessarily a good predictor of S nutrition and currently other factors are used to predict S need via the Sulfur Availability Index.

Table 1 shows the effect of wallboard application rate on the soil test S and forage S concentration.  Materials were applied and incorporated prior to seeding in late April and early May of 1995.  Soil samples were collected each July and the forage S values are for the second cutting each year.  The annual precipitation received in the study years was either at or below average, with the exception of somewhat higher values at Spooner in 1995 (35.3 in.) and Ashland in 1996 (38.1 in.).   These data show the rapid increase in soil test S in 1995, which moderated in 1996, and for the 1 ton/a rate were similar to the control in 1997.  The S concentration of the harvested forage responded to the application of S and responses were greater at the sites in northwestern Wisconsin, where historically S response has been more common.   A tissue concentration in the range of 0.25 – 0.50 is considered sufficient for the top six inches of alfalfa sampled at the late bud to early flower growth stage.  The only significant yield responses observed in the study were at Ashland and Spooner in 1997 (data not shown), which had relatively low forage S concentrations.

These data suggest that large gypsum applications will initially cause a large increase soil test S, which over a period of two years return close to background when applied rates of 1 – 2 ton/a.  Rates greater than this are not economical and creates a risk on lighter soils where the excessive Ca displaces other cations such as K and Mg, which may be leached from the plowlayer.  The plant analysis data shows the potential supply of S is still high and likely comes from S mineralized from organic matter.  Over the years since the wallboard research was conducted S deposition in precipitation has decreased, increasing the potential for S response in crops.  Applications of 1 – 2 ton gypsum/a should supply adequate S for alfalfa grown in normal rotations.  Producers concerned about S nutrition should use a combination of plant analysis and soil testing to confirm the need for S.

Table 1.  Effect of large applications of crushed gypsum wallboard on the soil test S and S concentration of harvested alfalfa forage at four Wisconsin locations, 1995 – 1997.

Land rolling is the practice of pulling large cylindrical rollers over fields with the objective of smoothing the ground.  Typically the practice is conducted just prior to or after seeding soybean, but some producers have conducted rolling well into the season over relatively large plants.  The rollers press stones into the soil and break up corn root masses to provide a smooth, uniform surface area for harvesting.  According to Mahdi Al-Kaisi of Iowa State University land rollers may cost over $50,000, with an average cost of $6.55 per acre according to the Iowa State Custom Rate Guide

Reported benefits of rolling include fewer machinery problems because soil and stones are not picked up and therefore damage to the cutting bar or components within the combine is avoided.  The smoother surface allows for the lower setting of the head permitting the harvest of low hanging pods.  Producers that use the practice claim less stress when harvesting and the ability to harvest at somewhat greater ground speeds.  Concerns include the cost of conducting the rolling operation, the moderate compaction of the soil that may affect emergence or damage plants if emerged, the potential for greater runoff because of reduced infiltration from surface compaction, and the loosening of crop residue that may be blown off the field.  Research studies examining rolling have not shown consistent yield benefits.

The practice of land rolling is more common in states just to the west of Wisconsin.  Evaluations were recently conducted in Iowa by Mahdi Al-Kaisi of Iowa State University and Jodi DeJong-Hughes of the University of Minnesota.  Jodi presented her findings at the recent Corn Soy Conference in Wisconsin Dells and together they published an article in Iowa State’s Integrated Crop Management News in January 2011.  The result of their studies presented in the accompanying table did not show a yield response relative to rolling, with the exception that rolling when plants are at the 6^th trifoliate stage reduced yield because of plant damage.

Response of soybean yield to ground rolling in Minnesota and Iowa, 2009 – 2010.

Source: Dr. Madhi Al-Kaisi et. al., Iowa State University.  Published in the Iowa Crop Manager, 2011

Currently no research on land rolling has been conducted in Wisconsin.  Like any soil management practice growers should consider the associated costs and benefits associated with the practice.  Research has not demonstrated that land rolling will produce a positive yield response, but my conversations with growers that have adopted the practice indicates a general satisfaction that they see relative to harvest management efficiency and reduced potential for machinery damage.  Beyond the cost issue, the major concerns that exist with rolling are the potential for increased runoff and erosion from reduced infiltration and the loss of residue by wind once loosened by the rolling operation.

Rolling emerged soybean (Photo courtesy of Mahdi Al-Kaisi, Iowa State Univ.)

HayandForage.com and Carrie Laboski wrote an article concerning sulfur and potassium deficiencies in alfalfa. Read this article on hayandforage.com

Current UWEX nitrogen (N) application guidelines for oats are 40 lb/ac for soils with 2 to 10% organic matter and 60 lb/ac for soils with less than 2% organic matter. When oats follow soybean, UWEX guidelines would suggest no need for N fertilizer on most mineral soils, as there is a 40 lb/ac soybean rotation “N credit”. This credit reflects the fact that yields of small grain crops following soybean are optimized with 40 lb/ac less N compared to when following corn or other grain crops. This N credit does not mean that growing soybean results in an extra 40 lb/ac of N in the soil at the end of the season. In fact, the net N balance during a soybean is often zero and become negative with greater yields (i.e. more N is removed as grain compared to the amount of N fixed by the plant).

To evaluate optimum N rate for oats following corn or soybean, we established an N rate study in 2010 at the Lancaster Agricultural Field Station. We applied four different rates of ammonium nitrate fertilizer (0, 40, 80 and 120 lb/ac of N), when oats were 2 inches tall. The oat variety was Esker and planted April 14^th, 2010 at a rate of 3 bu/ac. Deep soil cores (0-1’ and 1-2’) were collected prior to planting, one value per rotation, and the PPNT values were 85 ppm following soybean and 87 ppm following corn. While the PPNT has not been calibrated for oats, we can use the PPNT to confirm that these sites were similar in amount of residual nitrate. For comparison, based on these PPNT levels, if we were growing winter wheat, we would reduce N applications by 35 to 37 lb/ac of N (subtract 50 ppm from PPNT value). Continue reading this article on WCM.

With the current price of corn in the $7/bu range, growers and agronomists have been asking if they should reconsider their N application strategy with regard to rate, time of application, and use of inhibitors or slow release products. This article will address the issues that growers and agronomists need to consider when selecting a N application rate.

Selecting a N fertilizer rate. Using the MRTN (maximum return to N) approach to selecting a N fertilizer rate is just as valid this spring as it is any spring. A key thing to remember is that when N and corn price levels increase, risk increases. The N rate guidelines are provided in Table 1. The first step in selecting an appropriate N rate is to identify the previous crop and soil yield potential for your field. The soil yield potential is based on soil properties such as water holding capacity, drainage class, depth of root zone, and length of growing season. A table listing each soil’s yield potential can be found in UWEX publication A2809 Nutrient application guidelines for field, vegetable, and, fruit crops in Wisconsin. Continue reading this article on WCM

There has been much recent interest in planting forage radish or oilseed radish (Raphanus sativus) following winter wheat or corn silage harvest. Some of the forage radish varieties sold as a cover crop seed are cultivars of the Daikon variety (a Japanese table radish) and have been selected for large taproot size. These selections, derived from radish grown at the University of Maryland, are trademarked and sold as Tillage Radish™ and GroundHog™. Oilseed radish cultivars are also available (e.g. Adagio), may not trademarked, and generally have stubbier taproots compared to cultivars of the Daikon forage radish. Some radish is sold as VNS (variety not stated). Use caution when purchasing VNS seed as it has not been selected for large taproots and you will not know what type of radish you are getting. While research related to using radish as a cover crop is in its infancy, there are some guidelines that we can suggest for use. In general, proceed with care if interested in incorporating radish as a cover crop into your cropping system. Continue reading this article on WCM

The interest in the use of gypsum in crop production has increased in Wisconsin for a variety of reasons. The installation of “scrubbers” at coal-fired power plants has reduced S emissions substantially, thereby significantly reducing the amount of S deposited in precipitation. Consequently many producers and consultants are now seeing evidence of low S for the first time and the use of S-containing fertilizer is on the rise. While there are numerous S fertilizer sources (e.g. ammonium sulfate, potassium sulfate, sulpomag), gypsum is typically the least expensive. Furthermore, a byproduct of some scrubbers is high quality gypsum, which is coming from SE Wisconsin powerplants operated by We Energies. This material is known as FGD (flue gas desulfurized) gypsum and is being marketed as Gypsoil^TM . Continue reading this article on WCM

Sulfur (S) and potassium (K) are two nutrients that Wisconsin alfalfa growers should watch based on an alfalfa plant analysis survey conducted in 2010 by the University of Wisconsin. Samples were collected from the top six inches of new growth when the crop was in the bud to first flower stage. Thirty-nine samples were collected from 17 counties in Wisconsin (Figure 1), with 37 samples collected prior to first cutting (May 19 to June 10) and the other two samples collected prior to second cutting (June 28 to July 13). Eight of the samples submitted came from fields, or portions of fields that were poor in appearance and noted a being lighter green and shorter/stunted. Tissue S concentrations were considered low (less than 0.25% S) in 88% of these samples and K concentrations were found to be low (less than 2.25% K) in 75% of the samples. A vast majority of samples (31 of 39) came from fields that appeared normal. In normal appearing fields, tissue S levels were low in 58% of the samples and K levels were low in 45% of the samples. For all samples submitted, 64% were low in S, 51% were low in K, and 31% were low in S and K. The range in tissue S concentrations was 0.11 to 0.34% S, while for tissue K it was 1.50 to 3.16%. Other tissue nutrient concentrations did not suggest widespread deficiencies, though boron (B) was low in 10% of all samples. Continue reading this article on WCM