Nutrient Management of Soybeans with the Potential for Asian Rust Infection

Paul E. Fixen, Cliff S. Snyder, Harold F. Reetz, Jr., T. Yamada and T. Scott Murrell*
Potash & Phosphate Institute (PPI)/Potash & Phosphate Institute of Canada (PPIC)
Foundation for Agronomic Research (FAR)


The focus of research and management for controlling Asian rust in soybeans has been on fungicides and genetic development. This approach is clearly justified considering the aggressive nature of the pathogen involved and what is known about managing fungal diseases. However, much is also known about the influence of plant nutrition on susceptibility and tolerance of crops to diseases. It seems reasonable to study the influence of nutrients in managing Asian soybean rust as part of overall management to control the disease. Some examples follow of situations where mineral nutrition plays a significant role in the severity of disease development.

Potassium (K)
low soil K levels and K fertilization has reduced occurrence of leaf spot disease resulting from Helminthosporium in Coastal bermudagrass. These observations are of particular importance when the current soil K status of major soybean growing areas is considered (Fixen, 2002; see figure). Where K nutrition is inadequate, there is potential for crops to be more susceptible to disease.

Chloride (Cl)
Application of Cl, usually in the form of KCl (muriate of potash), has been shown to reduce the severity of numerous fungal diseases (Fixen, 1993). These include take-all, common root rot, tan spot, Septoria, leaf rust, and stripe rust in wheat; common root rot, spot blotch, Fusarium, and root rot in barley; stalk rot in corn; stem rot and sheath blight in rice; hollow heart and brown center in potatoes; Fusarium yellows in celery; downy mildew in pearl millet; gray leaf spot in coconut palm and sudden death syndrome in soybean (Sanogo and Yang, 2001). Several studies have demonstrated that cereal varieties may differ in response to Cl and the associated disease effect.

Manganese (Mn)
Although studies have shown that several micronutrients can be involved in development of resistance in plants to both root and foliar diseases, Mn is thought to be the most important (Graham and Webb, 1991). Manganese is usually lower in tissues susceptible to fungal, viral, and bacterial pathogens than in resistant tissues (Huber and Wilhelm, 1988). Effects of Mn on plant disease severity have been reported for numerous crops and diseases including root rot, take-all, powdery mildew, leaf rust, and stem rust in cereals; damping off and wilt in cotton; late blight, stem canker and scab in potato and blight in soybean. As with Cl, studies have shown differences among varieties in response and some have observed that many newer glyphosate resistant soybean varieties have a reduced capacity to either take up or translocate Mn (Huber et al., 2004).

Phosphorus (P)
The likelihood of stem and leaf disease problems increases with crop stress and nutrient shortages and imbalances. Leaf rust in winter wheat has been reduced and yields increased by providing adequate P and K nutrition to the crop (PPI, 1999). A study on the effect of NPK fertilization on rust infected soybeans in the Philippines showed some rust suppression when either P (superphosphate) or K (KCl) was applied, but showed the greatest suppression when both nutrients were used.







Questions
The obvious challenge is that little is known about the specific effects of these nutrients on Asian rust in soybeans. Fungicides are clearly the major management tool in managing the disease, but it is possible that within the context of fungicide application timing or frequency and soybean production economics, there is a role for more intensive management of nutrients needed by the soybean crop. This photo from a rust infected soybean field in Brazil where application misses resulted in “checks” for KCl and fungicide application appears to show effects of both on the disease. Anecdotal evidence such as this, along with a history of verified disease-nutrition interactions, lead to numerous questions. Some follow.

  • Does potash (KCl) application influence rust development in soybeans similar to its effects on cereal crops?
      • If it does, is the effect due to K or Cl?
      • Do soybean varieties differ in reaction as do wheat varieties?
      • What is the effect of fungicide application on K or Cl response?
      • Is there a combination of KCl and fungicide use that offers a more profitable management strategy under certain conditions?
      • Is there reason to apply at least a portion of the crop rotation’s K need as KCl prior to soybean establishment to capitalize on positive disease effects (if Cl is involved in rust suppression and considering that it is highly leachable, earlier application may not be effective)?
  • Does the Mn status of soybean plants influence disease development or response to fungicide application?
      • Do glyphosate resistant (RR) varieties differ from conventional varieties?
      • Does glyphosate application influence Mn levels and disease development?
      • Does foliar Mn application to low Mn plants influence disease development or yield?
  • How important is P nutrition in reducing the impact of rust on soybeans?
      • Are optimum soil test P levels and plant tissue levels the same for soybeans under pressure from rust?
      • Is there any benefit from applying P fertilizer directly to soybeans that will likely be under rust pressure?

Research and On-farm Trials
An immediate need exists to develop answers to these questions. Both on-farm strip trials conducted with field-scale equipment and more complex small plot experiments designed to assess interactions could be conducted. Examples follow.
    Small Plot Study
    • Factors (3x3x3 factorial = 27 treatments; minimum of 4 reps)
        • Main plot – Fungicide/Mn (3): Check, fungicide, foliar Mn
        • First split - Variety (3): Two RR, one non RR
        • Second split - K vs Cl (3): Check, KCl, CaCl2 (rate of 50 lb Cl/A)
    • Measurements
        • Soil – standard soil tests and Mn (0-6 inch); K, nitrate and Cl incrementally to 2 feet
        • Plant – progressive rust severity, tissue K, Cl and Mn, grain yield, seed size
    Field Scale Strip Trials
    • Many different options; suggest multiple sets per field
    • Four treatment option: Check, fungicide, KCl, fungicide + KCl
    • Monitor daily during rust season
    • Select a set of similar fields planted to different soybean varieties
    • Take photos and grain yield
    Sentinel plots
    • Create plots that will have high probability of being the first to develop rust if innoculum is present.

Management in 2005
So, we have theories and lots of researchable questions concerning holistic management of soybeans under pressure from Asian rust. What should soybean growers do in 2005? The science of nutrient management of soybeans and soybean rotations has not changed. In many respects, there’s just one more reason to correctly manage nutrients for the soybean crop. Suggestions follow.
    • Be sure soil tests are up to date on fields going into soybeans and that samples have been taken using a sound sampling protocol that captures the manageable variability of the field.
    • Follow the recommendations resulting from the soil tests.
    • If potash (KCl) and P have not been applied prior to soybeans in the rotation, now might be a good time to make a shift to applying a portion of the rotation needs at that time. On soils with poor internal drainage where salts accumulate in the root zone, such as the flatwood soils of the southeastern U.S., soil Cl levels will likely be very high and high rates of KCl may contribute to Cl toxicity for Cl sensitive soybean varieties (Parker et al.,1986). Generally, Cl toxicity on soybeans appears to be limited to soils naturally high in salts and those being irrigated with high Cl (>100 ppm) water (Snyder et al., 1995). Local agronomists or advisers should be consulted on appropriate KCl rates for local conditions.
    • As fields are being scouted for rust, take the opportunity to collect plant tissue samples for nutrient analysis. This is an excellent time to verify that the nutrient management program in place is indeed providing balanced nutrition to the crop and giving it the greatest opportunity to do battle with whatever stress it encounters … be it disease, drought, compaction, or some other challenge of Mother Nature or of man. Be sure to include Mn in the elements tested.
    • Learn as much as you can. Read. Leave check strips. Observe. Record.

References
Fixen, P.E. 1993. Crop responses to chloride. In D. L. Sparks (ed) Advances in Agronomy, Vol. 50. Academic Press, Inc.
Fixen, P.E. 2002. Soil test levels in North America. Better Crops 86(1):12-15.
Graham, R.D. and M.J. Webb. 1991. Micronutrients and disease resistance and tolerance in plants. Pp. 329-370. In J.J. Mortvedt, F.R. Cox, L.M. Shuman, and R.M. Welch eds.) Micronutrients in Agriculture. 2nd edition. Soil Science Society of America.
Huber, D.M., J.D. Leuck, W.C. Smith, and E.P. Christmas. 2004. Induced manganese deficiency in GM soybeans. Proceedings of the North Central Extension-Industry Soil Fertility Conference 20:80-83. Potash & Phosphate Institute, Brookings, SD.
Huber, D.M. and N.S. Wilhelm. 1988. The role of manganese in resistance of plant diseases. In: Graham, R.D, R.J. Hannam, and N.C. Uren (eds). Manganese in Soils and Plants. Kluwer Academic Publishers, Dordrecht, The Netherlands. pp 155-173.
Miller, Travis D. 1998. Chloride fertilizer effects in winter wheat and interactions with foliar fungicides under severe leaf rust pressure. Better Crops 82(1):24-26. and http://www.ppi-ppic.org/chloride.
Parker, M.B., T.P. Gaines and G.J. Gascho. 1986. Sensitivity of Soybean Cultivars to Soil Chloride. Res. Bul. 347. The Georgia Agric. Exp. Stat., U. of Georgia, Athens.
Piccio, V.L. and N.S. Franje. 1980. Rust incidence in soybean (Glycine max (L.) Merr.) as affected by varying levels of NPK applied alone and in combination. Soybean Rust Newsletter 3:18-22.
PPI. 1998. Effects of potassium on plant diseases. In Potassium for Agriculture, Potash & Phosphate Institute, Norcross, GA. pp 37-39.
PPI. 1999. Phosphorus nutrition improves plant disease resistance. In Phosphorus for Agriculture, Potash & Phosphate Institute, Norcross, GA. pp 26-27.
Sanogo, S. and X.B.Yang. 2001. Relation of sand content, pH, and potassium and phosphorus nutrition to the development of sudden death syndrome in soybean. Can. J. Plant Pathol. 23: 174–180.
Snyder, C.S., L.O. Ashlock, P. Tacker, and D. Widick. 1995. Chloride toxicity and potassium nutrition. Soybean Update, March, 1995. U. of Arkansas Coop. Extension Serv.

*Sr. Vice President PPI, Southeast Director PPI, President FAR, Brazil Director POTAFOS and Northcentral Director PPI, respectively.

Soybean Rust and Fertility.doc

NEW RESEARCH INITIATED FOR 2005

Several studies are being established for the 2005 growing season in response to this article. Plots are being set up to have various nutrient treatments in place, appropriate for the respective area, in case the Asian rust becomes a factor during this season. Even if no rust problem occurs, these studies will provide valuable information on nutrient effects on soybean growth and effects on other diseases that may be present. Following are some brief highlights, which will be updated as the season progresses:

Plots are being established in Louisiana, Arkansas, Illinois, Missouri, Indiana, and South Dakota. Additional sites may be added if additional funding can be obtained. at this point, support is being provided by the Foundation for Agronomic Research, the Potash & Phosphate Institute, the Illinois Soybean Program Operating Board, Mosaic Company, Brandt Consolidated, U.S. Borax, and Illini FS. Contributions from other sponsors would be appreciated. Contact us for details.




Locations of FAR-PPI Nutrient x Soybean Rust Studies for 2005. Background shading shows primary soybean production areas; green areas have been scouted for rust; red ares are confirmed sites of overwintering rust.

ILLINOIS. A set of experiments is being established on the Eric Rund farm, Pesotum, Illinois, where strip-till application of various combinations of KCl, MAP, and MnSO4 was completed on April 8. Foliar B and fungicide will be applied to the crop during the growing season.

The application unit pictured below was used to apply the fertilizer in a band approximately 5" below the surface. The soybeans will be planted in the rows directly above the fertilizer band. We would like to acknowledge Dan Schaefer, Illini FS, Tolono, Illinois, the fertilizer dealer and Certified Crop Adviser cooperating in this study.


Soil samples were collected at 6" increments to a depth of 2 feet to characterize the nutrient supplying power of the soil. Samples were collected with a hybraulic probe, 15 cores per sample, and logged by GPS coordinates. Each core was divided into 6' inch subsample, then the 15 cores at each depth were composited.




A complete nutrient analysis will be run on each sample to characterize the plots at the beginning of the experiments. This deep prairie soil is known for its good nutrient supply, but in many field, the P and K levels decline dramatically below the 12" depth, so we felt it was important to look at the nutrients by depth through the major portion of the root zone.


More information will be posted on this website as the other plots are established and the season progresses.

Additional plots in Illinois will be established at two southern Illinois locations....Dixon Springs and Brownstown...under the direction of Dr. Steve Ebelhar. Details of these studies will be added to this site when the plots are in place.

INDIANA. A study in central Indiana is being coordinated by Dr. Shawn Conley (Purdue) and Certified Crop Adviser, Lance Murrell, in cooperation with PPI Northcentral Director, Dr. Scott Murrell, and Purdue Plant Pathologist, Dr. Don Huber. These plots are set up for soil applied KCl (potash) preplant, and foliar micronutrient application during the growing season.

LOUISIANA. Dr. Ray Schneider, Louisiana State University (LSU, will direct studies at the LSU research farm and on a cooperator's farm. PPI Southeast and Midsouth Director, Dr. Cliff Snyder will oversee these studies.

ARKANSAS.

MISSOURI. An existing soybena nutrition study in Missouri will be modified to study effects on Asian soybean rust. Dr. David Dunn will manage this project.

SOUTH DAKOTA.

 

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