Diagnosing Nutrient Deficiencies in Mississippi Soybeans

Bobby Golden, Agronomist, Delta REC, Mississippi State University
By Bobby Golden, Agronomist, Delta REC, Mississippi State University June 14, 2014 18:25

Diagnosing Nutrient Deficiencies in Mississippi Soybeans

Diagnosing nutrient deficiencies is not rocket science, but can be cumbersome.  Many nutrient related issues occur early in season and can sometimes mimic herbicide injury in appearance.  In many instances it is difficult to tell the two apart. Most often nutrition related issues can be confirmed with a properly taken tissue test and corrected with an in season fertilizer application.  Fertilizer is expensive and most in season applications will be conducted via airplane that brings about an added application expense.  Therefore properly identifying nutrient issues is paramount in minimizing production costs.  Below are some keys to identifying nutrient related symptoms in soybean fields.

Potassium Deficient Soybean – A 60 bu ac-1 soybean crop will remove approximately 72 lb K2O ac-1 making soybean one of the crops that transports the most K2O away from the field in the grain. To properly diagnose K deficient soybeans we can key on a few items.  1) Potassium Deficiencies will generally occur in lighter textured soils (lower CEC). 2) Potassium is a mobile nutrient in the plant.  This means that most potassium deficiencies will show up on the lower leaves first, especially when observed early in the season. 3)  Classic symptomology for K deficiency is a chlorosis along the outer edge of the leaf tissue.

Potassium deficient soybean plant.

Potassium deficient soybean plant.

Late-season potassium deficient soybean plants.

Late-season potassium deficient soybean plants.

Phosphorus Deficient Soybean – Phosphorus deficiency is not as clear cut and easily identifiable as K in soybean tissue. Soybeans remove less P2O5 in grain when compared to K removed, but still remove an equivalent of 100 lbs Triple Super Phosphate or Diammonium Phosphate when producing a 60 bu per acre crop.  Phosphorus is also mobile in plant tissue, which means like K as new leaves develop they will borrow P from older leaves to keep the young growth healthy.  The older plant tissue then produces the symptomology.  A soybean deficient in phosphorus will generally appear spindly, with smaller leaflets (leaves will appear more rounded and look like peanut leaves) and have a stunted growth habit.  In some cases P deficient soybean will give the appearance of having a dark green to almost blue appearance.  Leaf tissue testing is the best method to accurately diagnose P deficiency.

Phosphorous deficient soybean plants.

Phosphorous deficient soybean plants.

 

 

 

 

 

 

 

 

 

Sulfur Deficient Soybean – Sulfur is a secondary nutrient, but is generally removed in a greater quantity than what is supplied to the soybean crop in Mississippi. A 60 bu per acre soybean crop will remove 11 lb S per acre when the grain truck leaves the turn row.  Sulfur deficiency most often occurs in Mississippi soybeans that are seeded to lighter textured, low organic matter soils (lower CEC) and sandy ridges within a field.  For many years we need not worry about S fertilization, but with the clean air act, much of the free S we used to get from atmospheric deposition has ceased.  Over the last 15 years with our shift to a more grain based system in the Delta, S deficiencies are starting to be observed.  Sulfur is immobile in the plant therefore soybeans will show S deficiency in the upper canopy, and will generally manifest in an overall yellowing or off green color in young leaves and buds.  Soybeans respond well to S application with S application improving yield and quality in deficient stands.  For immediate response, use a S product containing S in the form of SO4.

Sulfur deficient soybean plants.

Sulfur deficient soybean plants.

Sulfur deficient soybean plants.

Healthy soybean plants for sulfur comparison

Manganese Deficient Soybean – Manganese is a micronutrient required in small quantities by the soybean plant.  Manganese is an enzyme activator and is essential for proper root growth.  Deficiencies most often occur on high pH soils.  In Mississippi we have observed Mn deficiency on many of our heavy soils with pH greater than 7.0.  Unlike P and K, Mn is immobile in the plant.  This means that symptomology will most likely appear on the younger leaf tissue first, as Mn cannot easily be recycled from the older plant tissue.  The characteristic symptoms for soybean include interveinal chlorosis while the veins will remain dark green in color.  There may be varying shades of chlorosis across a field landscape.

Mangenese deficient soybean plants.

Mangenese deficient soybean plants.

Large area in a field with manganese deficient soybean plants.

Large area in a field with manganese deficient soybean plants.

Iron Chlorosis – In general, we observe very little Fe chlorosis in the Delta area of Mississippi, but it is an immense nutritional deficiency that is often observed in eastern Mississippi.  Unlike most nutrient deficiencies that occur because the element is lacking in the soil profile, there is generally an abundance of Fe in Mississippi soils. Iron chlorosis is caused by the inability of the plant to take up the Fe contained in the soil.  In eastern Mississippi the deficiency most often occurs when soil pH is greater 7.0 and free carbonates are present in the soil.  Oftentimes high soil NO3-N can amplify Fe chlorosis.  Fe chlorosis takes a program approach to help manage that included variety selection, limiting residual N fertilizer from previous crops, and infurrow applications of Fe chelates.

Severe iron chlorosis.

Severe iron chlorosis.

Iron chlorosis symptoms on soybean plants.

Iron chlorosis symptoms on soybean plants.

Nodulation Issues/ N Deficient Soybeans – Poor soybean nodulation can result in an N deficient soybean field.  Many characteristics are alternating areas of dark green and lighter green beans, which have very few if any nodules on lateral roots.  There are a host of potential items that can reduce the function and/or amount of active nodules in a soybean crop.  New soybean fields with little history of production, freshly land leveled fields, highly compacted soils, soils containing an abundance of residual N, and prolonged saturated conditions can all lead to reduced nodule formation and/or activity.  Fields with reduced nodule activity will respond to N application; however, it is generally not economically feasible to try and produce a soybean crop with N fertilization alone due to the vast amount of N required.

A field of chlorotic soybean plants exhibiting poor nodulation.

A field of chlorotic soybean plants exhibiting poor nodulation.

Main stem nodulation.

Main stem nodulation.

 

 

 

 

 

 

 

 

Urea Burn on Soybean – Many producers are electing to top-dress soybeans with urea fertilizer to try to gain a yield advantage in the high yielding soybean environments in Mississippi.  We have a research project addressing this topic and will have preliminary data at years end.  In most instances we do not observe a visual response like we do with the cosmetic burn associated with topdressing corn with urea.  This year we have observed a few soybean fields that have exhibited urea burn.  To date the soybeans have emerged from the burn.  The characteristics of urea burn on soybean are similar to corn with scorched, bleached tissue along the leaf margins that may progress into interveinal water soaked dead tissue.

Close up of urea burn on soybean leaves.

Close up of urea burn on soybean leaves.

Urea burn on soybean leaves.

Urea burn on soybean leaves.

 

 

 

 

 

 

 

 

 

 

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Bobby Golden, Agronomist, Delta REC, Mississippi State University
By Bobby Golden, Agronomist, Delta REC, Mississippi State University June 14, 2014 18:25
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