Glyphosate and Micronutrients

The Kansas and Indiana studies found glyphosate resistant soybeans to be vulnerable to manganese deficiencies while non resistant varieties are not.

By Jim Halbeisen

"Missing Micronutrients," an article in the Spring 2007, edition of John Deere's The Furrow, is based on research by Don Huber, professor of botany and plant pathology at Purdue University and Barney Gordon, agronomist at Kansas State University.  These researchers claim "using glyphosate is complicating the uptake of some minor nutrients."

The Kansas and Indiana studies found glyphosate resistant soybeans to be vulnerable to manganese deficiencies while non resistant varieties are not.  Yield studies showed manganese additions to glyphosate resistant soybeans helped to erase "yield lag" (or "yield drag" as some call it).

The researchers offer several theories to explain the yield lag in glyphosate resistant soybeans: 

    1.  One explanation is that glyphosate was originally developed as a chelating agent, meaning its molecule wraps around the molecules of other elements making them unavailable.  Glyphosate applications on soybeans, for example, "tie-up" manganese causing "yellow flash" symptoms.

    2.  Another is reduced soil biological life is related to manganese deficiency.  Following plant application, glyphosate moves from the leaves to the roots, where it is then secreted into the root zone.  In the root zone, glyphosate reduces soil organism populations needed to make manganese available to the plant.  (Remember, many botany text books say soil microbes are "plants" which means they could be susceptible to glyphosate.)

    3.  The researchers believe the gene inserted into soybean seed to give it glyphosate resistance also influences its root environment by changing the composition of an exuded substance from the plant's roots that helps it solubilize and utilize soil manganese.  Thus, by changing the root exudate, the amount of manganese available to the soybean plant is reduced.

For years the chemical companies have said glyphosate applications have no residual effect to the soil.  However, Huber's and Gordon's research seems to cast different light on that claim.  But even though there might not be residual herbicide effects on crops planted after glyphosate applications, there still could be changes in the soil's life and environment. 

Also, for years Growers Chemical Corporation has said foliar feeding the minerals and nutrients found in GMS can have significant positive influences on soil microbes by way of the energy (sugar) gained by plants receiving GMS sprays.  Don M. Huber's research at Purdue University substantiates our position.

To overcome manganese deficiencies, Huber and Gordon believe soil applications of manganese are best.  When weeds are small (under 2 inches), they think any kind of manganese spray will work, but, as weeds grow larger, they suggest using a chelated form of manganese in the glyphosate spray.  (Growers would qualify here.)

Referring back into The Growers Solutions archives, in the Summer 1999 edition (volume 12 issue 3) we discussed the use of glyphosate in conjunction with Growers Mineral Solutions (GMS).  Although Growers Chemical Corporation does not recommend mixing any chemicals with GMS, we knew farmers were doing it, so we wanted to add words of caution.  (See shaded area)  Since that 1999 article we can add more from recent on farm experiences.

    1.  If using GMS with glyphosate, it is important the spray volume be adequate to cover the small weeds hidden under the plant canopy.

    2.  When highly diluting GMS with hard water, the  water must be correctly acidified to avoid chemical interactions.  (See The Growers Solution, Summer 2000, Vol. 13, Issue 3. for dealing with hard water situations.) (See second shaded area.)

    3.  GMS applied with the glyphosate has helped fight off yield lag, effected by the chelation elements in GMS and confirming what  The Furrow article suggested be used. 

    4.  Some GMS representatives have clients reduce their glyphosate rates when applying it with GMS, saying it helps keep the spray cost down, although weed species and infestation can influence this decision.  Others feel a lighter glyphosate rate is less harsh to the plant environment and will help increase yield.  The researchers in "Missing Micronutrients" seem to back up this idea with their discussion on soil microbes and plant exudates.

    5.  Some companies believe glyphosate works better when sprayed during the heat of the day, but our experience does not confirm this thought, especially when used with GMS.

Finally, Don Huber and Barney Gordon suggest manganese deficiencies not only affect soybeans, but also glyphosate resistant corn.  And, they contend manganese is not the only micronutrient element affected, but that zinc or iron absorption may also be impaired.  Anyone using glyphosate resistant soybean or corn plants for silage or hay can recognize and understand Huber's and Gordon's conclusions.  Namely, that manganese deficiencies cause yield reductions in glyphosate soybeans, and in significantly lower manganese concentrations in above ground plant parts.  This means it is possible to have lower levels of zinc and manganese in silage and hay crops which would affect the immune systems of the animals consuming them.

Many customers have found increased micronutrient levels in their silages and hays after foliage spraying them with GMS as recommended by their Growers representatives. 

Foliar spraying GMS might well be the best way to overcome the negatives of glyphosate sprays and their resistant gene insertions.


GMS has usually been recommended to be applied straight, or undiluted, for different reasons, one is that the water used for dilution could have complicating chemistry problems.  Likewise, because the water volumes recommended for glyphosate spray coverage, diluting water quality (hardness) must be considered when GMS is to be included in the spray. 

Below are pictures showing how water quality can affect the spray effectiveness of GMS.  Each of the three bottles has 10 parts water mixed with l part GMS. 




The bottle on the left has soft rain water (with dissolved solids readings of 0 - 20 µmhos, or 3 grains or less +/-) mixed with GMS, resulting in practically no nutrient precipitation and making most all the minerals in GMS available to the plants being sprayed.

The center bottle has semi-hard water (dissolved solids of 600 - 650 µmhos, or 12 - 15 grains +/-) mixed with GMS, resulting in some precipitation which indicates some of the minerals in GMS are "tied up," and will not be available to the plants being sprayed.

The right hand bottle has hard water (dissolved solids of 1500 - 1700 µmhos, or 70 - 75 grains +/-) mixed with GMS resulting in significant precipitation.  This indicates a large percentage of the GMS's beneficial minerals are "tied up," or not usable, seriously reducing the nutritional benefits intended for the plants being sprayed.

The water in the center and right hand bottles should be treated, acidified, or in someway, neutralized, so that the useful minerals in the GMS do not precipitate.


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