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record of the Institute for Food and
Agricultural Sciences and should be
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Copyright 2005, Board of Trustees, University
Homestead AREC Research Report SB74-5
Manganese Fertilization of Vegetable Crops in Dade County
Paul G. Orth/
Small amounts of manganese (Mn) are included in fertilizers applied to many vegetable
crops grown in Dade County. Sometimes questions are raised concerning whether Mn
in the fertilizer is necessary and, if it is, how much and what form should be
applied. This report is a summary of the information we have at the present time.
Plants need very little Mn to grow and to produce a crop at maximum potential. For
example, an acre of tomato plants may use only 1/2 pound of Mn per crop, but in Dade
County the fertilizer applied usually contains 20 Ib/A. This comparison illustrates
the inefficiency in fertilizing with Mn. Fertilization rates of other metallic micro-
nutrients and phosphorus often indicate similar inefficiencies. A brief discussion
of the chemistry of Mn in our high calcium carbonate (lime) soils will help in under-
standing the disproportionate application of Mn in relation to its actual utilization
by the crop.
Plants obtain Mn and other inorganic nutrients from a small supply dissolved in the
water in the soil. Part of this water along with the nutrients it contains is taken
up by plant roots. Only a small portion of all the nutrients in the soil is dissolved
in the soil water. For example, most of the Mn in the soil is there in solid form.
As additional water as rain or irrigation is added, the solid Mn compounds begin to
dissolve and replenish the supply in solution. The supply is replenished more rapidly
by the more soluble Mn compounds. Manganous sulfate (MnSO4), frequently used as a
fertilizer, is a very soluble form of Mn. When MnS04 is incorporated in the soil it
-changes to less soluble, less available, forms of Mn. Because the amount of Mn
needed in the soil solution is rather small, even slightly soluble compounds can re-
plenish Mn removed from the soil water. This replenishment is affected by a number
of factors in addition to solubility. The result of this complex situation is that
compounds such as manganous oxide (MnO) and manganese dioxide (MnO2) which are
generally considered insoluble can be effective fertilizers under some conditions.
Since soluble Mn compounds become less soluble when added to our calcareous soils,
Mn accumulates from repeated applications. Thus there is an increase in the reserves
of Mn in the soil which will supply at least a portion of a crop's Mn requirement.
In time the accumulated Mn in the soil may become adequate for crop growth and Mn
fertilizers may be omitted, reduced, or replaced by cheaper, less available forms to
maintain the Mn supply at the necessary level of availability. Soil analysis can be
used to measure changes in the Mn supply in the soil.
Sometimes Mn deficiency is influenced as much by the crop as by the supply in the
soil. For example, a period of rapid growth will increase the rate at which Mn is
removed from the soil. Also injury to the root system impairs the ability of the
plant to obtain nutrients. Thus, both the chemistry of the soil and the vigor of
the plant must be considered when evaluating the need for Mn fertilization.
Assistant Soils Chemist, Agricultural Research and Education Center, University
of Florida, IFAS, Homestead, Fla. 33030.
July 16, 1974
Manganese deficiency in potatoes and tomatoes grown on Perrine marl soil in Dade
County was studied as early as the 1920's. The major findings of various scientists
can be summarized briefly. Manganous sulfate is a very effective Mn fertilizer.
Rates from 10 to 50 lb. MnO equivalent/A give maximum growth and yield of potatoes
and tomatoes with 25 Ib./A usually sufficient. Manganous oxide sometimes gives as
good response as sulfate. Materials such as Mn02 and Mn chelate (MnEDTA) are ef-
fective only at much higher rates of application.
The accumulation of Mn was noted in fields repeatedly fertilized with Mn. Fifield
and Wolfe suggested Mn could be left out of the fertilizer for at least one year
after it had been applied for five years. Malcolm grew potatoes without added Mn for
four consecutive years without reduction in yield on land previously cropped for 15
years. On land previously cropped 4 to 5 years, tomato yield was increased in two
out of four years by 8% when Mn was included in the fertilizer. Leaves, in the fourth
year, contained 19 parts per million (PPM) Mn where no Mn had been applied recently
and 50 PPM where the 50 pound rate had been applied.
When vegetable crop production expanded to Rockdale soil, fertilization of these
crops with Mn continued. The usual material has been MnSO4 but interest in the use
of MnO has increased because there is a good supply of this material from commercial
sources, and the cost is less per unit of Mn than for the sulfate form.
Both Rockdale and Perrine soils contain large amounts of calcium carbonate (CaCO3).
Perrine marl is over 90% CaCO3 and of silt loam texture. Cultivated Rockdale soils
contain 25 to 75 percent rocks and gravel of oolitic limestone. The fines are domi-
nated by CaCO3 although some silica sand and clay are usually present also.
To update information on Mn fertilization two experiments with tomatoes were conducted
to compare MnO with MnSO4 on Rockdale soil. One was a field experiment on previously
cropped land with rates and placement compared in addition to source of Mn. Plants
were sampled once and leaves twice for Mn analysis. Yield of fruit was also measured.
The second was a pot experiment using Rockdale soil which probably had not been pre-
viously fertilized with Mn. Rates of Mn and two degrees of rockiness were compared
in addition to the two sources of Mn.
RESULTS AND DISCUSSION
In experiment I plots with no Mn fertilizer gave the greatest yield, but some MnO
and some MnSO4 treatments gave yields not significantly different. Plants from the
check plots had the lowest concentration of Mn in their leaves, 32 PPM, at the first
sampling and 2nd lowest at the second sampling. However, differences between treat-
ments were small. Thus both yield and tissue analyses showed the soil had an adequate
supply of Mn for that crop of tomatoes.
In experiment 2 the plant analysis data, table 1, show a significant response to Mn
treatment. However, plant growth was greatly variable in replicates, and differences
between treatments were not statistically significant.
t Manganese concentration in the tomato plant was significantly increased by 50 PPM of
In from MnSO,, treatments I and J, at all three samplings. The lower rate, treat-
ments G and H, and the high rate of MnO, treatments E and F, were only slightly
effective. Thus MnSOA was a more efficient source than MnO. An even higher rate of
MnO may have given a higher concentration of Mn in the plant.
Substitution of rocks for one-half the soil caused a significant reduction in Mn
concentration in plants containing the most Mn; compare treatment I with J. A
similar trend can be seen for the other treatments. This may be due to the restricted
rooting volume where rocks were used.
The data from these two experiments indicate that Rockdale soil responds similarly
to Perrine marl as far as Mn fertilization is concerned. That is, soil which has
been fertilized little with Mn is likely to require the application of fertilizer
containing Mn for maximum vegetable crop production, and MnS04 is more effective
than MnO. However, soil which has received many Mn applications in the past is likely
to have an adequate reserve of Mn, at least for one crop and possibly for several
crops. In addition, the application of fungicides containing Mn help prevent a
nutrient deficiency of Mn.
Since Mn has accumulated in cropped soil, less soluble Mn materials such as MnO may
be as effective as MnSO4 in maintaining the Mn fertility level of the soil.
Growers may want to evaluate in the field the need for routine applications of Mn.
Manganese can be left out of the fertilizer in one field or a part of a field, or
less expensive sources of Mn can be used in the fertilizer. If Mn deficiency symp-
toms are observed they are easily corrected with a MnSO4 spray. The soil tests for
Mn are effective in measuring Mn reserves, but data are needed to determine values
corresponding to deficient, adequate, and high for Perrine marl and Rockdale soils.
The extension agents with the help of research personnel can assist the grower in
evaluating the effect of changing the Mn fertilization program.
A brief discussion of some physical aspects of fertilizing with Mn is appropriate
here since a response seen in the field may be unrelated to the chemical reactions
taking place. Since Mn is applied in such small amounts, uniformity of application
may be a factor in results. The Mn must be distributed in the fertilizer as uniformly
as possible when the fertilizer flows out of the hopper on to the soil. This is
easily achieved if the Mn is added to the mix before granulating or if the granules
are coated with the Mn material. Both may not be feasible for economic reasons. If
the Mn fertilizer is blended with fertilizer granules, it should be as close to the
same particle size as possible in order to become and to remain uniformly distributed
in the mix. However, the disadvantage of granules over a powder in the soil is the
small surface area and thus greatly reduced availability to plants of slightly
soluble materials such as MnO and Mn02 when in granule form. When Mn is being used
only to maintain adequate reserves in the soil better uniformity may be achieved by
applying twice the annual application every other year.
(1) Rockdale and Perrine soils are deficient in Mn in their natural condition. A
rate of 25 Ibs. of MnO equivalent/A from MnSO4 is appropriate for such soils.
(2) Manganese applied in fertilizer accumulates in the soil, and after many years the
soils are not deficient in Mn. A grower can omit Mn from the fertilizer applied,
or he can use a less soluble, less expensive Mn fertilizer to maintain the level
built up in the soil. Which practice is better is not clear at this time.
(3) The Mn status of the soil can be evaluated by soil analysis, and the Mn status
Y of the crop can be evaluated by tissue analysis. Crops deficient in Mn can be
sprayed with a MnS04 solution.
Treatments and manganese concentration
* PPM Mn in media
** Numbers followed by the same letter are not significantly different at the 5% level, Duncan's Multiple
in tomato plants from experiment 2.
Rate* 3/25 4/2
0 36 a 33 a
0 49 ab 38 a
10 38 a 38 a
10 49 ab 36 a
50 41 a 41 a
50 54 ab 39 a
10 64 bc 46 a
10 70 c 51 a
50 122 d 89 b
50 141 e 105 c