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IV. The EUF Values Required for Optimal Plant Nutrition and Their Calculation
(Jankoviq and Nemeth, 1974; Nemeth and Harrach, 1974; Ndmeth, 1972, 1975,
1977; Nemeth and Forster, 1976). In this connection, reference should be
made to the several thousand results of 5-year field experiments conducted by the
Tulln Sugar Factory in Austria. These studies show, for example, a sugar beet
yield of 55 tons/ha or a sugar yield of 8-9 tons/ha can be obtained from a soil
with the following EUF-K and EUF-P values at 200 V and 20°C : 15-18 mg of K
per 100 g and 1.4-1.6 mg of P per 100 g (Nemeth, 1977). This sugar yield was
obtained at exchangeable K contents between 15 and 30 mg per 100 g of soil,
depending on the clay content and the type of clay. The lactate Pz05values with
maximum yields were between 12 and 24 mg per 100 g of soil. In contrast to
these values, the optimal values for EUF-K and EUF-P can be more precisely
determined, because these nutrients extracted at 200 V and 20°C are effectively
available. As the availability of nutrients extracted by lactate solutions or NH4
acetate solution, depending on soil prbperties, can be very different, the optimal
lactate values can vary within the above-mentioned wide range.
Investigations carried out over the last few years, moreover, revealed that high
yields (wheat, maize, sugar beet, etc.) can also be obtained at lower EUF-K and
EUF-P values, if the K and P amounts desorbed at 80°C and 400 V are high
(Jankoviq and Nemeth, 1979). It is, therefore, advisable to consider both the
EUF-K and EUF-P values obtained at 20°C and those obtained at 80°C. If the K
and P reserves desorbed at 80°C are low in comparison with the K and P values at
20"C, these reserves can be neglected. In such cases, the already mentioned
values of 15-18 mg of K per 100 g and 1.4-1.6 mg of P per 100 g should be
considered (for wheat and rice 10-12 mg of K per 100 g per 20 min will be
sufficient). If, however, the EUF-K reserves at 80°C exceed 5 mg per 100 g per
15 min and the Preserves are above 1.0 mg per 100 g per 15 min, then 8-10 mg
of K and 1.0 mg of P per 100 g at 20°C are sufficiently high. The higher the
reserves are at 80"C, therefore, the lower the values at 20°C can be to ensure
optimal plant nutrition. The effectively available amounts at 20°C should not be
too low, however, as in that case an adequate supply of nutrients to the plant
roots will not be guaranteed despite high reserves.
1 . Calculation of the Amount of K Fertilizer
The K requirements depend on the quantity of clay minerals that bind K more
selectively in the soil than other cations as, for example, Ca, Mg, and Na. Soils
with low K selectivity-light soils, kaolinitic soils in tropical regions, and soils
with low pH values-release K very quickly by means of EUF (within 10- 15 rnin
at 20°C). Therefore, the EUFI fraction (0-10 min) is at least three times the
EUFIIlfraction (30-35 min). Often this third fraction is altogether missing (Fig.
13, oxisol). In this case there is no K fixation. If the soil adsorbs K selectively,
the K release by means of EUF at 20°C is very low. The course of the K-EUF
curve is correspondingly flat. Considerable amounts of K are still released within
EUF DETERMINATION OF SOIL NUTRIENTS
30-35 min, as compared with the EUF, fraction (Fig. 13, gray-brown luvisol, pH
The relationships between the amounts of EUFl and EUFlll and between the
amounts of E m - K at 20°C and EUF-K at 80°C for these soils are as follows:
EUF,:EUFII, = I: 1 or 2: 1
EUF-K (2O"C):EUF-K (80°C) = 1:1 or 1 : l
Most soils developed from sediments (for example, of loess) belong to this
group. Consequently, the soils can be classified by means of EUF into two
categories according to their K adsorbing power: (a) no K fixation, and (6)possibility of K fixation (selective binding). This is, however, only a qualitative
classification. In the case of K fixation, the amount of K fertilizer in kilograms
per hectare has to be determined. It is, therefore, necessary to ascertain the
relationship between the amounts of fertilizers and the amounts of nutrients
extracted by EUF for given soil properties.
The influence of soil properties on fertilizer nutrients has been studied in
numerous field, pot, and laboratory experiments. As a result, tables have been
drawn up that show the amounts of fertilizer in kilograms per hectare that should
be applied, so that the given amounts of nutrients extracted by EUF will increase
by a determined value (for example, by 1 mg per 100 g of soil) (Table Vn).
Quantity of K Required To Raise the EUF-K Value to
15 mg per 100 g of Soil
K requirements (kg/ha)
Value found in
Clay content (96)
. 5 . 9
K supplied by the soil (buffering)
Example. Soil test results from samples taken in July revealed an EUF-K rate
of 10 mg of K per 100 g per 20 min at 20°C. The rate for the following year was
fixed at 15 mg of K per 100 g per 20 min at 20°C. Question: How many
kilograms of K fertilizer have to be applied per hectare to obtain 15 mg of K per
100 g of soil? The amount of K fertilizer to be applied depends on the amount of
clay minerals that bind K selectively. If less than 10%of these clay minerals are
present in the soil, 190 kg/ha will have to be applied. Soils with a clay content of
3040% require 300 kgha. When only 13 mg instead of 15 mg is envisaged for a
soil with a clay content of 30% (high amount of K at 80"C), the K requirements
according to Table VII will be 300 - 90 = 210 kg/ha. The amount of 90 kg/ha,
which is necessary to increase the rate of 13 mg of K to 15 mg per 100 g, has to
be deducted from the 300-kg K value. Table VII can be used to determine not
only the quantities of fertilizer K needed but also the K supplied by the soil
(buffering). If a sugar beet yield of 55 tons/ha (8-9 tons of sugar per hectare)
removes from the soil 450 kg of K per hectare, the EUF-K value will decrease
from 15 to 8-9 mg of K per 100 g in a soil with 30-40% clay of high K
selectivity, and to 3-4 mg of K per 100 g in a soil with less than 10% clay.
2 . Calculation of the Amount of P Fertilizer
The P requirements of a soil depend on the clay content (Table VIII) also.
Example. Soil test results from samples taken in July revealed an EUF-P rate
of 1 mg per 100 g per 20 min at 20°C. For the following year the expected value
Quantity of P Required to Raise the EUF-PValue to
1.6 mg per 100 g of SOU
P requirement (kg/ha)
Clay content (%)
P supplied by the soil
EUF DETERMINATION OF SOIL NUTRIENTS
Ustalf I India 1
,,' 7.5ppm Mn
E " .
_ _ _ _ - ---~
-__ _ - - --
. . , ,,'
Red rellct sorlfFRG)
p H : 4.5
Nr 529 (North Sumatra)
30.0 ppm Mn
Nr. 530 f North Sumatra)
amount of P fertiluation ( k g P l h a )
FIG. 15. Relationship between the EUF-P values at 200 V and 20°C and the amounts of P
fertilizers of soils with nearly equal clay content and pH.
for this soil was fixed at 1.4 mg of P per 100 g. Table VIII shows that, with a clay
content of lo%,P fertilizer has to be applied at a rate of 40 kg/ha in order to raise
the EUF-P value from 1.O mg to 1.4 mg of P per 100 g. Soils with a clay content
of 40% require 60 kg of P per hectare.
The higher the amounts of fertilizer required to increase the amounts of
EUF-P, the less will be the change of these EUF values in the course of the
vegetation period. The expected decline of the EUF values can, therefore, also be
read off from Table VIII-namely, from the bottom to the top.
Table VIII, however, is suitable only for the calculation of P requirements in
soils with pH values above 5.5 or with low Al, Fe, and Mn concentration in the
soil solution. For, the higher the Al, Fe, and Mn concentration in the soil
solution, the more P is fixed at nearly equal amounts of clay and pH values (Fig.
15). The EUF heavy metal fraction (Fig. 6) should, therefore, also be taken into
account for the determination of P requirements in acid soils.
B. CALCULATION OF PHYSIOLOGICAL LIME
The limited growth of plants on acid soils is caused not so much by the high
H+ ion concentration of the soil solution as by the toxic effect of Al, Fe, Mn, Zn,
etc. ions. The physiological lime requirement of a soil is, therefore, determined
by the need to reduce toxic concentrations of heavy metals. But in soil testing
practice liming recommendations are often based on the titration of both H+ and
AIS+,as well as other heavy metal ions. There is, however, a loose correlation
Ca 0 requirement ftlha)
day content I%1
FIG. 16. Quantity of CaO required to eliminate heavy metal toxicity.
between the soluble and easily desorbable heavy metal fraction and the lime
requirement (titration with base). The physiological lime requirement differs,
therefore, from the conventional lime requirement.
Because of the large number of liming experiments, a table has been worked
out showing the amounts of CaO (in kilograms per hectare) needed to eliminate
heavy metal toxicity. Here the clay content plays a decisive role. With increasing
clay content, increasing amounts of CaO or CaCO, must be applied to eliminate
the toxicity of a given quantity of EUF-Fe and EUF-Mn. Thus, only a small part
of the total desorbable heavy metal will be extracted by EUF. The higher the clay
content, the less heavy metal can be desorbed by EUF at a given time. Therefore,
with increasing clay content higher amounts of CaO must be given in order to
inactivate the heavy metals not extractable by EUF in 35 min. Since the clay
content also can be determined by means of EUF, Fig. 16 can be used to calculate the physiological lime requirement.
According to investigations by Nemeth (1976), toxic symptoms were found in
red clover when the EUF-Mn and EUF-Zn contents had reached 15 ppm in
different soil types. The yield of red clover in pot experiments had been decreased about 70% by 40 ppm of Mn and Zn. For EUF-Cu this toxi; limit was 4
ppm. These critical toxic values should be further investigated for plant species
and varieties in order to obtain detailed information on the necessity of liming
(Brown and Jones, 1977). In any case, optimum plant nutrition with
macronutrients-ca, K,and Mg-plays a decisive role (Vlamis, 1953; Nemeth
and Grimme, 1974; Nemeth, 1976).
EUF DETERMINATION OF SOIL NUTRIENTS
V. Conclusions for Practical Soil Analysis
Modem plant nutrition requires from soil analysis information on the concentration and composition of the soil solution and on the amount of effectively
available nutrients. It must further be ascertained to what extent the concentration
of nutrients in the solution is changed by removal of nutrients by the plants or by
the addition of definite amounts of fertilizer (fertilizer requirements).
Conventional soil analysis (single chemical extraction) can only partly fulfill
these requirements. If weak extraction agents are used (water, 0.025 M CaCI,,
etc.), approximate statements on the nutrient concentration in the soil solution
are possible, but it remains unknown how these concentrations are changed by
removal of the plants during the vegetation period. For instance, a certain amount
of K extracted with 0.025 M CaCl, may be associated with a sandy soil without
buffering, and the same amount with a heavy clay soil with high reserves. For the
same reason, it also cannot be stated to what extent these values determined by
weak extraction are altered by specific amounts of fertilizer. In a clay soil, such
changes would be much less than in a sandy soil. Nevertheless, these methods
are preferable to those that work with stronger extraction solutions (for example,
with acid or salt solutions). Larger amounts are extracted with the latter, but their
effective availability remains unknown. The correlations between the uptake of
the plants and the values of these soil analyses remain, therefore, unsatisfactory.
However, the great advantage of the rapid chemical methods is that they can be
performed easily and quickly. Their ease of performance in routine investigations, however, should not cause their importance to be overestimated. All
one-sidedness in soil analysis should be avoided, since it does not constitute
progress, but a step backward. Speed may be attained at the expense of gaining
If rapid chemical methods are to be retained in practical soil testing, the
analysis should be extended to other soil properties. The relationships between
the values obtained by chemical analysis (lactate values, exchangeable cations,
and the nutrient concentrations in the soil solution) and other soil properties (clay
content, type of clay, etc.) have been explored thoroughly. These relationships
enable a better interpretation of the values of conventional soil analysis. An
extended soil analysis covering clay content, kind of clay, nutrient fixation, etc.,
entails a considerable expenditure of time, work, and materials, however.
A further possibility is to develop methods in which these soil properties are
incorporated into the results of the analysis. This possibility is afforded by the
EUF technique. The quantity of effectively available nutrients is reproduced very
well at low voltages (50 and 200 V) and at 20°C. On the other hand, the rates of
desorption at 400 V and 80°C characterize the nutrient reserve.
The relationship between the effectively available fractions (0-20 min at 20°C)
and the reserves (at 80°C) can give information on important soil properties such
as clay content, type of clay, type of soil phosphate, and CaCO, content. Therefore, the fertilizer requirements (K, P, and CaO) of a soil can be determined by
means of EUF (Tables VII and VIII and Fig. 16).
The EUF values required for optimal plant nutrition can be determined more
precisely when the temperature and voltage are varied. If the reserves at 80°C are
high, the effectively available fraction can be lower. High reserves are,however,
of little use at low contents of effectively available nutrients, as an adequate
supply of nutrients to the roots will not be guaranteed.
Since soil analysis (whatever the method) determines only a few of the components of nutrient availability, there are limits to its prognostic value. Apart
from the amount of available nutrients that are measurable with EUF, the transport of nutrients to the plant roots, for instance, depends on the actual water
content of the soil and the average diffusion paths. The more intensively the soil
is penetrated by roots, the shorter is the average diffusion path.
In determining the nutrient requirements, the expected yield or yield potential
of the location-that is, higher possible yield-should be taken into account as
well as the nutrient supply. The yield potential depending on the physical properties of the soil can be characterized according to Harrach (1970) by the utilizable water capacity of the soil that can be penetrated by the roots. Wittman and
Grottenthaler ( 1975) demonstrated correlations between the ‘‘degree of ecological moisture” and the yield potential. The nutrient requirement for this yield
potential can be calculated by the EUF method.
In conclusion, it can be observed that nutrient extraction by means of the EUF
technique is very similar to the processes of nutrient supply to the roots that
actually take place in the soil. The technique is thus more universal in application
than the conventional methods are. It is suitable for very different types of soil,
including those in unknown locations, where the nutrient status and fertilizer
requirements can be only partly determined by the usual rapid methods (single
In principle the EUF technique can also be used for nutrient fractioning in
plant material and fertilizers. Furthermore, it can be applied successfully under
ecological aspects, since the solution rates of most of the toxic and useful substances in sewage sludge, compost, etc., can also be measured by EUF.
I am grateful to Prof. Dr. H. Beringer and Dr. H. G r i m e for their helpful suggestions. and to
Mrs. M. Labrenz and Mrs. I. Miihlhausen for assisting in the preparation of this manuscript.
Adams, P.,and Winsor, G.W. 1973. Plant Soil 39,649-659.
Barber, S.A. 1962. Soil Sci. 93, 39-42.