Plant Physiol. (1971) 48, 457-460
Growth and Nutrient Uptake by Soybean Plants in,Nutrient
Solutions of Graded Concentrations
Received for publication March 12, 1971
JAMES E. LEGGETr1
Mineral Nutrition Laboratory
MAURICE H. FRERE
United States Soils Laboratory, Soil and Water Conservation Research Division, Agriculture Research Service,
United States Department of Agriculture, Beltsville, Maryland 20705
Soybean plants (Glycine max L. Merr. var. Hawkeye), grown
in nutrient solutions maintained
showed a large response in both shoot dry weight and total
ion uptake. Growth rate was dependent upon nutrient concen-
tration, even when quantity of nutrient was not limiting. Peak
periods for absorption of specific ions at eertain growth stages
were not exhibited. Rates of ion uptake by soybeans were
generally proportional to the growth rate during the period of
major growth. It is suggested that a dilute nutrient solution
could provide sufficient nutrients for adequate root growth
prior to major shoot growth, at which time a more concentrated
nutrient solution is needed.
at graded concentrations
mineral nutrition is poorly understood. One would suspect that
the nutrient uptake pattern of the whole plant would change
with different stages of growth because the nutrient contents of
the roots, stems, leaves, and fruit are all different. A compre-
hensive study (4) that combines years of field experiments indi-
cates that potassium uptake peaks when the beans start filling.
It is possible that other peak uptake periods were obscured
by a variable nutrient supply.
Not only is the concentration of the nutrient supply impor-
tant, but the ratios of the nutrients also modify the uptake pat-
tern in most plants (1, 3, 9, 10). The number of treatments
necessary to study both the concentration and ratio of nutrients
is beyond the scope of this study. Therefore, the ratio of
nutrients in the popular Hoagland's solution No. 1 (5) was
chosen as a beginning point. The experiments reported in this
paper were conducted to determine the nutrient uptake at va-
rious times during the growth cycle of soybeans supplied with
graded concentrations of nutrients.
Research on plant nutrition generally falls into two classes.
Most laboratory experiments have been short term excised root
studies to examine the kinetics of the initial uptake processes
(6, 7). Most greenhouse and field experiments have been more
concerned with the final yield and plant composition than with
the uptake patterns during the season. However, the needs of
today require us to manage our crop systems not only to obtain
maximum yield and nutrient use efficiency, but to do it with a
minimum of environmental pollution by excessive fertilizer
Successful management requires the supplying of the cor-
rect amount of nutrients to the plants at a time when they can
best use them. This means we need basic plant physiological
knowledge on the nutrient requirements of plants at various
stages of growth. Loneragan (8) has discussed the confusion in
the use of the term "nutrient requirement." It has been used to
describe the concentration of nutrients in the solution in which
the plant is growing and also the nutrient content of the plant
at optimum growth. Whereas our primary interest is in de-
termining the minimum solution concentration of a nutrient
that permits maximum yield, the nutrient content of the plant
is important in understanding the response of the plant to dif-
ferent nutrient levels.
The soybean was chosen as the experimental plant. It is
considered to be one of the most important crops, yet its
IPresent address: Department
of Agronomy, University of
MATERIALS AND METHODS
Soybean seeds (Glycine max L. Merr. var. Hawkeye) were
germinated by soaking in aerated distilled water for 6 hr fol-
lowed by placement between moist paper towels. The radicle
usually attained a 1-cm length by the end of 30 hr. For each
treatment, six seedlings were selected for uniformity of radicle
length and placed on cheesecloth stretched over the open
bottom of a No. 10 plastic stopper. Seedlings were covered
with moist filter paper and a watch glass until the roots pro-
truded through the cheesecloth into 1 liter of nutrient solution.
Nutrient solutions were the No. 1 Hoagland solution (5)
and the one-tenth, one-fourth, one-half, and three-fourth
dilutions. Full strength of this solution has the following com-
position of major nutrients: 1 mm KH2PO4, 5 mm KNO3, 5 mm
Ca(NO.)2, and 2 mm MgSO4. This is a little higher concentration
than used in another nutrient study (9). The micronutrients
were held constant for all variations in the above solutions.
These were added as follows: 5 pM B, 0.9juMMn, 0.8pMZn,
0.03ALMCu, 0.01 ,um Mo. Iron was added as ferric EDTA to a
level of 0.9 ,uM Fe. These levels are one-tenth of the recom-
mended Hoagland solution, because a full strength of this
solution resulted in toxic symptoms in preliminary experiments.
There was no evidence that the levels used were not adequate.
Soybean plants were placed in the various solutions after
germination between moist paper towels.
changed at least once daily to prevent more than a 10%
change in concentration. In some cases, when the growth rate
was high, 4-liter containers were used. The pH remained within
0.3 unit of the initial value of 5.5. The light chamber was on a
LEGGETT AND FRERE
15-hr day at a light intensity of 2000 ft-c. The temperature of
the chamber was maintained at 27 ± 2 C day and night.
Each treatment was replicated four times. This gaver yield
and total uptake data that were within ±12% of the mean.
Fios. 1, 2, 3, and 4. Soybean shoot growth and nutrient com-
position with time in four levels ofHoagland's solution.
Values reported in the graphs are averages of the four repli-
The treatment period was terminated by removing all six
plants from a container and separating the shoot and root at
the transition zone. Roots were rinsed four times with distilled
water to remove the nutrient solution. Shoots and roots were
transferred to paper bags and placed in a 60 C oven for 24
hr. This dry weight was used to express the plant yield for a
particular treatment. The dried samples were ground in aWiley
mill topass a 20-mesh screen.
Inorganic cation analysis was completed on plant material
after it was heated in a muffle oven to 480 C for 2 hr. The ash
was dissolved in 20 ml of 0.1 N HNO. and 10% acetic acid
solution. Cation content was determined by atomic absorption
Total nitrogen, determined by the Kjeldahl procedure, was
used as a measure of nitrate uptake since nitrate was the only
Attempts to grow plants in a full strength Hoagland solution
were not successful. Plants in this solution appeared to grow
normally for the first 10 to 14 days, but at the 18th day their
internodal length was relatively shorter than plants growing
in other solutions and their leaves were yellow. On the 25th
day when the lower leaves had begun to drop and a general
yellowing of the entire plant occurred, this treatment was dis-
continued. Some plants recovered from these symptoms when
the solution concentration was reduced.
The data are presented as the milliequivalents of nutrient
ions in the shoot (Figs. 1-4) or roots (Fig. 5) per single plant
during the growth period. Dry matter production is found
from the right ordinate for the identical growth period.
Plants grew relatively slowly at first, and sufficient plant
Plant Physiol. Vol. 48, 1971
GROWTH AND NUTRIENT UPTAKE BY SOYBEAN PLANTS
material for chemical analysis was not available until the 14th
day. The nutrient concentrations of dry shoots at this time are
given in Table I. There were only small differences in the
growth of the plants in the different solutions up to 30 days.
At this time the shoot growth in the half-strength solution be-
came exponential and produced the maximum growth. The
concentrations of nutrients in the plants in the different solu-
tions changed somewhat until the 30th day, after which they
remained essentially constant at the levels given in Table I.
Half or more of the growth in all the treatments occurred
while the nutrient concentrations in the plant remained con-
stant. This means that nutrient uptake is closely connected to
growth during much of the season.
The less than exponential growth of the plants in the solu-
tions other than the half-strength is considered to be the result
of nutritional stress. The soybeans must have been sensitive to
the salt level in the three-fourths strength solution, although
there were no visual symptoms. The response of the plants in
the tenth- and quarter-strength solutions confirms the generally
held hypothesis that the concentration as well as the capacity
of the solution to supply nutrients is important in the nutrition
While the shape of the growth curve was greatly affected by
the concentration of the nutrient solution, the stages of phys-
iological development occurred at about the same time for all
plants. For example, the first trifoliolate leaf was unrolled by
the 15th day. The plants began to bloom by the 25th day with
pod development following in a few days. Beans were filling the
pods at the last harvest. The greatly shortened time scale for
plant development compared to other studies (4, 9) is con-
sidered to be the result of the light and temperature regime
Nutrient solution concentration affected the shoot growth
and nutrient content of the shoot but not of the roots. The
growth and uptake by all roots were similar and are represented
by one set of data in Figure 5. The greatest root growth did
Table I. The Nutrient Concentrations in Soybeani Shoots Grown in
Four Dilutions ofHoagland's Solution at the First Trifoliolate
LeafStage and Averagedfor the Stages After the Start of
First trifoliolate leaf stage (14 days)
Averaged for the stages after pod for-
mation (30-43 days)
position with time in a nutrient solution.
Representative soybean root growth and nutrient com-
occur in the half-strength solution, but the final dry weight was
only about 50% larger than that for roots in the other solu-
tions. The scatter of the data prevents a clear-cut pattern, but
it is reasonable to expect the root system to reach some maxi-
mum size and then level off. The data from these experiments
suggest that this occurred between 28 and 35 days under the
conditions of this experiment.
The growth and nutrient composition of the aerial parts of
plants depend upon several environmental factors. We at-
tempted to keep constant most of these factors, including the
ratio of the major nutrients. Without frequent changes of the
0 Gro. th
3 SOILt "on
LEGGETT AND FRERE
nutrient solution, both the concentration and ratio of nutri-
ents change with time.
Although the plants were exposed to an unlimited nutrient
supply, the cells did not accumulate these ions to unusual
levels. This is in agreement with the findings of de Wit et al.
(10), who observed that plants grow at a rate correlated with
the plant organic acid level established to balance the excess
cation content. The growth and nutrient composition of the
plants grown on the one-fourth and three fourths-strength
solutions were similar. In addition the 4-fold increase in
growth by the plants in the one-half-strength solution was ac-
companied by a major change only in the potassium content.
In general, nitrogen concentration in the plants was affected by
the solution strength much more than the cation constituents.
However, in all cases it was much larger than the sum of the
measured cations (Table I).
The accumulation of nitrogen, potassium, and calcium by
roots is proportional to growth and constant concentrations of
about 2.9 meq N, 1.3 meq K, and 0.24 meq Ca per gram of dry
roots are maintained. Magnesium concentrations of the roots
decreased from 1.1 meq/g at 14 days to 0.7 meq/g in the
mature root. This is still much larger than the concentrations
in the shoot (0.2-0.3 meq/g).
The similarity of root growth and uptake over the 7.5-fold
nutrient concentration range indicates that meeting the root
requirements is not sufficient for maximum shoot growth. In
fact, a solution maintained at one-tenth strength might be
sufficient for the roots. The root-shoot interrelations can be
further illustrated by noting that the major increase in the
shoot growth in the one-half strength solution occurred after
30 days. A full root system is apparently needed to support
the rapid shoot growth.
It was anticipated that a larger demand for a particular
nutrient at some stage of growth would be reflected in an inflec-
tion point on the uptake curve for that nutrient. Such an in-
flection point is not obvious in the data. At the final harvest,
the beans were already formed and were filling the pods. After
this stage of growth, a decreased rate of uptake is expected as
the plant matures.
The data in Table I show that the concentration of potassium
in the plants growing in the optimum half-strength solution in-
creased after the first trifoliolate leaf stage whereas the potas-
sium concentration of plants growing in other solutions de-
creased. Evidently plants under optimum conditions have a
demand for potassium above that required for growth up to
30 days. This is understandable since it has been postulated
(3) that potassium cycles between the nitrate translocated up-
ward and organic acids translocated downward.
A most important time in soybean development appears to
be the start of pod formation. This occurred at about 30 days in
these experiments. Soon thereafter (36 days) roots ceased grow-
ing, although the rate of shoot growth was accelerating, and
the nutrient concentrations in the root reached a plateau.
These experiments suggest the following developmental
and nutritional questions that have important practical impli-
cations. Does root growth reach its maximum before the
exponential stage of shoot growth? If so, can adequate root
growth be obtained with lower nutrient concentrations than
those required for the later optimum shoot growth? Perhaps
the ratio of cations would have to be adjusted to favor
magnesium over calcium during this period. The practical
implication is that in the farming situation nitrogen fertilizers
may be leached away from the roots before the plants can
make best use of them.
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Physiol. 16: 691-720.
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and magnesium in soils by atomic absorption spectrophotometry. Analyst
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of the plant. In: Brit. Ecol. Soc. Symp. No. 9, Ecological Aspects of Min-
eral Nutrition of Plants. pp. 201-213.
4. HANWAY, J. J. AND H. E. THOMPSON. 1967. How a soybean plant develops. Spe-
cial Report No. 53, Iowa State University, Ames.
5. HOAGLAND, D. R. AND D. I. ARNON. 1950. The water culture method for grow-
ing plants without soil. Calif. Agr. Exp. Sta. Cir. 347.
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9. WEIGEL, R. C. 1970. Mineral nutrition of soybeans. Ph.D. thesis, University
of Maryland, College Park.
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