Effect of the potassium source, either as KNO3,
K2SO4 or KCl, in nutrient solutions on the growth
of sand-potted peach or apple nursery trees
1
ADVERTORIAL
S.A. Oosthuyse (right), 2D.R. Napier, and 3H.T. Holwerda
HortResearch SA, P.O. Box 3849, Tzaneen 0850, South Africa
1
SQM Africa, P.O.Box 705, North Riding 2162, South Africa
2
SQM Europe, Houtdok-Noordkaai 25a Antwerpen 2030, Belgium
3
Abstract
posed to KCl or K2SO4 in supplying fruit trees
teria in the soil. Conversion rate and the ex-
The benefit of using KNO3 as opposed to KCl
with potassium.
up a set of complete nutrient solutions was
Introduction
and the quantity and activity of the relevant
demonstrated. Nursery Golden Magic peach
Plants take up nutrients directly from or with
bacteria present (Zhu and Chen, 2002; Nor-
and Anna apple trees (Orion Nursery, We-
the water surrounding soil particles, between
ton and Stark, 2011). Soils comprising main-
stonaria, South Africa) were transplanted
which the roots and root hairs are embedded.
ly sand and very little organic matter, from
into 2.7 l pots containing river sand, and
This water is termed the soil solution. Only
which bacteria feed, are less conductive to
treated with one of three nutrient solutions.
specific chemical forms of nutrients are tak-
conversion than loams or clay soils with a
The solutions were made up using the same
en up. Nitrogen is taken up either as nitrate
relatively high organic matter content. Many
fertilizers except for those supplying potas-
(NO3) or ammonia (NH4+). Phosphorus is tak-
situations are known to not be conducive to
or K2SO4 as the potassium source in making
sium. The potassium source was KCl, K2SO4
or KNO3. As a consequence the ammonium to
The main determinants are soil temperature
en up as orthophosphate, being either HPO4-2
or H2PO4-. Potassium, calcium, magnesium,
nitrate ratio differed between solutions as well
copper, iron, manganese and zinc are taken
as the chloride or sulphate content. Elemental
up in cationic forms K+, Ca++, Mg++, Cu++,
content except for that of S and Cl was equal.
Fe++, Mn++, and Zn++, respectively. Sulphur is
Identical experiments were performed on each
taken up as the anion sulphate (SO4-2). Boron
fruit type. One new shoot was permitted to de-
is taken up as boric acid (H3BO3), which is
velop per tree after heading the trees back to
known as an extremely weak acid, dissociating
above the graft union. New shoot length was
little in water in relative terms. Molybdenum
measured weekly from mid- or late December,
is taken up as the anion molybdate (MoO4-2).
2013, until late January, 2014. On the last
The anion chloride (Cl-) is taken up readily
date of measurement, the new shoots were cut
even though it is generally only required in
from the trees, and number of leaves initiated
trace amounts. Cationic sodium (Na+) is also
and fresh and dry weight determined.
readily taken up, but is not an essential nutri-
Growth was most vigorous in the trees
tent of conversion depend on many factors.
ent in most crop plants. Certain types of C4
treated with the solution made up with KNO3.
plants are an exception. Soil or irrigation wa-
Vigour differences relating to KCl or K2SO4as
ter may be marginally or highly concentrated
the K source were not apparent. Leaf number
in NaCl. Excessive Na+ or Cl- uptake can be
per shoot, or shoot fresh or dry weight bore a
injurious, plants varying greatly in tolerance
direct relationship with shoot length. This sig-
to the presence of these ions.
nifies that differences in length were not solely
Nutrient solutions or nutrient applica-
due to differences in the extent of inter-node
tions are made-up or made using available
Fig. 1 Anna apple (top) and Golden Magic
extension, and also occurred as a result of
fertilizers, which are crystalline salts of vari-
peach (bottom) nursery trees after transplant-
differences in dry matter accumulation. The
ous forms. It is noteworthy that applied NH4+
ing in 2.7 l pots containing river sand. One
results indicate a benefit in using KNO3 as op-
may be converted to NO3 by nitrifying bac-
TECHNOLOGY
49
AUG | SEPT 2014
shoot was permitted to develop per tree.
ADVERTORIAL
Fig. 2 1 000 l tanks in which the nutrient solutions were made up.
nitrification. Soil colloids, namely clay parti-
tilizer mixes or made-up solutions is for the
al., 1971; Ragab, 1980; Van Beusichem et al.,
cles and stable organic molecules, buffer nu-
most part tailored to be highest. In consider-
1987), including Cl- (Guohua, et al., 2000).
trient salt levels in the soil solution. Buffering
ing different solutions with respect to nutri-
This is essentially due to electroneutrality
capacity is imparted by small size and surface
ent ion constitution made up to contain the
charge. The density of negative charge far
same quantities of plant-essential elements,
having to be maintained endogenously. NO3-
exceeds that of positive charge, and hence
the NO3 to NH4 ratio of solutions made
cationic nutrient salts are mainly buffered
following their uptake by plant roots. Due to
-
+
uptake as opposed to NH4+ uptake, is thus associated with promoted uptake of a greater
up with KNO3 will exceed that of solutions
abundance of nutrient ions, as well as those
required in greater quantities. Furthermore,
pronounced differences in clay and organic
made up with KCl or K2SO4. Moreover, solu-
tions made up with KCl will inevitably con-
reduced Cl- sensitivity is implicated when
matter composition between soils, buffering
tain more Cl- and solutions made up with
and nitrification capacity correspondingly
K2SO4, more SO4 .
Cl- is present. It may be concluded that NO3-
differ widely.
rich solutions effect enhanced growth when
-2
Plants have a relatively high uptake affin-
In made-up nutrient solutions or the soil
solution, the number of anions present will
ity for NO3- or NH4+ due to their relatively
high need for N. Increased NO3 uptake is
-
compared with NH4+ rich solutions. Solu-
tions made up with KNO3, as compared with
K2SO4 or KCl, giving rise to an abundance
always equal the number of cations present.
associated with increased nutrient cation
Ion mixes can, however, differ vastly in con-
uptake (Cunningham, 1964; Jackson and
stitution. Of consideration mainly are differ-
Williams, 1968; Kafkafi et al., 1971; Blevins
eration is changes in ion concentration when
ences in the NH4+ to NO3- ratio as influenced
et al., 1974; Ernest and Knight, 1977; Frost
root uptake takes place. When NO3- is abun-
of NO3- relative to NH4+, should thus result
in more vigorous growth. Another consid-
by the potassium source used, either being
et al., 1978), the promotion of Na uptake
KCl, K2SO4 or KNO3 in agriculture. Nitro-
and the exclusion of Cl uptake (Guohua, et
be expected to be greater than when excess
soil derived elements of most if not all crop
al., 2000), whereas increased uptake of NH4+
is associated with increased uptake of nutri-
NH4+ is present; this resulting from the en-
hanced removal of nutrients salts. Reduced
plants, and hence, their constitution in fer-
ent anions (Cunningham, 1964; Kafkafi et
salinity stress is thus implied in solutions
gen and potassium are the most utilized
+
-
dant, the ion concentration reduction can
Table 1 Fertilizer quantities and molar concentrations of each solution. Shading indicates where differences in concentration or K source existed.
Solution K1 - /1000 l tank
g
Ammonium sulphate
452.0
mmol/l
Solution K2 - /1000 l tank
3.42
Ammonium sulphate
g
452.0
mmol/l
Solution K3 - /1000 l tank
3.42
Ammonium sulphate
g
mmol/l
114.5
0.87
MAP
125.0
1.09
MAP
125.0
1.09
MAP
125.0
1.09
Potassium chloride
409.4
5.49
Potassium sulphate
509.1
2.92
Potassium nitrate
545.0
5.39
Magnesium sulphate
150.0
150.0
150.0
EDTA Cu
EDDHA Fe
0.59
Magnesium sulphate
2.2
0.006
EDTA Cu
25.1
0.058
EDDHA Fe
0.59
Magnesium sulphate
2.2
0.006
EDTA Cu
25.1
0.058
EDDHA Fe
0.59
2.2
0.006
25.1
0.058
EDTA Mn
4.9
0.013
EDTA Mn
4.9
0.013
EDTA Mn
4.9
0.013
EDTA Zn
6.4
0.015
EDTA Zn
6.4
0.015
EDTA Zn
6.4
0.015
Sodium borate
3.3
0.008
Sodium Borate
3.3
0.008
Sodium Borate
3.3
0.008
Sodium molybdate
0.1
0.0004
Sodium molybdate
0.1
0.0004
Sodium molybdate
0.1
0.0004
0.93
Calcium nitrate
0.93
Calcium nitrate
Calcium nitrate
200.0
pH
EC (dS/m)
200.0
4.33
1.9
TEGNOLOGIE
200.0
0.93
pH
4.45
pH
5.34
EC (dS/m)
2.06
EC (dS/m)
1.32
50
AUG | SEPT 2014
Fig. 2 New shoot lengths of peach (left) or apple (right) on each of the dates of measurement. The trees had been headed back to above the graft
union, one new shoot having been permitted to develop per tree.
greater in NO3- than NH4+.
The trees were planted in 2.7 l plastic pots el-
each pot after each irrigation. The trees were
In the present study, differences in vig-
evated above the ground and containing river
sprayed weekly with malathion and tebu-
our of apple or peach nursery trees potted in
sand in a nursery enclosed with 40% shade-
conazole to prevent insect and fungus attack.
river sand was assessed in relation to solution
cloth (Fig. 1). Nutrient solutions were made
One new shoot was allowed to develop from
nutrient-ion composition, the solutions hav-
up in 1 000 liter tanks (Fig. 2). The fertilizers
each after all had been headed above the
ing been made up with either KNO3, KCl or
used, the elemental content per 1 000 l, the fer-
graft union (Dec. 2, 2913). Unwanted later-
tilizer molar concentrations, and the NH4 to
als were pinched off shortly after they began
K2SO4.
+
NO3- ratio of each solution are shown in Ta-
developing. In peach, new shoot length was
bles 1 or 2. The solutions differed concerning
recorded weekly from Dec. 18, 2013, to Jan.
Sixty grafted Anna apple trees and 60 grafted
ammonium sulphate input, the potassium
29, 2014. In apple, new shoot length was re-
Golden Magic (C75/21) peach trees were ob-
source used, and Cl- and SO4-2 content.
corded weekly from Dec. 27, 2013, to Jan. 27
burg, South Africa. Identical experiments were
Each pot received 300 ml of one of the solu-
on the last day of measuring, and the fresh
carried out in each fruit type. In each the fol-
tions on Monday, Wednesday and Friday of
weight and number of leaves on each imme-
lowing was performed:
each week, application commencing on Dec.
diately recorded. They were then placed in
2, 2013. 90 to 120 ml of solution drained from
brown paper bags and left to dry to crispness
Materials and Methods
tained from Orion Nursery south of Johannes-
2014. The new shoots were cut from the trees
Table 2 Elemental content (g) of each nutrient in each 1 000 l tank. Differences occurred in the S and Cl content.
The ammonium (NH4+) to nitrate (NO3-) ratio of each solution is presented.
Potassium Chloride - K1
N
P
K
Ca
Mg
S
Cu
Fe
Mn
Zn
B
Mo
Cl
Na
148.9
33.3
208.8
31.0
15.0
128.0
0.33
1.51
0.64
0.96
0.68
0.04
191
2
NH4+/NO3- molecular ratio:
3.7
Potassium sulphate - K2
N
P
K
Ca
Mg
S
Cu
Fe
Mn
Zn
B
Mo
Cl
Na
148.9
33.3
208.7
31.0
15.0
219.6
0.33
1.51
0.64
0.96
0.68
0.04
3
2
NH4+/NO3- molecular ratio:
3.7
Potassium nitrate - K3
N
P
K
Ca
Mg
S
Cu
Fe
Mn
Zn
B
Mo
Cl
Na
148.9
33.3
208.7
31.0
15.0
47.0
0.33
1.51
0.64
0.96
0.68
0.04
3
2
NH4+/NO3- molecular ratio:
0.2
TECHNOLOGY
51
AUG | SEPT 2014
ADVERTORIAL
in the sun. Dry weight was subsequently de-
or excess sulphate. It may also have resulted
termined on March 31, 2014.
from promoted cationic nutrient uptake. The
The trials each comprised 20 single tree repli-
NH4+ to NO3- ratio was least in the KNO3
cates of 3 treatments in a Randomized Complete Blocks design. The data were subjected
to Analysis of Variance. Mean separation
was based on the 5% LSD criterion.
nutrition: II. Factors affecting the ratios of sum of the cations:
sum of the anions in Italian rye-grass. The Journal of Agricultural Science 63: 103-108.
Ernest A.K. and Knight, A.H. 1977. Influence of the Level
of nitrate nutrition on ion uptake and assimilation, organic
acid accumulation, and cation-anion balance in whole tomato plants. Plant Physiol. 60:349-353,
solution. Ernst and Knight (1977) similarly
found increased dry matter production associated with increased NO3- nutrition in
Frost, W.B., Blevins, D.G., and Barnett, N.M. 1978. Cation pretreatment effects on nitrate uptake, xylem exudate, and
malate levels in wheat seedlings. Plant Physiol. 61:323-326
tomato. They suggested that increasing the
level of NO3- stimulates cation uptake and
Guohua, X., Magen, H., Tarchitzki, J., and Kafkafi, U.
2000. Advances in chloride nutrition in plants. Advances in
Agronomy 68:97-150.
translocation to the upper plant parts where
Results and Discussion
Figs. 1 and Table 3 show the differences in
shoot length on each measurement date in
both peach and apple. Table 3 also shows
number of leaves initiated, and fresh and dry
weight once the shoots were cut from the trees.
Growth was more vigorous in the trees treated
with the solution made up with KNO3 than in
the trees treated with the solution made up
with KCl or K2SO4. Vigour differences relat-
ing to the latter K sources were not apparent.
Leaf number per shoot, or shoot fresh or dry
weight bore a direct relationship with shoot
length. This indicates that the differences in
length encountered were not solely due to dif-
NO3 reduction mainly takes place.
-
Our results clearly indicate a probable
Jackson, W.A. and Williams, D.C. 1968. Nitrate-stimulated uptake and transport of strontium and other cations. Soil
Sci. Soc. Am. Proc. 32: 698-702
benefit of using KNO3 as opposed to KCl or
K2SO4 in supplying fruit trees with potas-
Kafkafi, U., Walerstein, I., and Friegenbaum, S. 1971.
Effect of potassium nitrate and ammonium nitrate on the
growth, cation uptake and water requirement of tomato
grown in sand culture. Israel J. Agr. Res. 21:13-20.
sium. Nitrification may render sufficiency
of conversion of NH4+ to NO3- after fertilization. However, this conversion is only ef-
Norton, J.M. and Stark, J.M. 2011. Regulation and measurement of nitrification in terrestrial systems. In Martin G.
Klotz, editor: Methods in Enzymology, Vol. 486, Burlington:
Academic Press, pp. 343-368.
ficient if soil temperature, pH and organic
matter content favour nitrification (Shammas, 1986). Additional research should be
carried out to ascertain the benefit of KNO3
Ragab, S.M. 1980. Effect of ammonium on anion uptake and
trans-root potential in sunflower roots. The Journal of Agricultural Science 94:479 - 482.
crops. Our results clearly show a benefit in
Shammas, N.K. 1986. Interactions of temperature, pH and
biomass on the nitrification process. Water Environment
Federation: Journal (Water Pollution Control Federation)
58:52-59.
as opposed to KCl or K2SO4 use in other fruit
both peach and apple in this study.
ferences in the extent of inter-node extension,
and also occurred as a result of differences in
Literature Cited
dry matter accumulation.
Blevins, D.G., Hiatt, A.J., and Lowe, R.H. 1974. The influence of nitrate and chloride uptake on expressed sap pH,
organic acid synthesis and potassium accumulation in higher
plants. Plant Physiol. 54: 82-87.
Enhanced shoot vigour in the trees treated
with the solution made up with KNO3 may
have resulted from the absence of chloride
Van Beusichem, M.L., Kirkby, E.A., and Baas, R. 1988.
Influence of nitrate and ammonium nutrition on the uptake,
assimilation, and distribution of nutrients in Ricinus communis. Plant Physiol. 86:914-921.
Zhu, S and Chen, S. 2002. The impact of temperature on
nitrification rate in fixed film biofilters. Aquacultural Engineering 26:221-237.
Cunningham, R.K. 1964. Cation-anion relationships in crop
Table 3 New shoot lengths on the dates of measuring, and number of leaves, fresh or dry weight after the shoots were cut from the trees.
New Shoot Length (cm)
Peach
18-Dec
25-Dec
03-Jan
08-Jan
15-Jan
22-Jan
29-Jan
Number of
Leaves
Fresh
Weight (g)
Dry Weight
(g)
KCl solution
15.9ab
22.2ab
30.1ab
31.5ab
33.1a
34.4a
34.7a
26.6a
14.4a
3.9a
K2SO4 solution
13.7a
19.4a
26.6a
27.7a
29.2a
29.9a
30.6a
24.2a
12.6a
3.5a
KNO3 solution
18.2
25
33.3
35.9
40.4
45.0
47.4
32.4
26.8
7.4b
0.0163
0.0372
0.0143
0.0017
0.0002
0.0001
0.0003
0.0000
0.0000
Treat. Sig. Level
b
0.0150
b
b
b
b
b
b
b
b
New Shoot Length (cm)
Apple
27-Dec
03-Jan
10-Jan
17-Jan
24-Jan
27-Jan
Number of
Leaves
Fresh
Weight (g)
Dry Weight
(g)
KCl solution
7.9a
17.7a
23.6a
29.3ab
33.7a
35.1a
27.2a
6.8a
2.0a
K2SO4 solution
7.9a
17.1a
23.1a
26.4a
31.3a
37.5a
25.3a
6.5a
1.9a
KNO3 solution
8.3
18.5
26.7
35.8
45.3
48.6
33.1
9.9
2.7b
0.9101
0.8147
0.4211
0.0549
0.0059
0.1333
0.0019
0.0055
0.0523
Treat. Sig. Level
a
a
a
b
TEGNOLOGIE
b
52
a
AUG | SEPT 2014
b
b