Potassium in fertigation systems
Hillel Magen ([email protected]), Coordination China,
International Potash Institute (IPI), Basel, Switzerland
Introduction
Potassium (K) is an essential plant nutrient that plays a very important role in plant growth and
development. Its functions are mainly in pH stabilization, osmoregulation, enzyme activation and
membrane transport processes. Its uptake is highly selective, and transport is extremely mobile.
Horticultural crops take potassium in large quantities, especially at fruit filling stages. Fertigation
systems allow adjusting K rates according to crop’s demand. Nutrient supply to non bearing, young
fruit trees is characterized by constant applications of nutrients, including K, in order to maximize
growth speed; whilst at fruit bearing age, K application is usually practiced from the onset of new flash
leaves till fruit bearing.
Potassium is applied through fertigation by using various sources of K salts such as potassium
chloride (KCl), potassium sulphate (K2SO4), potassium nitrate (KNO3) and mono-potassium
phosphate (KH2PO4). Among the less common K fertilizers are potassium thio-sulphate (K2S2O3) and
potassium carbonate (K2CO3). The K fertilizer required for specific application is chosen according to
its agronomic value, availability and ease of use, and price.
Dissolving K fertilizers is relatively easy due to the nature of K salts. Rapid full dissolution is achieved
with relatively high nutrient content. The solution obtained can be used either as a stock solution, or
for direct application, depending on the concentration of nutrients required in the irrigation water.
Example of a fertigation program is described, showing the various considerations Vis a Vis quantity,
timing and system considerations.
5th Fertigation Training Course, Baoding, AUH, June 2004
International Potash Institute, P.O.Box 1609, Basel, Switzerland
Page 1/13
Agronomic aspects of K fertigation
K in fertigation or in pre-plant of muskmelon?
Is split K fertigation superior to a one time pre-plant application? An experiment by Hochmuth and Gal
(2001) compared K fertigation to pre-plant K application, and types of K fertilizers, in Athena'
muskmelon (Cucumis melo var. reticulatus [C. melo var. cantalupensis] upensis]), grown during 1999
in Florida, USA. Plants were raised on polyethylene-mulched raised beds. K was applied for the
season from KCl, K2SO4, or KNO3. The K was applied either 100% pre-plant incorporated in the bed
or in 12 equal weekly injections through the drip irrigation system. N was supplied at 225 kg N ha-1
from NH4NO3 and KNO3. The results of this experiment showed that early and total yield were not
affected by K source, but fertigated K resulted in a greater total-season fruit production.
K fertigation and K concentration in leaves of apple trees
Can we deal with only N & P fertigation and omit K? Apple is a major fruit crop in many regions of the
sub-tropical and temperate climate zones. In many of these regions there is a need to irrigate and
fertigate the crop during the dry season. The effect of omitting K from the fertigation program was
tested in high-density planted Summerland McIntosh apple trees (British Colombia, Canada; Neilsen
et al., 1998). The trees were fertigated with 40 g N and 17.5 g P/tree annually. By the third growing
season, leaf K decreased to 0.82% dry mass, and soil K of 50-60 g kg soil indicated K deficiency. The
correction of K deficiency was done by the applications of 15-30 g K/tree (30-60 kg K2O/ha) applied
as granular KCl directly beneath the emitters in spring, or as KCl applied in fertigation. K application
increased fruit red color, size and titratable acidity when leaf K was <1%. Fruit Ca and incidence of
bitter pit or core flush were unaffected by K applications. The application of granular KCl under the
emitter demonstrates the effective dissolution and mobility in soil of the KCl applied.
Fertigated cherry trees response to fertigated KCl
Cherry is defined as ‘sensitive’ crop to salinity. Callan and Westcott (1996) investigated fertigation
with KCl, KNO3 and K2SO4 in Sour cherry (cv. Montmorency trees grafted on Mahaleb [Prunus
mahaleb] rootstocks), at 0, 0.35, 0.7 or 1.4 kg K2O/tree (0, 140, 280 and 560 kg K2O/ha) at intervals of
4 biweekly applications each year beginning 2 weeks after flowering. It was found that maximum fruit
yield was obtained at a foliar K concentration of 1.5-2.0%. Non-Cl sources of K maintained foliar K
within the sufficiency range and increased fruit yield in one year, had no effect on fruit size or quality
and suppressed uptake of Ca and Mg in relation to the amount of added K. During the third year high
levels of fertigated KCl resulted in Cl toxicity, suppression of P uptake and increased Mn uptake. This
demonstrates that a proper management is required when very high doses of K are applied to salinity
sensitive crops.
Tomatoes: Moderate salinity is beneficial
Chloride is found in almost all soils, plants and irrigation water. It is readily available in soil; therefore
its accumulation in plants is relatively fast. Another important characteristic is that chloride uptake by
plants can be easily reduced with proper irrigation management. Plants normally accumulate chloride
Page 2 /13
at 50-500 mmol/kg DW (0.18-1.8%). Higher concentrations than 1.8% (DW) under saline conditions
can cause damage.
In a fertigation experiment in soil-less tomatoes with different K sources, increase in the salinity was
due to increased level of Cl (Chapagain et al., 2003; table 1). The increase from 1.83 to 2.01 dS/m
(table 1) is reflecting the full conversion of K source from KNO3 to KCl. The level of 2.01 dS/m is still
well below the yield limit by high salinity level in tomato (3.5 dS/m; Nukaya et al., 1991).
Table 1: Concentration of nutrients in the fertigation solution of different treatments. The values are
mean ± SE (Chapagain et al., 2003).
K
KCl/KNO3
K2O Ratio
P
Ca
Mg
Na
NH4
NO3
Cl
pH
------------------------------------------------------------ (mg/L) -------------------------------------------------------
EC
.
(dS/ m)
0 / 100
176±6.5 49.1±1.6 71.1±3.0 40.1±0.89 135.9±3.21 13.7±5.15 286±13.3
239±6.75
7.15 ± 0.08 1.83 ± 0.04
40 / 60
183±7.7 51.0±1.6 86.0±3.0 41.4±0.87 138.8±3.21 13.5±4.09 267±12.8
298±6.10
6.97 ± 0.05 1.92 ± 0.03
60 / 40
182±7.5 51.7±1.8 89.2±3.5 41.2±0.87 13.6.9±3.66 21.1±4.38 255±13.3
327±6.96
6.86 ± 0.05 1.94 ± 0.04
100 / 0
182±7.5 50.2±2.4 95.5±3.3 41.2±0.85 135.4±3.49 30.8±4.16 218±19.3 385±10.18 6.58 ± 0.07 2.01 ± 0.04
Replacement of KNO3 with KCl in greenhouse tomatoes was tested in Israel during 2000 and 2001
(Chapagain et al, 2003). This conversion means 1) higher EC with higher Cl rates, 2) higher Cl levels
in the nutrient solution and 3) slight difference in the NH4 / NO3 ratio (table 1). The results of this twoseason experiment, showed no difference in yield (table 2) but higher post harvest quality parameters
(table 3) when K was supplied as KCl/KNO3 of 60/40%. As EC of the nutrient solution did not exceed
4.5 dS/m, no reduction in yield was expected. Quality of water is also a significant factor in decisionmaking. Similar findings are well known for the last 20 years. At a field experiment in tomatoes for
industry, a short-term induced salinity (6-16 dS/m, ECSP), during the late growth stages, increased
TSS, DM, acidity and fruit colour (Orly and Rudich, 1984. in Hebrew).
Table 2: Effects of K source in the nutrient solution on fruit size and yield of tomato plants (Chapagain
et al, 2003).
KCl/KNO3
K2O Ratio
Fruit yield
Number of fruits per
plant
Fruit weight
Fruit diameter
(g)
(mm)
0 / 100
4897
(g/pl)
40.5
121
66.3
40 / 60
4862
40.5
120
68.0
60 / 40
4851
40.2
120
66.4
100 / 0
4695
39.8
119
66.2
Values are mean of fruits from truss 1 to 8 of 32 plants of 4 replications. Results were not significantly
different between treatments.
Page 3 /13
Table 3: Effects of K source in the fertigation solution on post harvest quality of tomato fruits
(Chapagain et al, 2003).
Treatment
Firm fruit
Rotten fruit
Fruit with calyx
Calyx freshness
Blotchiness
y
(%)
(%)
(%)
(1-3)
(%)
100% KNO3
51.5 b
2.67 a
97.67 a
2b
5.0 a
40% KCl
60.33 a
2.33 a
97.67 a
2.03 b
4.67 a
60% KCl
68.33 a
1.67 ab
97.88 a
2.1 b
5.83 a
100% KCl
59.33 a
0.33 b
98.17 a
2.18a
3.33 a
Values are means of 96 samples (8 fruits per sample) from truss 1 to 8 of 32 plants of 4 replications.
Means in each column followed by different letters are significantly different at p<0.05 by TukeyKramer HSD test.
Y
Calyx freshness: 1=low, 2=medium, 3=high.
Chloride vs. nitrate
A trigger for conversion of KNO3 with KCl is the possibility to reduce levels of accumulated NO3 in the
plant by increasing Cl levels at the root zone. Chapagain et al (2003) showed significant decrease in
accumulated NO3 levels in tomato plants (table 4).
Table 4: Effect of KCl as source of K on cumulative uptake of K, Cl and NO3 and NO3 in fruit by
tomato plants from beginning of the treatments solution to 105 days.
–1
KCl/KNO3
Cumulative nutrient uptake (mg plant )
Fruit composition
K2O Ratio
K
Cl
NO3
NO3 (mg g
0 / 100
19477 a
5379 b
31891 a
40 / 60
21802 a
7805 ab
30760 a
0.011 ab
60 / 40
19927 a
11615 a
27389 ab
0.009 ab
100 / 0
20291 a
12705 a
22823 b
0.008 b
–1
FW)
0.015 a
Chloride vs. sulphate
Uptake of chloride is of concern in various intensive growing systems. Nukaya et al. (1991) found that
tomato yield was not affected by the concentration of Cl up to 13 mmol/l (450 ppm), when EC in the
root environment was kept at 3.5 dS/m. High levels of SO4 in the solution (3.8 mmol/l) caused
significant increase of blossom end-rot phenomena in fruit (table 5).
Page 4 /13
Table 5. Effects of different N-S-Cl ratios on yield and quality of tomatoes grown in recirculating
solution (adopted from Nukaya et al., 1991). .
Treatment
Yield
Soluble solids
Shelf life
BER (till end of growth
N-S-Cl (ppm)
(Fruit/m )
(% Brix)
(Days)
(% Of total fruit no.)
224 – 160 - 105
305
4.8
14.4
9.1
154 – 240 - 105
308
4.7
13.0
9.5
stage)
2
84 – 320 - 105
328
4.8
13.5
8.0
154 – 160 - 280
324
4.9
13.9
7.8
84 – 160 - 455
314
4.9
12.1
6.0
154 – 240 - 280
338
4.9
12.4
6.1
Economics
The general recommendation in the Netherlands for K supply in greenhouse tomatoes is for monopotassium phosphate and potassium sulphate for P and S requirements, the remaining K quantity by
KNO3 and KCl (Voogt, 2001). Hand and Fussel (1995) compared the use of KCl to KNO3 in tomatoes
grown on rock wool, in order also to calculate the environmental and financial benefits to the UK
tomatoes grower. They found that savings as high as £4000/ha can be achieved with the use of KCl,
rather than potassium nitrate. This benefit brings in account savings due to cost of fertilizer as well as
penalties for nitrate discharge. Csizinsky (1999) compared three potassium sources for tomato grown
in a full-bed polyethylene mulch-seepage (furrow). Comparing KCl to KNO3 and K2SO4, it was found
that K source had little effect on fruit size or yield. In this case, the per hectare cost of 270 kg K2O/ha
would be $118 for KCl, $228 for KNO3 and $212 for K2SO4.
K fertigation in strawberries: Taking advantage of the high quality irrigation water.
Potassium nitrate and Calcium nitrate are the main sources of K and Ca in fertigated strawberries
grown in North Western Argentina. A considerable loss of marketable yield is usually attributed to
excessive N rates applied especially in spring. Different K sources can be changed to maintain the
levels of fertilization with K and Ca, without increasing N levels (Kirschbaum et al., 2001). Water
quality used for irrigation in this region is very high (very low EC). IPI and INTA – EEA Famaillá
initiated a joint project to explore the possibility of reducing N levels (from 205 to 148 kg N/ha)
substituting KNO3 with KCl and K2SO4 (at 20:80% ratio). Bare-root 'Camarosa', 'Milsei' and 'Sweet
Charlie' strawberries were grown using polyethylene-mulched and fumigated beds. The target levels
of P2O5 and K2O were constant, at 100 and 285 kg/ha, respectively. Five treatments were weekly
applied from August to October (table 6). The results show that N level should be reduced as it has
no effect on the marketable fruit (g / plant) and fruit weight, and there is no clear preference to K
source. This implies that there is an advantage to use K source without N at the fruit bearing / harvest
stages of the crop.
Page 5 /13
Table 6: Effects of K source in the fertigation solution on yield of ‘Camarosa’ strawberry fruits during
2000 & 2001 (Kirschbaum et al., 2001).
Treatment
K source
(N-P2O5-K2O kg/ha)
Marketable
Marketable
Average fruit
Average fruit
fruit (g./plant)
fruit (g./plant)
weight (gr)
weight (gr)
2000
2001
2000
2001
205-100-285
KCl
669 b
724 a
16.5 b
16.8 a
148-100-285
KCl
747 ab
712 a
20.5 a
16.9 a
205-100-285
KNO3
766 ab
698 a
17.9 b
16.9 a
148-100-285
KCl+ KNO3
814 a
708 a
18.0 b
16.7 a
148-100-285
K2SO4+ KNO3
738 ab
732 a
19.7 ab
16.6 a
Means in each column followed by different letters are significantly different at p<0.05.
Treatments had no effect on the content of soluble solids (Brix) and fruit firmness (table 7).
Table 7: Effects of K source in the fertigation solution on brix and firmness (kg/cm) of ‘Camarosa’
strawberry fruits (2001, Kirschbaum et al., 2001).
Treatment
K source
Brix
(N-P2O5-K2O kg/ha)
Firmness
(kg/cm)
205-100-285
KCl
7.58
4.07
148-100-285
KCl
7.44
4.12
205-100-285
KNO3
7.43
4.35
148-100-285
KCl+ KNO3
7.28
4.15
148-100-285
K2SO4+ KNO3
7.23
4.28
Means in each column followed by different letters are significantly different at p<0.05.
K fertigation in avocado trees: Calculating soil’s moisture.
Avocado trees are very sensitive to chloride accumulation; under sub-optimal irrigation management
its leaves develop scorches even when irrigation water contains 80 ppm Cl (personal
communication). Under such conditions, addition of KCl to fertigated trees may cause damage. In
Israel, avocado is grown in areas with winter precipitation of 250-800 mm. Irrigation and fertigation
take place mostly in summer. In order to reduce salinity damage, yet to save costs, farmers adopt the
following strategy:
•
Fertigation of KCl during end of winter, in order to dilute concentrations with the high water %
in soil,
•
Water management policy to ensure leaching of salts,
•
Fertigation with KNO3 during mid and late summer.
These techniques saves costs and optimise the use of different K sources according to plant’s needs,
soil moisture, and available budget.
Page 6 /13
P & K fertigation in eggplants
Eggplants are defined as “moderately salt tolerant” plant (Shimose et al., 1991). High levels of N, P
and K levels were used to assess yield and quality of autumn and spring eggplants grown in tuff filled
containers under plastic cover protection (Zipelevish et al., 2000). This experiment demonstrate the
form in which high levels of nutrients is applied. N source was solely from KNO3, at constant level of
150 ppm, phosphate sources used were phosphoric acid (0-0-62) and mono-potassium phosphate (052-34), and K sources were potassium nitrate (18-46-0), mono-potassium phosphate (0-52-34), and
KCl (0-0-61). Treatments are described in table 8 and yield of class A & B is presented at table 9.
Table 8: List of treatments, with the various EC, P & K concentrations ((Zipelevish et al., 2000).
EC
Phosphate fertilizer
(dS/m)
Type
Potassium fertilizer
(P2O5, ppm)
Type
(K2O, ppm)
2.24
Phos. Acid
41
KNO3
540
2.24
Phos. Acid + MKP
82
KNO3 + MKP
564
2.24
Phos. Acid + MKP
123
KNO3 + MKP
3.90
Phos. Acid
41
KNO3 + KCl
1080
588
3.90
Phos. Acid + MKP
82
KNO3 + KCl + MKP
1104
3.90
Phos. Acid + MKP
123
KNO3 + KCl + MKP
1128
Table 9: Cumulative number and yield of eggplant fruits (Zipelevish et al., 2000).
EC
(dS/m)
Solution composition
(P2O5, ppm)
2.24
41
(K2O, ppm)
540
Class A fruit
No.
15.2
Class B fruit
-2
Weight (kg/m )
No.
Total
-2
Weight (kg/m )
Weight (kg m
3.7 ab
11.6 b
1.8 a
5.5
-2
b**
2.24
82
564
16.2 ab
3.9 ab
10.2 b
1.5 a
5.4
2.24
123
588
18.2 a
4.2 a
10.7 b
1.8 a
6.0
3.90
41
1080
11.7 c
2.7 c
14.3 ab
2.0 a
4.7
3.90
82
1104
10.1 c
2.6 c
17.0 a
2.0 a
4.6
3.90
123
1128
14.5 b
3.3 bc
14.2 ab
2.2 a
5.5
The results show that high phosphate levels up to 128 (P2O5, ppm), at both levels of EC tested, are
needed to keep optimal eggplant yield and quality. High K levels reduced fruit size and class A yield.
Page 7 /13
K fertilizers used in fertigation and their characteristics
As fertigation requires dissolution of fertilizers in water, various technical and chemical aspects of this
procedure are of interest. In this part, a comparison between various fertilizers and their
characteristics in solutions is discussed.
Table 10: Nutrient content, pH and value of onion concentrations of various K fertilizers.
Fertilizers
N-P2O5-K2O
K2O content
Formula
(%)
Formula
Anion
pH
concentration
(1 g/L at
(%)
20oC)
Potassium chloride (1)
0 – 0 – 61
61
KCl
7.0
46 (Cl)
Potassium nitrate
13 – 0 – 46
46
KNO3
7.0
13 (NO3)
Potassium sulphate (1)
0 – 0 – 52
52
K2SO4
3.7
18 (S)
Mono-potassium
0 – 52 – 34
34
KH2PO4
5.5
52 (P2O5)
0 – 0 – 25
25
K2S2O3
7.0-8.2
17 (S)
phosphate
Potassium thio-sulphate
(1) Fertigation grade.
When supplying plant’s demand, K2O content (%) in the fertilizer is brought in account for calculating
the type of fertilizer required (table 10).
While potassium chloride and potassium nitrate have neutral reaction (pH=7), application of
potassium sulphate reduces pH of soil solution. Mono-potassium phosphate buffers solution’s pH and
will not reduce pH below 5.0 regardless of its concentration. This is valuable in hard water with high
pH, when it is required to safely reduce pH.
Chloride is a microelement required for plant nutrition. Chloride is found in soil and irrigation water,
but in some cases its deficient. Applying potassium nitrate supplies plant with both K and N in the
nitrate form. This is an advantage when nitrate and no chloride are required, but at periods when
there is need for high dose of K but excess of nitrate may damage fruits quality, another source of K
is preferred. Potassium sulphate is a good source for S in fertigation. Mono-potassium phosphate
contains high level of P2O5, which makes it an ideal source for the whole P required, along with about
20-30% of the K. Another source for S in the solution is the highly soluble potassium thio-sulphate.
Table 11: Amount of fertilizer required for supplying 300 kg K2O ha-1 (a typical quantity for 1 hectare
citrus trees).
Fertilizers
N-P2O5-K2O
K2O content
Quantity of fertilizer required
for 300 kg K2O/ha
Formula
(%)
Potassium chloride
0 – 0 – 61
61
Potassium nitrate
13 – 0 – 46
46
652
Potassium sulphate
0 – 0 – 52
52
577
Mono-potassium
0 – 52 – 34
34
882
0 – 0 – 25
25
1200
492
phosphate
Potassium thio-sulphate
Page 8 /13
Solubility and dissolution rate
An essential pre-requisite demand for the use of solid fertilizers in fertigation is their complete
dissolution in the irrigation water. Solubility of K salts is strongly affected by temperature (Table 12).
Potassium chloride is the most soluble K fertilizer up to ~25°C. The solubility of KNO3 increases
sharply with temperature, but at ambient and lower temperatures, its solubility decreases very quickly
and becomes significantly lower than that of KCl. K2SO4 is the least soluble over the entire
temperature range.
Dissolution rate was compared at controlled conditions (Elam et al., 1995). KCl presented the highest
dissolution rate (t90 = 5 minutes at 10ºC). KCl dissolution (expressed as t90) was twice faster
compared to KNO3 and almost 8 times faster compared to SOP (table 12).
Table 12: Solubility and dissolution rate (expressed as
t90)
of potassium fertilizers at different
temperatures.
b)
KCl
K2SO4
KNO3
Temperature
(°C)
Solubility
(g/100 g water)
t90
(minutes)
Solubility
(g/100 g
water)
t90
(minutes)
Solubility
(g/100 g
water)
t90
(minutes)
10
31
5.0
9
38.7
21
12.5
20
34
3.9
11
23.2
31
7.3
30
37
-
13
-
46
-
a)
a)
t90 is defined as the time in minutes needed to dissolve 90% of the fertilizer, at 10 & 20°C.
b)
Standard grade K2SO4 (not fertigation grade) was used in this experiment
Source: Elam et al., 1995.
Calculation of solubility with the K content of each fertilizer shows that KCl gives the highest percent
of K in the solution at each temperature (Table 13). This influences the volume of the storage tank
required: at 10° C, the tank volume needed to prepare a saturated solution of KNO3, K2SO4 or
KH2PO4 must be twice or three and three times larger, respectively, than that required when KCl is
used, for the same amount of K2O.
Page 9 /13
Table 13. Amount of K2O in saturated solutions of potassium fertilizers
Temperature
KCl
K2SO4
KNO3
KH2PO4 (1)
-3
Kg K2O m of saturated solution
(°C)
0
138
37
54
43
10
149
46
81
52
16
156
56
99
59
30
170
61
145
74
(1) KH2PO4 contains also high concentration of P2O5: at each temperature level, P2O5 level is
1.53 of K2O.
Heat released / absorbed at dissolution
The heat of solution is the amount of heat per unit weight; either needed or produced when a material
is dissolved in water. Most dry K fertilizers absorb heat from the water upon dissolution, thus lowering
the temperature of the solution (endothermic reaction). For example, under field conditions, it takes 4
minutes to fully dissolve and to prepare a 14% KCl solution, and the temperature drops from 10oC to
4oC (Lupin et al., 1996).
Heat of solution data of the chemical compounds is useful when preparing nutrient solutions with
different fertilizers. For example, the dilution of phosphoric acid is an exothermic reaction, resulting in
a rise of the temperature of the solution. This can be used to minimize the endothermic reaction of
urea or KCl (Lupin et al., 1996, table 14).
Table 14: NPK formulations of tailor-made field solutions, amount and order of added fertilizers and
solution characteristics (Lupin et al., 1996).
Formula
Quantity added (kg / 100 litre tank)
N-P2O5-K2O
(% wt/wt)
3.3-3.3-3.3
urea
7.2 (2)
4.4-4.6-4.9
9.6 (2)
4.7-1.6-4.7
10.2 (2)
6.4-2.1-6.4
13.9 (2)
Phosphoric
Mono-potassium
Potassium
acid
phosphate
chloride
5.3 (1)
5.4 (3)
8.8 (1)
2.6 (1)
4.0 (1)
Specific
PH
EC
gravity
(1:1000)
(1:1000)
(wt/vol)
1.08
dS/m
3.3
0.30
3.0 (3)
1.11
5.7
0.12
7.7 (3)
1.08
3.7
0.22
8.2 (3)
1.17
5.7
0.20
(1 to 3): order of adding the fertilizers to the solutions.
Chemical interactions between the fertilizer and irrigation water
The formation of precipitates in irrigation water due to the addition of fertilizers is one of the most
common problems farmers encounter at field level. Insoluble particles tend to clog emitters of drip
lines. Common precipitates are Ca-P and Ca-SO4 compounds occurring at pH>7.0, when P or
Page 10 /13
sulphate containing fertilizers are added to ‘hard’ water (high concentration of Ca and carbonate /
bicarbonate rich irrigation water). At such conditions, salting out of K2SO4 after adding KNO3 and
ammonium sulphate, salting out of CaSO4 after adding K2SO4 to irrigation water with high Ca level may occur. Since chloride salts are highly soluble, precipitation of its salts practically does not exist in
such systems.
Potassium in liquid fertilizers
Clear liquid fertilizers used for fertigation contain dissolved urea, ammonium nitrate and ammonium
sulphate, either individually or in combination as the N source, orthophosphate as the P2O5 source
and KCl, K2SO4, KNO3 and KH2PO4 either individually or in combination as the K2O sources. Table 15
presents some examples from the Israeli fertilizer industry.
Table 15: Selection of various formulas of liquid fertilizers used in Israel (source: Sne, data from
Ministry of Agriculture. Israel, 1989).
Fertilizers source
Main uses
N-P2O5-K2O
Salting out
pH
(% wt/wt)
Temperature (C°)
(1:1000)
KCl
Field crops, orchards
0-0-15
NH4NO3+H3PO4+KCl
Orchards
19-5-0
6
0.0
7-7-7
15
3.1
Urea+NH4NO3+ H3PO4+KCl
NH4NO3+MKP+KNO3
Field crops
Green-houses
4-0-12
5
4.5
0-10-10
5
0.3
8-8-8
13
0.6
8-0-12
12
7.6
7-0-7
14
3.5
6-6-6
3
3.5
3-0-9
12
3.5
(usually chelated micro
nutrients added)
Optimisation is being offered to the farmer in term of nutrient source, ratio between nutrients and
price.
References
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