‘Ferti-K’, Soluble KCl for Fertigation:

The Israeli Experience and Approach

H. Magen (1)

(1) ICL Fertilizers

Paper presented at the 8th Fertilizer Latin America International Conference, Palm Beach, Florida, 13-15 April 1997

Abstract

Fertigation is the process of applying solid or liquid (fluid) fertilizers to crops via pressurized irrigation systems. Fertigation is the practice best suited for limited wetted area irrigation (micro-irrigation). Due to its semi-arid climate, Israeli agriculture is dependent on pressurized irrigation which allows full monitoring and saves water. Fertigation with N, P, and K is by far the most common, and in some cases the only, method of fertilizing orchards, vegetables, banana plantations, greenhouse crops, and drip-irrigated field crops such as cotton, maize and others. Approximately 65% of K2O applied to crops of all kinds is via fertigation systems. Comparative studies with potassium sulfate and potassium nitrate at our lab demonstrate that potassium chloride is the most soluble, and has the highest dissolution rate and nutrient concentration (in saturated solution). This makes it the most suitable K fertilizer for fertigation in terms of stock solution volume and ease of application. ICL Fertilizers’ Ferti-K (soluble KCl for fertigation) is also very convenient for “grass root” mixing at field level with Urea, Ammonium Sulfate, Ammonium Nitrate (as N source) and Phosphoric acid or Mono-Potassium Phosphate (as P source), to form NPK nutrient solution which uses raw materials available on the market. With this method, a maximum nutrient concentration may reach 11-13%. With ‘chloride sensitive’ crops, chloride management is achieved by monitoring the Cl- concentration in plants, soil and water. In arid and semi-arid areas, calculation of Cl- concentrations and load from KCl fertigation vs. irrigation water, shows the negligible contribution of KCl to the total Cl- input. Precipitation of 700 mm/year is already sufficient for leaching, thus no hazards from chloride accumulation are expected.

1

K Situation in Israel

Fertigation is the application of solid or liquid mineral fertilizers via pressurized irrigation systems, creating nutrient-containing irrigation water. Although the practice of commercial fertigation started only in the mid - 20th century, there is evidence that the concept of irrigation with nutrients dissolved in water was well known in the past. The first reported example dates back to ancient Athens (400 B.C.) where city sewage was used to irrigate tree groves (Young and Hargett, 1984). One of the major factors in promoting modern fertigation was the development of micro-irrigation systems (MIS) such as drip irrigation, jets and micro-sprinklers. Field experiments in Israel in the early 1960s showed that when localized sections of a field are irrigated, as in MIS, standard broadcasting of fertilizers is ineffective. The limited root zone and the reduced level of mineralization in the restricted wetted zone are the main reasons for the reduced nutrient availability to the plant (figure 1, 2). When this was recognized, fertigation was integrated in almost all MIS (figure 3).

Limited root zone with Micro Irrigation Systems (MIS)

Figure 1

Limited root zone - what does it mean?

l Nutrient reservoir is ~30% of total area, thus creating alimited supply of organic matter and mineralizationproducts.

l A more frequent replacement of nutrients is neededl Frequent irrigation intervals may cause leaching and loss

of nutrients.l Broadcasting fertilizers is inefficient.

Figure 2

2

Fertigation(soluble fertilizerssoluble fertilizers)

Filtering

Waterquantifying

Pressureregulating

Components of MIS

MIS

Figure 3

Israel is an unmatched example of the use of fertilizers by fertigation. In 1996, the Israeli farmer used an average of 115, 46 and 57.5 kg of N, P2O5 and K2O per hectare, respectively (figure 4). Over 50% of the N and P2O5 and 65% of the K2O is applied by fertigation. For K2O, clear liquid N-P-K, N-K or P-K solutions or soluble complex or binary fertilizers are the common formulations. Approximately 30% of K2O consumed is applied as solid soluble potassium chloride (KCl) either in by-pass tanks or as small volume stock solutions prepared by farmers. The other two portions, ~35% each, are 1) non-chloride K fertilizers in solid or liquid form, mainly as potassium nitrate and mono-potassium phosphate, and 2) as solid straight muriate of potash (MOP) broadcasted with mechanical spreaders (figure 4). K use by crops shows that most of the K applied is for horticulture crops (figure 5). The most common sources of potassium for fertigation in Israel are potassium chloride (KCl), potassium sulfate (K2SO4), potassium nitrate (KNO3) and mono-potassium phosphate (KH2PO4). The K fertilizer is chosen by price, solubility, anion type and ease of use.

57.5

46

115

Kg / ha as soluble KCl

as MOP mechanically spread

as non-chloridesource of K2O

Nutrient consumption per area unit & K2O use in Israel

0

50

100

150

200

250

K2O

P2O5

N

Figure 4

3

MAIZE11%

POTATO7%

APPLES3%

AVOCADO6%

BANANA4%CITRUS

14%

COTTON5%

VEGT.15%

FLORIC.7%

OTHERS19%

PEACH4% TOMATOES

5%

K use by crops in Israel(Source: Fert. & Chem., 1994)

Figure 5

Compatibility of K Fertilizers with Fertigation

The following characteristics are advantageous in ‘fertigation grade’ fertilizer: 1) complete solubility; 2) high nutrient content in the saturated solution; 3) fast dissolution in irrigation water; 4) no chemical interactions between the fertilizer and irrigation water, and 5) minimal interaction when mixed with other fertilizers (when a multi-nutrient stock solution is prepared). Solubility of K fertilizers. Solubility is defined as the amount of salt (grams) per volume (liter). Potassium chloride is the most soluble potassium fertilizer up to a temperature of about 20°C; at higher temperatures potassium nitrate is more soluble (figure 6). Both salts have an endothermic reaction when dissolved (the solution cools as the fertilizer dissolves) (figure 7). This phenomenon limits the solubility of KNO3 more than that of KCl, but diminishes after short time. KCl is marketed either as white or red/pink material. The source of the red color is the presence of 0.05% Fe-Oxide and other metal compounds in the material (PPIC, 1988). Since this fraction is insoluble (in water) and regular treatment with acids in fertigation systems cannot dissolve it, it is practically impossible to use red/pink KCl for fertigation. Clear evidence of its clogging ability exists.

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KNO3

KCl

KH2PO4

K2SO4

0 5 10 15 20 25 30 350

100

200

300

400

500

Temp (°C;F)

Solubility (gr. / liter)

Solubility of K fertilizers with temperature

32 41 50 59 68 77 86 95

Figure 6

0 10 20 30 40 502

4

6

8

10

12

Time (min)

Tem

pera

ture

(C)

KCl

K2SO4

KNO3

Change in temperature when dissolving K fertilizers (80% saturation, 10°C , 100 rpm) (Source: Elam et al, 1995)

Figure 7

Nutrient content of K fertilizers (at saturation). Nutrient content is defined as the value received by multiplying solubility by the percentage of the nutrient in the fertilizer. KCl yields the highest nutrient content at 10°C, achieving a concentration of 15% K2O, compared to only 8% with KNO3, and even less with K2SO4 and KH2PO4 (figure 8).

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Solubility and nutrient concentration of K fertilizers at saturation (10°C; 50°F)

Cl

S

P2O5

N

KCl KNO3 KH2PO4 K2SO40

150

300

450

600

0

2

4

6

8

10

12

14

16

Solu

bilit

y (g

r'/l)

% of plant food (K2O; anion)

SolubilityK2O (%)Anion (%)

Figure 8

Fast dissolution. This parameter is important when considering dissolution at field level for the calculation of irrigation and fertigation timing and intervals. Elam et al. (1995) showed the difference between KCl, KNO3 and K2SO4 dissolution rates (figure 9). Dissolution time (t90, the time needed to dissolve 90% of the salt added, in minutes) of KCl is much shorter and the K2O content is much higher, about 13% for KCl in 8 minutes, compared to 4% for K2SO4 in 25.2 min. and 9% for KNO3 in 15.6 min.

Dissolution rate of K fertilizers (80% saturation, 10°C, 100 rpm) (Source: Elam et al, 1995)

0 10 20 30 40 500

0.2

0.4

0.6

0.8

1

Time (min)

Frac

tion

Dis

solv

ed

KCl

K2SO4

KNO3

KCl K2SO4 KNO3

% K2O 12.0 3.9 6.5t 90 11.2 35.3 20.6% Salt 19.0 6.8 13.8

Figure 9 Chemical interactions between the fertilizer and irrigation water. The formation of precipitates in irrigation water due to the addition of fertilizer, is one of the most common problems farmers encounter at field level. The most common precipitates are Ca-P compounds at pH>7.0, when P fertilizers are added. Other common precipitates are Fe-P, CaSO4 and carbonate compounds. Since chloride salts are highly soluble, precipitation of its salts practically does not exist in such systems at levels of pH 4 - 9. A more accurate method of predicting precipitation under various conditions of pH and varying concentrations of ions is by the use of the computer program ‘GEOCHEM-PC’ (Parker et al., 1995). The program can predict the precipitation of

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any salts in irrigation water, and thus can be used successfully in fertigation management. Laboratory experiments with nutrient solutions showed a good correlation between the program’s predictions and the actual results (Magen, 1995a). Figure 10 shows the calculated precipitation results for three concentrations of P vs. given Ca concentration in water and changing pH. This demonstrate the difficulty of adding high concentrations of P at solution pH>6.

P concentration pH=6 pH=7 pH=8in nutrient solution

20 none none none

40 none OCP OCP, DCPD, HA

60 none OCP, DCPD

OCP - octacalcium phosphateDCPD - brushiteHA- Hydroxyapatite

Predicted formation of Ca-P precipitation by ‘GEOCHEM-PC’

[Ca] = 0.0035 mole/l

Figure 10

Field prepared stock solutions

In Israel, application of fertilizers through fertigation is executed by various methods (Sne, 1995; Magen, 1995b), including the technique of stock solution preparation. With this technique, farmers are using solid fertilizers such as ammonium sulfate, urea, potassium chloride and nitrate, phosphoric acid (liquid) and mono-potassium phosphate to prepare a “tailor made” stock solution. The stock solution is then injected (by pump) into the irrigation system, at rates of 2-10 liters per 1 M3 of water, depending on the desired concentrations of N, P and K. The outcome of this technique is ‘proportional application’, used mainly in light textured soils or very limited root zones. The other common practice is the use of a by-pass tank: solid fertilizer is added to a metal tank and part of the irrigation water is diverted to pass through and dissolve the fertilizer. This technique is called the ‘volumetric application’ and is very common with mature orchards and field crops. In order to meet the demand for ‘know-how’ of mixing solid soluble fertilizers, we conducted a series of experiments at our lab (Lupin et al. 1996). The aim of the work was to examine the preparation of mixed fertilizer solutions based on solid soluble fertilizers under “grass roots” field conditions, with minimal mixing. Urea, ammonium sulfate, phosphoric acid (liquid), mono-potassium phosphate and potassium chloride (‘Ferti-K’, fertigation grade) as N, P, and K sources, respectively, were examined for the preparation of clear liquid solutions (figure 11).

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Typical stock solutions prepared at field conditions...(1)

• K solution

• NK solutions

• PK solutions

• NPK solutions

materials used: Urea, Ammonium Sulfate; Phosphoric Acid,

Mono Potassium Phosphate; Ferti-K Potassium Chloride Figure 11

Various formulas with different sources of fertilizers at different ratios were examined. Clear NK, PK and NPK fertilizer solutions with at least 9-10% and up to 14% nutrients (N, P2O5, K2O) were prepared (figure 12). It was also found that when phosphoric acid is used in the formulation, this should be added to the water first to utilize the positive heat of the solution. Since the endothermic reaction of urea dissolution is marginal, the addition of KCl is after urea, thus the preparation of the solution is faster. When preparing a solution with ammonium sulfate, mono-potassium phosphate and KCl, the latter should be added first, followed by mono-potassium phosphate. The addition of ammonium sulfate as N source, reduced greatly the total nutrient concentration, due to precipitation of K2SO4. Change in the electrical conductivity (EC, 1:1000) of the various solutions was marginal, varying between 0.15 to 0.5 dS/m. Significant change in pH (1:1000) was only when phosphoric acid was added (pH=3.5-4.5). This pH range does not present any hazard to the irrigated root zone. In solutions containing mono-potassium phosphate and ammonium sulfate, pH (1:1000) was reduced to 5.0-6.0. A typical ‘what and how to do’ is presented with figure 13.

Ratio Formula Fertilizers EC (dS/m) pH (max.) (order) (1:1000) (1:1000)0-0-1 0-0-8 KCl +0.22 nd1-0-1 5-0-5 Urea/KCl +0.16 6-71-0-1 3-0-3 KCl/AS +0.37 6.50-1-3 0-3.2-9.6 Phos.A/KCl +0.36 3.40-1-3 0-3-9 MKP/KCl +0.22 5.61-2-4 2.5-5-10 Phos.A/Urea/KCl +0.50 4.0-4.51-2-4 2.5-5-10 MKP/Urea/KCl +0.27 5.61-1-3 1.5-1.5-4.5 MKP/KCl/AS +0.28 5.6

AS=Ammonium Sulfate; MKP=Mono Potassium Phosphate

Typical stock solutions prepared at field conditions...(2)(Source: Lupin et al, 1996)

Figure 12

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To prepare 100 l. stock solution type “3-6-12”:• fill 90 l in the tank,• add 16 kg Phos. Acid,• add 6.5 kg Urea,• add 20 kg Potassium Chloride,• bring volume to 100 l.

Apply 1 liter stock solution per 1 m3 water to reach30, 60 and 120 ppm of N, P2O5 and K2O, respectively.

Field level recommendation - what to do?...(3)

Figure 13

Chloride management

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 (Maas, 1986b). Unlike other micronutrients that form toxicity levels, chloride is non-toxic and its concentration in plant tissue can exceed that of other major nutrients. Another important characteristic is that chloride concentration in tissue can be easily reduced with proper irrigation management. Plants normally accumulate chloride at 50-500 mmoles/kg DW (0.18-1.8%). Higher rates, in saline conditions can cause damage. The ameliorating effect of chloride application was shown when chloride deficiency occurred. Chloride increased palm tree yields (Uexkull and Sanders, 1986), improved the quality of potatoes (Jackson and McBride, 1986) and suppressed corn stalk in maize (Heckman and Bruulsema, 1996). In recent years, research work regarding the effect of salinity on the quality of crops has taken place. In these studies, the fertigation system is used to add salts (mainly MgCl2, CaCl2 and NaCl) to the plants and by that to improve its quality. Mizrahi et al. (1988) found that with a saline irrigation regime the fruit quality of tomato improved. Siton et al. (1996) found that irrigation with saline water (up to EC=7dS/m, 53 meq/l Cl-) increased glucose and titratable acids concentrations, and improved the overall taste of the fruit. A decrease of approximately 25% in yield was observed for the high salinity treatments. It is necessary to emphasize the importance of MIS used in these studies, which allow an accurate and careful application of water and fertilizers. Citrus is a major crop in Israel. K fertilization is done mostly with KCl through fertigation, accompanied with foliar application of KNO3. The contribution of Cl- applied to the total salinity or to the total Cl- concentration is marginal (figure 14), especially with water containing >200 ppm Cl- (figure 15). Accumulation of Cl- in leaves is attributed not only to Cl- containing fertilizers, but also to a badly-planned irrigation regime. In such cases, applying 20-30% extra water, will leach the soluble salts and significantly reduce the Cl- concentration in leaves. The relative tolerance of different rootstocks and varieties for chloride is presented in figure 16.

9

Addition of Cl- in irrigation water with 0-0-8 K solution

(KCl only)

1. EC (1:1000) - +0.22 dS/m

2. pH (1:1000) - no change from background

3. +[Cl-] - for 80 ppm K2O = 58 ppm Cl- Figure 14

Cl concentration Cl applied in water (kg/ha) Cl applied in 500 Relative contributionin water (ppm) 500mm 1000mm kg/ha KCl (kg/ha) of Cl from KCl (%)

100 500 1,000 235 20-30%

200 1,000 2,000 235 10-20%

400 2,000 4,000 235 5-10%

Calculated comparison between Cl inputs from irrigation water vs. fertilization with KCl

Figure 15

Maximum permitted chloride concentration in irrigation water for variouscitrus varieties and rootstocks

**Rangpur lime, Cleopatra, Grapefruit **Rough lemon, Tangelo, Sour orange

* Grapefruit >400

**Sweet orange, Citrange, Trifoliate, Troyer citrange

* Shamouty X sweet orange

***Rough lemon, Marsh grapefruit

0 200 400 600 800

Chloride concentration (ppm)

*Hauzenberg, 1965

**Maas, 1986a; Bernstein, 1974

***Levy and Shalhevet (unpublished), 1989

58ppm

Figure 16

In a long term survey executed in Israel (Hauzenberg, 1965), it was found that winter rain of approximately 700 mm is sufficient to leach the ‘summer load’ of chloride built up by irrigation and fertilization. It was then suggested that irrigation should be carried out also with relevance to winter rain, in order to avoid the build up of salinity. These recommendations are the basis of the Israeli irrigation recommendation.

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Proper water management and the technique of fertigation present a unique opportunity to control the level of salts in plant rootzones. This is even more valid when saline water is used, in which the management of irrigation, and to a lesser degree, fertilizers, actually dictates the salinity level prevailing at the root zone. With fertigation, the depth and distribution of fertilizers at the root zone is fully controlled, thus serving as another tool for controlling the salts level. With routine analysis of plant, soil extract and water, full control is then achieved.

References

Bernstein, L. 1974. Crop growth and salinity. In: Shilfgaarde J van (ed). Drainage for Agr. Agronomy 17:39-54. Elam, M., Ben Ari, S. and H. Magen. 1995. The dissolution of different types of potassium fertilizers suitable for fertigation. A paper presented in Dhalia Greidinger International Symposium on Fertigation, Haifa, Israel Jackson, T. L. and R. E. McBride, 1986. Yield and quality of potatoes improved with potassium and chloride fertilization. In: T. L. Jackson (ed). Chloride and Crop Production. Papers of a symposium, Am. Soc. of Agron. PPI. Special Bulletin No. 2. Hauzenberg, Y. 1965. Salinity survey in Israel. Ministry of Agriculture, Extension Service (in Hebrew). Heckman, J. R. and T. W. Bruulsema. 1996. Chloride suppresses corn stalk rot: update. Better Crops 80:4. Lupin, M., Magen, H., and Z. Gambash. 1996. Preparation of solid fertilizer based solution fertilizers under “grass roots” field conditions. Fertilizer News, V 41:12, pp 69-72. Maas, E. V. 1986a. Salt tolerance of plants. Applied Agric. Res. 1:12-26. Springer Verlag. Maas, E. V. 1986b. Physiological response of plants to chloride. In: T. L. Jackson (ed). Chloride and Crop Production. Papers of a symposium, Am. Soc. of Agron. PPI. Special Bulletin No. 2. Mizrahi, Y., Taleisnik, E., Kagan-Zur, V., Zohar, Y., Offenbach, R., Matan, E., and R. Golan. 1988. A saline irrigation regime for improving tomato fruit quality without reducing yield. J. Am. Soc. Hort. Sci. 113:2. pp202-205. Magen, H. 1995a. Influence of organic matter on availability of Fe, Mn, Zn and Cu to plants. Msc. thesis, Hebrew University of Jerusalem. Magen, H. 1995b. Potassium chloride in fertigation. In: E. Rosenberg and S. Sarig (eds.). 7th Int. Con. on Water and Irrigation, Tel Aviv, Israel, 13-16 May. Parker, D.R., Norvell, W.A., and R.L. Chaney. 1995. GEOCHEM-PC - A chemical speciation program for IBM and compatible personal computers. In: Loeppert, R,H., Schwab, A.P. and S. Goldberg (eds.). Chemical equilibrium and reaction models. Soil Sci. Soc. Am. (SSSA), Madison, Wisconsin, USA.

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Siton, D., Kravzhick, S., Plaut, Z., and A. Gravve. 1996. High quality tomato production with saline water. A report for 1993-1994. BGUN-ARI-9-96. The Inst. for App. Res. Ben-Gurion Univ. (in Hebrew). Sneh, M. 1995. The history of fertigation in Israel. In: Proc. Dhalia Greidinger Int. Symp. on Fertigation. Technion, Haifa, Israel, 26 March - 1 April. pp 1-10 Uexkull, H. R. and J. L. Sanders. Chlorine in the nutrition of palm trees. In: T. L. Jackson (ed). Chloride and Crop Production. Papers of a symposium, Am. Soc. of Agron. PPI. Special Bulletin No. 2. Young, R.D., and N.L. Hargett. 1984. History, growth and status. In: J. M. Pots (ed). Fluid Fertilizer. Tennessee Valley Authority, Bull. Y-185.

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Additional slides presented

Fertigation

Fertilization + Irrigation

KCl

Why to go for KCl?

• Its cheap & its there,• Its easy to apply,• Its a good partner to your local N & P,• Its very compatible with water and other fertilizers.

13

Methods of Fertigation

Injectionby pumps(liq)

Suction by venturi(liq)

Applicationby pressuredifferential(solid & liq)

slides

Types of ‘Fertigation grade’ fertilizers

• Solid soluble NPKs,

• Liquid fertilizers,

• Solid soluble single fertilizers

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Make your own tailor-made stock solution:

• save ‘water’ transportation,• gain full flexibility to meet plants’ needs

• use local N (and P)

Ferti-K : Potassium Chloride for Fertigation

• fully soluble (< 0.075% insoluble)

• no clogging of filters or emitters

• applied as solid or liquid

• fast dissolution

• compatible with other N & P fertilizers

slides

15

Typical crops for FERTI-K application

• Cotton• Sugarcane• Maize• Banana, Plantain• Oil Palm• Citrus• Tomato, Lettuce other veg.• Pineapple• Deciduous

To apply thru

micro-irrigationsystems

Are you afraid of the Chloride?

>700mm1.

2. Leaching with MIS

16

17

Typical K fertilization recommendation in Citrus(Israel 1996)

• according to leaf analysis, 100-300 kg K2O/ha (160-500 KCl) are applied

• 30% as bulk broadcasted at middle of rainy season (February)

• 70% applied thru fertigation between April to August, at 6-12 doses

slides

Conclusions

ž The rapid development of MIS presents more challenges to Fertigation

ž N & K fertigation are vital components in MIS

ž Fertigation grade KCl is the most efficient solution for K application in terms of price, solubility, dissolution time and K content

ž Ferti-K presents an ideal and proven solution for vast K application as straight, industrial prepared and in tailor made nutrient(s) solutions

ž Chloride can be easily monitored and managed with MIS