Properties of solid and liquid fertilizers
Each fertilizer has characteristic properties that make it different from all others.
Fertilizers are classified into two main groups:Solid fertilizers and liquid fertilizers.
Each group is characterised according to the following properties:
The concentration of nutrient elements (N; P2O5; K2O).
The chemical compounds which make up the fertilizer.
The volume weight of the fertilizer.
The color of the fertilizer.
The turbidity of the liquid fertilizer solution
The physical condition of the solid fertilizer: cristallic, powdery, prilled or granulated
The pH of the fertilizer solution.
The corrosivity of the liquid solution.
The required storage conditions and the maximum period of storage.
Its fitness for the various fertilizer application technologies.
Settling out (crystallization) temperature of the liquid fertilizer.
The soil, substrate and crops for which the fertilizer is recommended
The concentration of nutrient elements
A fertilizer solution may contain one or more of the main- or macro- nutrients.
Nitrogen (N); Phosphorus (P) ; Potassium (also called Kalium) (K).
Some times it may be necessary to supply also secondary elements: Calcium (Ca); Magnesium (Mg); and Sulphur (S).
Special fertilizer solutions contain also micro- nutrients, elements that plants require only in very small amounts: Iron (Fe); Zinc (Zn); Manganese (Mn); Molybdenum (Mo); Boron (B); Copper (Cu).
Important !! The concentration of the macro-nutrients in a fertilizer is given in percentage per weight units, e.g.: grams of the macro-nutrients (N, P2O5, K2O) per 100 gram of fertilizer (gr/100 gr). The concentration of micro- elements is generally expressed in parts per million (ppm), e.g. milligrams of pure element in 1 Kg of fertilizer (mgr/Kg) or in grams of pure element per ton of fertilizer (gr/ton).
Nutrient concentration in fertilizers
Nitrogen (N) – the concentration of nitrogen in a commercial fertilizer is expressed as the percentage of pure N in the fertilizer, as grams of N in 100 gr of fertilizer.
Phosphorus (P) – the concentration of phosphorus in the commercial fertilizer is expressed as the percentage of phosphorus (pent) oxide (P2O5) in the fertilizer, as grams of P2O5 in 100 gr of fertilizer.
The relationship between pure phosphorus (P) and the oxide (P2O5) is:
1 Kg (pure) P = 2.3 Kg P2O5 (2.3 x the weight of P = the weight of P2O5).
Or: 1 Kg P2O5 = 0.44 Kg (pure) P (0.44 x the weight of P2O5 = the weight of P)
Potassium (Kali) (K) – the concentration of potassium in the commercial fertilizer is expressed as the percentage of potassium oxide (K2O) in the fertilizer.
The relationship between pure potassium and potassium oxide is:
1 Kg (pure) K = 1.21 Kg K2O. (1.21 x the weight of K = the weight of K2O).
Or: 1 Kg K2O = 0.832 Kg (pure) K. ( 0.832 x the weight of K2O = the weight of K)
Important !! Phosphorous units and Potassium units are the terms used by the industry and the farming community – these are not scientific units
The numbers that appear on a fertilizer’s formula express the concentration of the various nutrients (for both solid and liquid fertilizers) in percentage per unit weight. The world over, the main nutrients are listed in the following order: N-P-K (nitrogen, phosphorus, potassium).
Nitrogen: The first number on the left represents the concentration of pure nitrogen (N) in the commercial fertilizer, in percentage units.
Phosphorus: The second number represents the concentration of phosphorus (pent) oxide (P2O5) in the commercial fertilizer, in percentage units. In order to calculate the concentration of pure P (in %), multiply that number by 0.44.
Potassium: The third number represents the concentration of potassium oxide (K2O) in the commercial fertilizer, in percentage units. In order to calculate the concentration of pure K (in %), multiply that number by 0.832.
The chemical composition of a solid fertilizer
This example shows how the concentration of nutrients in the fertilizer is calculated:
Given: 100 Kg of “Gatit19 – 9 – 17” commercial solid fertilizer.
Nitrogen Phosphorus Potassium
19 Kg of (pure) N.
9 Kg of phosphorus (pent) oxide (P2O5) that are (0.44 x 9 =) 3.96 Kg (pure) P.
17 Kg of potassium oxide (K2O) that are (0.832 x 17 =) 14.14 Kg (pure) K.
Given: 100 Kg of “Shafir5 – 3 – 8” commercial liquid fertilizer (100Kg is about 85L)
5% 3% 8%
Nitrogen Phosphorus Potassium
5 Kg of (pure) N.
3 Kg of phosphorus (pent) oxide (P2O5) that are (0.44 x 3 =) 1.32 Kg (pure) P.
8 Kg of potassium oxide (K2O) that are (0.832 x 8 =) 6.65 Kg (pure) K.
Remember: Commercial fertilizers are marked as follows: The first number on the left represents the percentage (%) of (pure) nitrogen (N) in the fertilizer. The second number represents the percentage (%) of phosphorus (pent) oxide (P2O5) in the fertilizer. The third number represents the percentage (%) of potassium oxide (K2O) in the fertilizer.
Volume weight of liquid fertilizer solutions
This is an important characteristic of liquid fertilizer solutions. The volume weight represents the weight in grams per cubic centimeter of fertilizer solution (gr/cm³). 1 gr/cm³ = 1 Kg/Lt = 1 metric ton/m³.
The volume weight of a 21% solution of Ammonium nitrate is 1.28 gr/cm³.
Therefore in 1000 cm³ (= 1 L) there are 1280 gr (1.280 Kg) of ammonium nitrate.
In 1 m³ (1000 litres) there are 1280 Kg (1.28 ton) of Ammonium nitrate.
The two most common means to determine the volume weight of a fertilizer solution are:
The hydrometer: an easy to use instrument, it is inmersed in the fertilizer solution and the volume weight is read directly on its scale in units of gr/cm³.
By laboratory analysis with three replicates: the average weight of 10 cm³ of the fertilizer solution determined on an exact scale.
Important!! It is very important to measure the volume weight of the solution in order to calculate fertilizer dosage. Solid fertilizers are sold and invoiced by weight. Therefore all commercial quantities are quoted in kilograms or in metric tons. Liquid fertilizer, however, are metered / applied by volume, (in litres per unit area). Therefore it is important to know the volume weight of each liquid fertilizer source.
A 32% solution of Urean (urea–ammonium–nitrate) contains 320 gr (pure) N per Kg of solution, as calculated with the following formula:
Weight of fertilizer x % nutrient concentration/100 = Weight of nutrient in one Kg fertilizer
1000 gr fert. x 32 % N / 100. = 320 gr N / 1 Kg fert.
The volume weight of Urean 32% is quoted as: 1.30 gr/cm³ (1.3Kg/L).
Therefore: 1 litre of fertilizer solution weight 1300 gr (1.3 Kg /Lt) and therefore contains 416 gr (pure) N as calculated with:
320 gr N / Kg fert. x 1.3 Kg/ L = 416 gr N / L fertilizer.
Important!! Wherever the volume weight of a fertilizer solution is mentioned in this catalogue, its always given in units of weight per cubic cm (gr/cm³), (Kg/Lt) or (metric ton/m³).
* Farmers, agronomists and fertilier distributors may also use the terms “density” or “specific weight”.
The pH of the liquid fertilizer solution or solved solid water soluble fertilizer
The pH indicates the acidity or the alkalinity of the fertilizer solution, in a scale from 1 to 14. Where:
.pH = 7: neutral solution.
.pH above 7: alkaline solution.
.pH below 7: acid solution.
In the range of pH = 6.5 – 7.5 the solution is considered as neutral.
In the range of pH = 3.5 – 6.5 the solution is considered as weakly acid.
A pH below 3.5 is considered strongly acid.
The selection of a liquid fertilizer must take in consideration both its pH and the equipment employed for its application. Solutions used in fertigation through drip, micro-jet and micro-sprinklers (made wholly of plastic materials and no metallic components) may have a low pH, which aids in impeding the clogging of emitters with calcium and magnesium carbonates (CaCO3, MgCO3) that settle out whenever the irrigation water has a high pH and a high carbonate content. Acidulated irrigation water, at a pH of 6 is able to maintain 36.8 meq Ca/Lt in solution (737.5 mg Ca/Lt), while irrigation water at pH 7 dissolves no more than 7 meq Ca/Lt (140.3 mg Ca/Lt).
In order to avoid corrosion of fertigation equipment with metallic components (such as sprinklers, pivots, etc.) or of liquid fertilizers sprayers and injectors, only fertilizer solutions with a pH above 6 should be used.
Fertilizer solutions containing micro- elements should be maintained at a pH above 3.5, since chelates decompose at very acid (low) pH levels.
Even if the irrigation water is maintained in the pH range 5.5 – 6.5, the pH of the fertilizer solution does not have a long- term effect on the soil’s pH, due to the soil’s buffering capacity.
The color of solid fertilizers
Most of the solid fertilizers in shades of white, off-white or light beige color. However to the Gatit fertilizers a color can be added. This is done in order to distinguish different fertilizers or for identification of the fertilizer in the irrigation water.
The colour of the liquid fertilizer solution
Most fertilizer solutions are colourless, while some have a characteristic colour, as have, per example, solutions prepared with phosphoric acid. These fertilizers have a characteristic yellowish – brownish colour, depending on the concentration of phosphorus in the solution.
Fertilizer solutions enriched with various micro- elements have different colours, depending on the kind and concentration of these.
Turbidity of the liquid fertilizer solutions
Most fertilizer solutions are transparent and clear. Some components, however, make the solution to be somewhat turbid. Turbidity is a characteristic of the line of liquid fertilizers. Inbar fertilizer suspensions are always turbid.
The corrosivity of liquid fertilizer solutions
Corrosivity is a characteristic that expresses the degree to which fertilizer solution attacks various metals.
Very corrosive solutions: (with a pH below 3.5) Corrode all metals, including stainless steel.
Weakly corrosive solutions: (with a pH in the range from 3.5 to 6.0) Corrode iron and steel but do not attack stainless steel.
Non-corrosive solutions: (with a pH above 6.0) Do not corrode metals such as: iron, steel, stainless-steel, aluminum, bronze, etc.
The composition of a fertilizer solution determines its corrosivity. As a general rule, a strongly acid solution with a pH below 3.5 is considered to be very corrosive. Solutions with a pH above 3.5 are generally weakly corrosive or non- corrosive. Most fertilizer solutions containing phosphorous are corrosive, except for those specially prepared on the client’s request as non-acid. Acid fertilizer solutions containing chloride (Cl) are considered to be very corrosive; these solutions are prepared with Potassium Chloride (KCl).
Fitness for different fertilizer application techniques
The proper selection of the fertilizer must take the application method into consideration.
It is important to adopt the proper technology for the application of each line of fertilizers, according to its physical and chemical characteristics – alternatively, choose the correct fertilizer for the application equipment available.
Ignoring these recommendations may damage the application equipment. A corrosive solution (recommended for fertigation only) should never be applied with a spraying machine or banding equipment as this may destroy all of its metallic components in a very short time. Also introducing a fertilizer recommended for spraying only, should not be injected into the irrigation systema as it may clog both the filters and the emitters.a