Turf Fertilisers

What is a fertiliser?

A fertiliser provides one or more essential plant nutrients to aid growth and health and can be applied to the turf surface or rootzone. The main fertiliser nutrients applied to turf are Nitrogen, Phosphorus and Potassium, followed by Iron and occasionally Magnesium.

Why apply fertilisers?

Besides ensuring that adequate supplies of nutrients are available to the grass plant to aid it in making healthy and strong growth, there are other particularly important reasons why sufficient nutrients need to be applied to turf :

  1. The density of the sward can be increased.
  2. Desirable grass species can be encouraged, whilst less desirable grass species and weeds can be discouraged. This can be achieved by using different types of fertiliser which have varying effects on soil pH.
  3. The sward's ability to withstand wear and recover quicker from use is enhanced.
  4. The colour and visual appearance of the sward can be improved.
  5. A more uniform grass sward, which is without the presence of weeds, can be achieved.
  6. Root growth can be improved.
  7. A sward which has an improved ability to withstand the vigours of drought, cold and harsh weather.
  8. A more disease resistant sward is also produced.
  9. To provide a sward which produces a good playing surface.

General effects of fertilisers

Different fertilisers can affect the sward content in different ways. For example, alkaline acting fertilisers encourage coarser grasses, weeds and diseases as well as the production of a softer more easily worn surface: This is an important consideration in fine turf situations. The over use of organic and controlled release fertilisers can also produce a similar effect.

Acidic acting fertilisers encourage fescues and bents and reduce weeds, worms and annual meadow grass, as well as producing firmer surfaces. However, they can also discourage perennial ryegrass and smooth stalked meadow grass, which would be detrimental on a winter games pitch and creeping bentgrass on some golf greens.

Excessive acidity is especially undesirable as it results in a thin, patchy sward that is easily worn and produces a poor playing surface.

In deciding which fertilisers to use, it is important to consider the types of grasses which are to be encouraged for the area in question as well as the existing ground conditions, e.g. soil pH, soil texture and available nutrients.

Fertiliser nutrients

Nutrient content in either a fertiliser bag or for a fertiliser programme can be expressed in a number of ways :

  • Nitrogen is expressed as its chemical symbol N.
  • Phosphorus can be expressed as either its chemical symbol P or as phosphate P2O5.
  • Potassium can be expressed as either its chemical symbol K or as potash K2O.
  • Magnesium can be expressed as either its chemical symbol Mg or as magnesium oxide MgO.
  • Iron is expressed as its chemical symbol Fe.

It is important to ensure the method of expression is clearly stated, otherwise the amount of nutrient being applied may be incorrect. For example :

A nutrient programme is implemented which says to apply a fertiliser with a 10% phosphorus content. This should mean exactly what it says, however, often the terms phosphorus and phosphate are used very imprecisely.

Thus,if a 25kg bag of fertiliser is supplied with 10% of phosphorus (P), it will contain 10% of P, i.e. 2.5 kg. If however it contains 10% of phosphate (P2O5), it will contain just 4.37% of phosphorus, i.e. 1.09kg. Obviously quite a difference to what is planned.

It is quite easy to determine the difference between the expressions used because the figures are worked out using atomic masses.

e.g. Phosphorus

There is 100% of P in the expression P. However, how much P is there in P2O5 ?

[The atomic mass of 'P' is 31, therefore for 2 x P it is 62; whilst the atomic mass of 'O' is 16, therefore for 5 x O it is 80. The total atomic mass for P2O5 is therefore 62 + 80 = 142].

  • The P content in P2O5 is 62 ÷ 142 = 0.437, (or 0.437 units of P to 1 unit of P2O5 ) which is the same as saying that there are 142 ÷ 62 = 2.29 units of P2O5 to 1 unit of P. (i.e. 10% of P in a 25kg bag contains 2.5 kg of P (surprisingly!), but expressed as phosphate this is 2.5kg x 2.29 = 5.725 kg

Exactly the same process is carried out for Potassium (K = atomic mass of 39) and Magnesium (Mg = atomic mass of 24) as follows:

  • K in K2O : (2 x 39) + (1 x 16) = 94; Thus, 78 ÷ 94 = 0.83 units of K to 1 unit of K2O; or 94 ÷ 78 = 1.21 units of K2O to 1 unit of K. [e.g. In a 25 kg bag of fertiliser, a 10% content of K2O (2.5kg) provides 8.3% of K (2.075 kg)].
  • Mg in MgO : 24 + 16 = 40; Thus 24 ÷ 40 = 0.6 units of Mg to 1 unit of MgO; or 40 ÷ 24 = 1.66 units of MgO to 1 unit of Mg. [e.g. In a 25 kg bag of fertiliser, a 10% content of MgO (2.5kg) provides 6% of Mg (1.5 kg)].

Fertiliser analysis

Fertilisers contain two or more elements, which are combined together as chemical compounds. For example, Ammonium Sulphate is a combination of Nitrogen, Sulphur, Hydrogen and Oxygen and has the chemical formula (NH4)2SO4.

Using the atomic mass of each element it is possible to calculate the percentage masses of any of the elements in this fertiliser. The main element for turf is Nitrogen, and this is what will be used as an example:

Element Symbol Atomic mass Quantity Total atomic mass
Nitrogen N 14 2 28
Hydrogen H 1 8 8
Sulphur S 32 1 32
Oxygen O 16 4 64
        132

The percentage of Nitrogen within this compound is therefore : (28 ÷ 132) x 100 = 21.2 %.

This is what the pure salt contains, however, with minor impurities which occur in the manufacturing process, the commercial product typically contains about 20.5% Nitrogen.

 

The percentages of other plant nutrients in other inorganic fertilisers can be arrived in this manner, although there can be a number of different figures quoted for main and other nutrients depending upon the levels of impurities present within the source and manufactured product. When dealing with organic fertilisers and manures the problem is more complex due to the slightly variable nature of organic material and a typical range of analyses is normally given.

Types of fertiliser

1. Organic

This material is derived from a previously living organism, e.g. dried blood, bone meal or a synthetically produced material containing carbon, e.g. urea. This latter category is sometimes classed on its own within non-carbon based inorganic, synthetically produced material as the product was not previously alive.

Organic fertilisers generally release their nutrients at a slower rate than inorganic fertilisers.

2. Inorganic

These types of fertiliser can be either mineral, e.g. superphosphate, or synthetically produced, e.g. ammonium sulphate, and have a relatively quick rate of nutrient release.

3. Controlled Release

These are specially manufactured materials that have a low water solubility (e.g. ureaform) and/or applied coatings to reduce the release rate of the nutrients (e.g. sulphur coated urea, Didin). Generally these fertilisers produce a slow release of nutrients over a period of 8 to 14 weeks, or longer. These fertilisers do contain a variable amount of water soluble nitrogen which has a fairly quick release rate and this part is therefore similar in response to inorganic fertilisers.

Forms (formulations) of fertiliser

1. Straight

This supplies one main nutrient, e.g. N, P or K. An example of a straight fertiliser is ammonium sulphate supplying Nitrogen.

2. Mixture

This results from the physical mixing of at least two fertilisers and may contain all the main nutrients. The mixture may also be a combination of two or more fertilisers supplying the same nutrient, e.g. hoof and horn, dried blood and ammonium sulphate all supplying Nitrogen.

3. Compound

This is a fertiliser which includes two or more main nutrients and results from a chemical process which combines the nutrients and is only produced commercially. This is the most common form of fertiliser applied to turf.

Turf fertilisers can be supplied as either powder, granular, mini-granular, crumbs, prills or liquid.

 

Fertiliser sources

Key : Type : I = Inorganic, O = Organic, CR = Controlled Release ; Nutrient : S = Sulphur, Ca = Calcium.

Source Type % of Main nutrient Other nutrients Comments
Nitrogen (N)  
Ammonium Sulphate I 20.5 24% S 10-14 days for conversion to nitrate. Acidic reaction. A typical component of some fine turf 8:0:0 fertilisers.
Ammonium Nitrate I 34.5 n/a Mainly used as a component of winter sports pitch compound fertilisers : It has too high a nitrogen content for fine turf situations which would result in severe scorching of the turf. It has a slightly acidic reaction and is quick release. It is sometimes used as a liquid feed on high sand content golf greens containing creeping bentgrass.
Nitro-Chalk I 15.5-28 Ca This is a mixture of calcium carbonate and ammonium nitrate in varying proportions. A common mixtures produces 20.5% N. It is quick acting and soluble, producing an alkaline reaction.It can be used for general turf areas with a highly acidic soil.
Urea (Carbamide) O 46 n/a First synthesized in 1828 and now produced by heating CO2 and ammonia under high pressure.
Quick release : 7-10 days. Initially a neutral , followed by a slightly acidic reaction. Normally applied as a liquid feed, giving a rapid green up effect. Too much reliance on these types of fertilisers (i.e. urea based) encourages annual meadow grass and disease attacks.
Dried Blood O 10-14 ~0.8% P Nitrate production begins after 4-5 days: It lasts for about 2-2½ months. It is readily soluble in water and produces a neutral reaction. It improves drought resistance on fine turf. A typical component of some 8:0:0 fine turf fertilisers.
Hoof & Horn O 12-14 ~0.3% P The fineness of the ground material affects how long it will last, but that which is used on turf will last some 3 months. It produces a neutral reaction and improves drought resistance on fine turf. A typical component of some 8:0:0 fine turf fertilisers.
Ureaform(aldehyde) CR 38 n/a This is obtained by the polymerisation of formaldehyde and urea. It is very slow release, over about 6-7 months, with about 70% insoluble N. It has a neutral reaction.
Some commercial products have a release rate lasting 12-16 months.
IBDU
(Isobutylidene diurea)		 CR 32 n/a A condensation product of urea and isobutraldehyde with a slow dissolution of some 3-4 months. It produces a neutral reaction.
Floranid 31:0:0 with 12-14 week release rate.
Sulphur Coated Urea CR 32 S This is urea with a sulphur coating and produces a slightly acidic reaction overall.
e.g. Super N 24:0:0 or Mini-Gold 31:0:0.
Methylene Urea CR 40 n/a This is a combination of quick release and slower release (ureaform), water insoluble nitrogen. It produces a neutral reaction.
e.g. Supaturf 'Intafaze' 20:5:10 (which includes 7% M.U.), with a release rate of up to 10 weeks and a small amount up to 3-6 months.
Triazone CR various n/a Formed by the reaction of urea, formaldehyde and ammonia with a similar response to urea.
e.g. Headland N-Sure 28:0:0
Resin coated fertilisers CR various n/a These dissolve slowly with the release rate being dependant on the thickness of the coating. e.g. Sierrablen mini 22:3:7 , or Osmocote 39:0:0; with a release rate of some 5-6 months.
Didin
(Dicyandiamide) treated		 CR various n/a A bacteriostat that slows down the conversion of ammonium to nitrate.
e.g. Miracle Professional 14:3:7 (Ammonium sulphate coated), with 8-12 weeks release rate.
Phosphorus (P)  
Superphosphate I 9 21% Ca & 11% S The best source for turf. A neutral effect on the soil.
Ammonium Phosphate I ~ 22 11% N Used within compounds. Slightly acidic reaction.
Bone Meal O 10 4% N Traditionally applied prior to turfing. Slightly alkaline effect on the soil.
Potassium (K)  
Potassium Sulphate I 45 18% S Mainly used as a straight or in a mixture, as it stores better than potassium chloride.
Potassium Chloride (Muriate of Potash) I 52 n/a Commonly included within compound fertilisers as the potassium source.
Magnesium (Mg)  
Magnesium
Sulphate (Epsom salts)		 I 10 13% S Magnesium deficiency in turf is rarely a problem, however, very high sand content areas may require magnesium fertiliser input.
Iron (Fe)  
(Calcined) Sulphate of Iron I 20-25 11% S Widely used on fine turf, acidifying the surface, reducing weeds, worms and disease and improving colour without the need for nitrogen fertilisers. Overuse leads to a deterioration of the sward and should be used with caution on perennial ryegrass dominated swards.