Applying fertilisers

Too little fertiliser can result in a poorer effect than required and a lack of uniformity can cause patching, with missed areas growing more slowly than those impacted by fertiliser. This patching can result in a poor aesthetic quality and an even playing surface.

Over-application of fertiliser can cause excessive growth and there is a real risk of scorching the grass – especially when using quick-release mineral fertilisers.  There is also a cost implication associated with over-application.

There are many different makes of pedestrian and tractor-mounted fertiliser spreaders and it is prudent for the operator to fully familiarise themselves with how to calibrate the piece of kit they are using before commencing spreading.

Similarly, liquid fertilisers should be diluted at the manufacturer’s recommended rate and the sprayer operator should calibrate the sprayer correctly.  

Economic and environmental sustainability

When considering whether to use slow-release or quick-release fertilisers, the relative inefficiency of quick-release products should be taken into account. Quick-release fertilisers are typically much cheaper per bag than slow-release fertilisers. However, the spreading rate is typically higher than that of slow-release fertilisers and the period of release is far shorter. Therefore, from an economical point of view, using slow-release fertilisers can work out to be the best option.

If we take into account the inefficient nature of quick-release fertilisers, the probability that a good percentage of the nitrogen will be lost through leaching or atmospheric volatilisation and the increase in CO₂  emissions associated with extra applications of quick-release fertiliser, then the argument for using slow release fertilisers over large amenity areas as the most economic and environmentally sustainable way forward is very strong indeed.

Comparative cost of fertilising with quick- and slow-release fertilisers

The comparisons above show that, across one hectare, applying the same amount of Nitrogen using slow-release fertilisers is more cost-effective than with quick-release fertilisers. If we further consider that a good percentage of the nitrogen applied as quick-release fertiliser will be lost, then the advantages of using slow-release fertilisers increase still further with a better result being achieved for less cost in terms of product cost and the number of applications required. This principle is particularly important for local authorities when considering the economically and environmentally sustainable way of fertilising large public open spaces.

Fertiliser plans

To achieve the best results on high-value turf areas such as sports pitches and golf clubs, a bespoke fertiliser plan should be devised. This can be done in conjunction with any Fertiliser Advisers Certification and Training Scheme (F.A.C.T.S) qualified person, such as any of Germinal’s Technical Sales Representatives.

All fertiliser plans should begin with a broad spectrum soil analysis which will highlight any nutrient deficiencies and any issues with the pH of the soil. All fertiliser plans will be different and will vary according to soil type, the intensity of play or wear, and any budgetary constraints involved. As a rule of thumb, the amount of NPK applied to different turf areas per year can be summarised as follows:

There will of course be many ways to apply the required amount of fertiliser and this will depend upon personal preference and the machinery, equipment and manpower available to each individual situation. An example of a fertiliser plan for a high-intensity sports pitch is below.

Useful information

Fertiliser declarations

All fertilisers must be declared, by EU law, in a standardised way in order to enable easy comparison of the quantity of nutrients contained in different commercially available products.

Using potassium as an example, the material sulphate of potash, or ‘SOP’ is chemically known as potassium sulphate (K₂SO₄). However, the declaration on a bag of fertiliser might appear as ‘50% potassium-oxide’ (K₂O). This is the standard way of declaring potassium and does not mean that the bag of fertiliser contains potassium-oxide but is the equivalent quantity if the K was in the oxide form.

Occasionally, and particularly in soil and herbage analyses, nutrient contents are given in the elemental form (pure nutrient). The following conversion factors can be used to calculate either the elemental or the oxide form:

Elemental to oxide

• P to P₂O5: multiply by 2.29
• K to K2O: multiply by 1.21
• Mg to MgO: multiply by 1.66
• S to SO3: multiply by 2.5

Oxide to elemental

• P₂O₅ to P: multiply by 0.44
• K₂O to K: multiply by 0.83
• MgO to Mg: multiply by 0.6
• SO₃ to S: multiply by 0.4

Fertiliser Rate Calculations

Usually, a fertiliser recommendation is based on a nutrient per area basis and we need to understand how to translate this into a product per area basis.

Worked example:

• The recommendation for a sports field is for 50 kg N / ha (5g N / m²).
• To calculate the actual granular product required to supply this quantity of Nitrogen the OBAN formula is used:  (OBjective over ANalysis) x 100.
• Thus the rate of Floranid Permanent (15%N) to be applied is as follows:
• 50 (the objective) / 15 (the analysis) = 3.33 x 100 = 333 kg/ha
• The concentration of nutrients in fluid fertiliser may be expressed as kg nutrient per tonne of fertiliser (w/w basis) or more commonly as kg of nutrient per m³ (1000 l) of fertiliser (w/v basis). To convert from one to the other, it is necessary to know the specific gravity of the fertiliser.
• Concentration as w/v (kg/m³) = concentration as w/w (kg/tonne) x specific gravity.
• Taking the same example of 50kg/ha N requirement we decide to use a liquid fertiliser with 10% w/v N with a specific gravity of 1.2 w/v.
• Then the calculation is as follows:
• 50 (the Objective) / 10 (the analysis) / 1.2 = 417 l/ha