Understanding Fertilizers

During the course of an average year, the cutting and grooming of the turf grass will remove nutrients from a bowling green. The removal of grass normally amounts to between 1.1 and 1.4 tonnes of dry matter. This represents the removal of approximately

  • 50 kg of Nitrogen
  • 3 kg of Phosphates (Phosphorus)
  • 35 kg of Potash (Potassium)

In addition to the above, the removal of other necessary elements such Sulphur, Calcium and Magnesium occur, and these are removed more or less in the same quantities as that of the amount of Potash.

The micro-elements comprising of Zinc, Boron, Molybdenum, Iron, Manganese and Copper are only removed in very small quantities.

Consequently in order to maintain a healthy turf grass, these nutrients need to be replaced.

Generally speaking the nutrients required by turf grass can be classified into three groups as follows:

  • Major nutrients.
  • Secondary nutrients.
  • Micro nutrients.
Major Nutrients
  • Nitrogen (chemical symbol N)
  • Phosphorus (chemical symbol P)
  • Potassium (chemical symbol K)
Secondary Nutrients
  • Sulphur (chemical symbol S)
  • Calcium (chemical symbol Ca)
  • Magnesium (chemical symbol Mg)
Micro Nutrients

Heavy metals

  • Iron (chemical symbol Fe)
  • Manganese (chemical symbol Mn)
  • Zinc (chemical symbol Zn)
  • Copper (chemical symbol CU)

Non metals

  • Boron (chemical symbol B)
  • Molybdenum (chemical symbol Mo)

Beneficial nutrients

  • Aluminium (chemical symbol Al)
  • Sodium (chemical symbol Na)

The majority of fertilizers used by greenkeepers to feed their greens contain the three major pure elements.

These are:

  • Nitrogen
  • Phosphorus
  • Potassium

Fertilizers are often referred to by a three digit code i.e. 10:1:5.

The first digit always refers to the nitrogen element, the second relates to the phosphorus element and the third digit refers to the Potassium element. In the example above (10:1:5) the ratio of Nitrogen contained is 10 parts, Phosphorus is 1 part and Potassium is 5 parts.

Fertilizers normally indicate on the bag of fertilizer the quantity of active ingredient that are contained in the bag i.e. 10:1:5 (50).

Thus for example if a bag of fertilizer is shown as having an active ingredient content of 50% and weighs 50 kilograms, then the actual amount of active ingredient is 25 Kilograms (50 x 50%). The remainder of the bag of fertilizer contains inert carriers which assist in the application of the fertilizer.

Using the example shown above one can work out the actual quantities by weight of Nitrogen, Phosphorus and Potassium contained in the bag of fertilizer.

To do this, simply add the values of the digits contained in the code i.e. 10 + 1 + 5 = 16.

If the active ingredient ratio is say 40%, then we know that the total weight of the active ingredients is 40 % of the total weight of the bag of fertilizer, and in the case of a 50 kg bag this would be 50 kg x 40/100 = 20 kg.

Having determined the total weight of active ingredients (20 kg), we can now work out what weight each component of the fertilizer is.

For example of a bag of fertilizer shown as 10:1:5 with an active content of 40%, that weighs 50 kg, the following calculation can be done:

Nitrogen    10 / 16 x (50 x 40 / 100)   =    12.50 kg
Phosphorus  1 / 16 x (50 x 40 / 100)    =     1.25 kg
Potassium   5 / 16 x (50 x 40 / 100)    =     6.25 kg
                            -----------
Total weights of active ingredients     =    20.00 kg

Therefore if a greenkeeper applies the full 50 kg bag of 10:1:5 (40) fertilizer to a green, they would be adding 12.50 kg of Nitrogen, 1.25 kg of Phosphorus and 6.25 kg of Potassium.

As bags of fertilizers are often sold in various weights using the above formulas allows the greenkeeper to work out exactly what quantities of the three major elements they are putting onto a green.

In general the larger the bag of fertilizer bought, the lower the unit price is. For example 10 10kg bag will cost R150.00, a twenty kg bag will cost R250.00 and a fifty kg bag will cost R500.00 the unit cost for each is:

10 kg bag   R150 / 10 = R15.00
20 kg bag   R250 / 20 = R12.50
50 kg bag   R500 / 50 = R10.00

It is often the case that a greenkeeper does not wish to apply a full bag of fertilizer to a green in one application, but wishes to apply a part bag. In such cases it is still important that the greenkeeper knows what quantities of Nitrogen, Phosphorus and Potassium they are applying. In such cases a further calculation needs to be done.

Having determined the weight of active ingredients contained in a bag of fertilizer, if the greenkeeper applies half of a 50 kg bag of 10:1:5 (40) to the green, the actual active quantities of pure ingredients are as follows:

Nitrogen    (10 / 16 x (50 x 40 / 100))   x  25 / 50  =   6.25  kg
Phosphorus  (1 / 16 x (50 x 40 / 100))    x  25 / 50  =   0.625 kg
Potassium   5 / 16 x (50 x 40 / 100))     x  25 / 50  =   3.125 kg
                                    -----------
Total weights of active ingredients                   =    10.00 kg

The Fertiliser program

A balanced fertiliser program must be followed for the duration of the year. As a general rule fertilizers should be applied at a similar rate as the removal of the grass, but the greenkeeper should also take into account the following factors:

  • The active turf grass growth period
  • Renovation time
  • Wear and tear of the turf grass

Apart from the three major elements (Nitrogen, Phosphorus and Potassium) the other required elements will need to be applied.

The best way of ensuring that the correct quantities of elements that are need to be added to the Bowling Green, is to take soil samples (at least one month after last application of fertilizer), submit them to a lab and then have them analysed to create a fertilizer application program.

There are however, other considerations that should also be taken into account are when using fertilizers. These are as follows:

  • When LIME is applied to a green one must exercise care not to use NITROGEN too soon as this will create ammonia gas on the surface which could be fatal.
  • Records must be kept at all times of work and chemicals used on the green and surrounds.
  • To ensure that a program is to work correctly pH levels are to be checked on a regular basis to ensure the correct balance is kept.
  • Fungicide should be sprayed separately to the program as when added it tends to push up the acidity level at the time of application.
  • It must be remembered that towards the end of the growing season the amount of POTASSIUM should equal that of NITROGEN.
  • The composition and nature of the water being applied to the greens. It is important to note that most borehole supplies contain various trace elements that have either leached through the soil after surface application or those that occur naturally in the bedrock containing the water source, and have been dissolved into the water source being extracted.