Environmentally friendly fertilising in turf horticulture

What do you think happens to all the fertiliser that is applied to turf? Most people would answer that it is absorbed by the grass and promotes green, vigorous growth.

This is not always true! Often turf plants may not be able to use fertilisers that have been applied because:

  • soil pH has 'locked nutrients out' and stopped them being absorbed by the plants

  • the plants already have a sufficient amount of that nutrient

  • soil compaction has inhibited the movement of fertiliser to the root zone

  • excessive irrigation or rain has washed the fertiliser past the roots of the turf.

Any fertiliser applied that cannot be used by the plant will move through the soil profile and contaminate the environment.

The two main nutrients responsible for most environmental damage are nitrates and phosphates. Both of these can leach into and contaminate underground water sources, lakes, streams and rivers causing detrimental effects to both humans and wildlife. Contamination of groundwater is a serious issue as some areas of Australia rely on underground aquifers for a large percentage of their drinking water.

Phosphates leaching into watercourses contribute to algal blooms that clog waterways and disrupt marine food chains. Not all soils, particularly sandy soils, have the ability to retain phosphorous. Before phosphorous is applied to turf, the soil should be tested to establish the current phosphorous levels and to determine the ability of the soil to retain phosphorous (Phosphate Retention Index or PRI). The PRI works on a continuum. Ratings of two or lower indicate a very poor phosphate retention whilst ratings over ten indicate the soil has a greater ability to retain phosphorous.

Leaching of nutrients into the water table can be avoided by:

  • testing soil to find out compaction and PRI

  • carefully monitoring irrigation volumes

  • tissue testing to establish plant requirements

  • the application of small amounts of nutrients often rather than large doses infrequently

  • applying fertiliser to turf leaves rather than through the soil.

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