Unusual Turf Problems

An effective programme is tailored to the needs of the turf, and incorporates ongoing assessments and evaluations of its health, vigour and usage.

In northern New Zealand, sports fields and golf courses are increasingly converting areas from the traditional cool season turf species (such as ryegrass and fescue/browntop) to the warm season grasses (Kikuyu, common couch and hybrid couch). With this shift, turf managers are having to become familiar with the differing management regimes warm season grasses require.

Starting point

Conducting a soil test is the first step when reviewing fertiliser applications. For sand-based turf, testing should be done annually; for soil-based turf where leaching potential is lower, the testing could be extended to 2-yearly intervals. The test helps determine the fertility requirements (other than nitrogen) which have a huge influence on the persistence of the particular species/turf and eliminates the risk of purchasing and applying nutrients which are not required. Testing also allows turf managers to produce a Nutrient Management Plan and ensures they comply with the local district and regional plans.

Figure 1: Excessive clippings on high density turf due to high nitrogen fertiliser application rates (i.e. maintenance-only inputs were required).

Playing quality objectives

The purpose of fertiliser applications is to maintain healthy, dense turf throughout the playing season. For winter sport, no recovery of warm season turf is possible through fertilisation due to low temperatures. Hence, the turf vigour and density achieved through summer is crucial to ensuring a high quality, winter surface − unless overseeding with ryegrass is carried out. Selection, timing and application of fertiliser will be influenced by the growth stage of the turf, the soil type and the desired outcome. In comparison to a golf fairway, well-used football, rugby and rugby league fields are going to require higher rates
of fertiliser and application frequency to promote recovery from wear.

Figure 2: Low turf density requires frequent, high inputs of nitrogen to achieve turf cover.

Figure 3: Very low density turf at the end of winter play.  Re-turfing or stolonising is required.

Information gathering

No matter the sport, a turf manager needs to ask the following questions when preparing a fertiliser plan for the coming season:

  1. Which nutrients do I need to apply based on soil testing?
  2. How long is the growing season, i.e. will any fertiliser application actually promote turf growth?
  3. Does the turf require recovery after winter/summer sport, i.e. is there sufficient turf density already present at the beginning of the summer or winter season?
  4. How much use does the turf receive when it is actively growing?
  5. How much use does the turf receive while dormant? 6. What is the developmental stage of the turf?

Correct inputs

Nitrogen is the most important nutrient for the growth and development of turf, followed by potassium and phosphorous. Recommended nitrogen application rates for couch grass are in the range of 180 − 300kg/ha per year, varying according to the use of the turf, climatic conditions and the required growth rate (see Table 1). The appropriate form of fertiliser chosen to supply the nutrients will again be dependent on the required growth rate, expected use and the budget. There is the option of granular slow or quick release, compound fertilisers containing N-P-K, or soluble fertilisers containing single nutrients. Liquid fertilisers are also a consideration for even application of low nutrient rates over large areas.

Figure 4: Low density turf requires high rates of nitrogen and potassium applied frequently in spring until full density is achieved. It can thereafter thrive on maintenance rates (30kg/ha/month of nitrogen).

Figure 5: Medium density turf requires medium nitrogen application rates, fortnightly, until full cover is achieved; maintenance inputs thereafter.

Straight, quick-release forms of nitrogen (as found in urea and sulphate of ammonia) are recommended where rapid growth response is required to re-establish full turf cover.  Slow release forms, also known as controlled-release fertilisers, may be useful for maintenance level inputs applied at 2-monthly or greater intervals.

If we consider the Auckland region in a year of average temperatures and rainfall, the period of active growth for warm season grasses will be from September – February. This would mean that applications would fall into the range of 30 − 50kgN/ha/month. Potassium would be applied at a rate based on a 0.5−1:1 ratio with the nitrogen, while phosphorous rates would be determined and applied based on the soil test results.

The best time to assess turf and determine the required rate and frequency of fertiliser applications is at the start of the spring (before summer use commences). Guidelines on fertiliser rates are outlined in Table 2. If the turf is a dense and continuous sward, the lower rate of the nitrogen range and frequency of applications is recommended. Higher rates would produce excessive growth, resulting in more frequent mowing − or if mowing is scheduled weekly, there will be clippings left on the surface (see Figure 1). If the turf has low-to-medium density, then high rates of nitrogen should be selected and applied frequently until full cover is achieved; thereafter, fertiliser inputs can be reduced to maintenance levels.

Throughout summer, the turf should be re-evaluated at regular intervals, with adjustments made to fertiliser inputs to ensure full turf cover is kept or achieved through to autumn. It is important, prior to dormancy, to maintain nitrogen inputs to encourage development of rhizomes and the root system. It is the storage within these structures that ensures good spring green up and bud development as the turf comes out of dormancy. Insufficient rates of nitrogen fertiliser in the growing season will either result in never achieving full turf cover while in use, or loss of turf cover from use. The net, long-term effect of inadequate nitrogen fertiliser will be a gradual decline in the turf sward, as there’ll be insufficient rhizome development to ensure recovery after each winter. Under such a regime, it could only take a couple of years for the warm season grasses to completely disappear out of the turf sward.

Needs – based programmes

In conclusion, there is no set quantity of fertiliser that can be prescribed for yearly applications when aiming for dense, healthy turf. As with all turf management tools, the fertiliser programme must be based on the ongoing assessment and evaluation of turf health, vigour and usage requirements. Should you require further information or assistance with the preparation of fertiliser programmes, interpretation of soil test results, or forming a Nutrient Management Plan for your facility, please contact your local NZSTI agronomist.

Figure 6: Re-turfing bare ground.

Everett Darlington

Everett Darlington

Agronomist

New Zealand Sports Turf Institute