Sports Ground Maintenance
Sports turf uses a lot more fertiliser and water than other green spaces. But why?
The explanation lies in the expectations of the playing surface. The surface must be able to withstand constant and often heavy impact. Most natural soils will compact under pressure. Compaction results in less pore space in the soil, leaving less room for root growth, oxygen supply, water-holding capacity and drainage.
To overcome these limitations of natural soils, various groups have developed specifications for resilient playing surfaces; for example, the US Golf Association (USGA). Soils manufactured to these specifications are resistant to compaction, maintaining good pore space for root growth and for nutrient and water uptake.
The down side to these soils is that the features that make them resistant to compaction also make them unsuited to holding either nutrients or water. But this is easily managed, as water and nutrients can be applied regularly. This brings us back to the observation that well managed sports turf uses a lot more fertiliser and water than other green spaces.
The underlying reasons are water-holding capacity and cation exchange capacity (CEC). The best soils for sports surfaces are effectively sand. CEC is the capacity of a soil to hold onto various nutrients (cations, or positively charged ions, such as ammonium, potassium, manganese and iron). Most of a natural soil’s CEC is due to clay particles and organic matter (OM). Sand has virtually none. So nutrients applied to such soils will wash through with the first rain or irrigation. And because sandy soils can hold very little moisture, frequent irrigation is necessary, exacerbating the problem of washing out the nutrients.
OM is an important component of natural soils, and with root turnover and turf growth and ageing, the OM content of a playing soil will gradually increase over time. This is good for the retention of nutrients but bad for the playing surface, as OM slows bounce, roll and running pace.
Why turf needs a lot of fertiliser
There are good reasons why the turf manager needs to maintain a high nutrient regime:
- High use and wear rates. For turf to recover as rapidly as possible from the high wear rates of constant use, soil nutrition must be as unlimiting as possible, with the right balance of nutrients. Consider a local council oval used all weekend, usually 2 or 3 days a week by schools and often every weekday evening by local clubs: it’s no wonder wear rate exceeds recovery rate, and the field shows bare soil.
- Low cation exchange capacity. Ironically, the better the field (i.e. the more sandy and forgiving of compaction it is), the more often it will need feeding, simply because sand has so little CEC to hold the potassium, ammonium, calcium and magnesium needed by the turf. In extreme situations such as A grade fields with very sandy USGA-type profiles, it is virtually hydroponic culture. Even weekly feeding is often needed.
- Low phosphorus fixation. In regular soils, the phenomenon of P fixation helps retain P in the profile and allow slow release to plant roots. However, in high-grade turf soils, which have so little clay and iron minerals to hold onto the phosphorus, frequent light applications are needed.
- Low organic matter and thatch levels. Organic matter provides CEC and a slow-release nutrient pool. Although some organic matter is necessary in soils, thatch build-up is a constant issue that affects playability of the field, usually slowing bounce, roll and running pace.
- To replace nutrients removed. Nutrients will leach down through the soil profile out of reach of the roots. You also need to maintain the balance between how much is taken out away (when you mow and remove the clippings) and how much is added (mainly as fertiliser). Further, this balance depends on how fast the plants are growing.
All these aspects mean turf managers must use what appears to be more fertiliser than other types of recreational spaces.
How to get the best out of your turf
As a general guide, SESL offers the following advice:
Don’t “fly blind”. You can’t see soil nutrient levels. By the time you see signs of deficiency in foliage (e.g. yellowing, slow recovery), you have lost precious time.
Very little of the health of turf and the factors underlying it is visible. Some nutrient imbalances show characteristic symptoms, such as leaf yellowing (typical of nitrogen deficiency) or reddening (typical of phosphorus toxicity), but most are not visible, or look like symptoms of other problems, or are masked by other symptoms, or are transient.
- Use yearly “full checkup” testing that includes pH, cation balance, and major, minor and trace elements.
- Use simpler and cheaper soil monitoring tests throughout the growing season. These check only N, P and K.
Use foliar analysis to inform the nutrient program during the peak of the season.
Use frequent split applications, perhaps up to 12 feeds over the season, plus weekly liquid feeding on the highest-grade surfaces.
As a general rule, high-use sports turf needs the following ranges of nutrients over the year (timing biased towards the peak season, of course):
- N 90–150 kg/ha
- P 20–50 kg/ha
- K 70–120 kg/ha
- Ca 20–50 kg/ha
- Mg 10–30 kg/ha
This is a very rough guide and depends very much on rainfall, wear rates, soil CEC and expectations of the turf surface.
Talk to one of our team about a tailored solution to your sports field, to keep it in peak condition all year round.
Camberato JJ. 2002. Soil fertility for turf managers. Clemson University.