Knowing your impact on the environment at large is a crucial element of turf care. With authorities claiming excess nitrogen from agricultural sources to be one of the main causes of water pollution in Europe, a scientific study was conducted to establish the leaching pattern of turf and hybrid sports surfaces.
Phosphorus, potassium and nitrogen are crucial elements for grasses to grow. Nitrogen is particularly important as it stimulates the overall growth and development of the grass, thereby ensuring thicker and longer blades as well as a denser and firmer turf that is less vulnerable and has better rooting. However, high concentrations can be a financial burden to the club and are harmful to people and nature. Nitrates and nitrogen that enter groundwater through leaching can make water unsuitable as drinking water and cause the excessive growth of algae in water systems. This affects the natural ecosystem and can lead to depletion of the oxygen in the water. This phenomenon, known as eutrophication, has negative consequences for biodiversity, fisheries and recreational activities. In 2000, the European Commission ratified the European Water Framework Directive in 2000 to stop this from happening. By 2027 latest, EU member states are expected to have established a chemically clean and ecologically sound surface water and ground water system. This inspired the Dutch industry organisation for Sports and Cultural Engineering (BSNC) to commission a study into the actual effect of the current fertilisation programmes used for sports turf, which mechanisms play a role in a possible washout, and what it is that can be done to reduce this leaching. They focused on hybrid turf surfaces in particular, as the popularity of this type of surface has been growing in recent years. “There is a clear difference between water and nutrient management on grass and hybrid sports surfaces,” explains Pleun Lok. He chairs the Hybrid Surfaces Working Group of the BSNC.
Three different test beds
The study group had 24 test beds constructed at Unifarm of Wageningen University and Research (WUR), the Netherlands. “A third of the test beds consisted of 100% natural turf, one third were stitched hybrid sports surfaces, and one third were backing-based hybrid turf sports surfaces. The different surfaces were built on subbases with M50 210µ (80/20 sand-peat) sand and with M50 300µ (80/20 sand-peat) sand. We allowed the grass three months to grow and to settle before we started with our experiment,” Lok continues. Each combination had a test bed that was fertilised with mineral and one that was fertilised with organic fertilisers for six weeks. “During that period, the 24 test beds were irrigated three times a week. The volume added depended on the volume that had evaporated, but the beds were more than saturated to stimulate a possible leaching.” In total, each bed received 173 mm of water over the six-week period. Three to four times a week, measurements were taken in order to keep track of the soil moisture and salt content in the bins. Once a week, the water that had gone through the structure was collected, as were the clippings. The fresh cutting was weighed before being dried at 70 degrees Celsius for 24 hours. After drying, it was weighed again to obtain the biomass. “This was all taken to an independent lab, where they established the nitrogen levels for both the collected water and the clippings. The clippings were also tested for the presence of carbon by means of LECO analysis,” explains Thomas Evers of Lumbricus. Evers supervised the research project and has translated the data into computer models that provide more mechanistic understanding and clarity regarding scalability.
Food for thought?
According to Lok, the results are reassuring. “The measured cumulative nitrogen leaching over six weeks was between 0.4 and 0.9 kg N ha. This is a factor 100 lower than the total added nitrogen of 64 kg per hectare. Therefore, we can safely say that no substantial nitrogen leaching was observed, neither in the natural grass nor hybrid sports grass surfaces, irrespective of the different sand textures that were used for the subbase.” The study concluded that the maximum nitrogen uptake in aboveground biomass over six weeks was 40 kg N ha. This represents a nutrient efficiency of 55% for organic fertiliser and 64% for mineral fertiliser. “We also didn’t witness significant difference in aboveground plant growth or hydrological properties between natural grass and hybrid fields.” The differences that was observed was a 12% difference in biomass production in favour of the beds that had been fertilised with mineral fertilisers. “This can be attributed to the fact that mineral fertilisers release nitrogen well within six weeks, while the nitrogen release from organic fertilisers happens over a six-month period.” The six week trial period proved to be too short to establish the contribution to biomass production by the latter.
The influence of sand
Another difference that was witnessed was that the biomass production for beds that had been constructed on top of a coarser textured subbase was less compared to the biomass production on the beds constructed on a finer sand. “A possible explanation is that a finer texture of the subbase keeps the top layer staying moist longer. This gives the fertiliser a greater chance to dissolve and thus release more nitrogen,” Evers points out.
In terms of leaching differences between the subbases with a coarser sand or those built with a finer sand when saturated, the BSNC study didn’t show any difference. “The hydrological properties, such as the moisture content at saturation, are the same for both textures. This means that the volume available for water storage is almost the same for both textures. When water is applied, it flows faster through the coarse than through the fine-texture sand, but the amount that flows out remains the same.” Lumbricus established that, of the 173 mm of water each bed received in total, 100 mm was absorbed by the plant, 33 mm [pms-restrict subscription_plans=”7998, 10994″]evaporated and 48mm leached out of the system. The 8 mm left is attributed to calculation differences.
Recommendations
The study has allowed the BSNC to come up with several recommendations. “First of all, it is recommended to map the uptake patterns of grass plants for specific field conditions. This can be achieved by measuring the hydrological properties of the soil and establishing a water balance based on the climatic conditions,” Lok points out. “Also, it will be critical to calculate the optimal timing and amount of nutrient application based on plant uptake and nutrient availability to minimise leaching.” The soil and climate conditions are essential to determine the potential nitrogen uptake by the plant. Lok also points out that the findings on the window in which different types of fertilisers release the nitrogen, emphasise the importance of accurate knowledge of the solubility curves of available fertilisers on the market. “Knowing how much a product releases over a certain period of time can better compensate for the differences between mineral and organic fertilisers.”
Last but not least, the study results also make it clear that the solubility and mineralization of the fertilisers differed from what was claimed by the suppliers. This deserves to be studied more in-depth. “We advise investigating this in representative field situations rather than laboratory environments as the mineralisation is dependent on variables such as temperature, pH, and soil moisture.”
Possible follow-up
Martin Brummel, groundsman at the training centre of Ajax FC in Amsterdam, sat on the panel for this study. He is pleased with the outcome. “I am very pleased to know that the fertilisers remain in the field and don’t leach out into the ditch, as this was a concern we had when we decided to invest in seven stitched hybrid surfaces,” he says. The authorities in Amsterdam are very strict on water quality. “As hybrid surfaces are increasingly being viewed as a solution over a full-synthetic turf surface, it is good to have a better understanding of the effectiveness of fertilisers. However, to be successful, much depends on the technical knowhow of the person who is responsible for the pitch. For clubs at grassroots level that don’t have the budget to appoint a dedicated groundsman, I would advise embracing the expertise of independent external consultants or the companies that can assist with drafting fertiliser programmes.”
Andre Wolbrink, an agronomist at sports field constructing company Greenfields, also sat on the panel. Familiar with the results, he now looks forward to a possible follow-up study. “The idea is to apply the computer model on the various subbases that we typically use for a football surface in the Netherlands in order to be able to predict the nitrogen uptake or leaching behaviour of a particular subbase,” he says. “These models could also help to predict when one needs to fertilise again.” It is highly likely that studies conducted by the various suppliers of fertilisers on the behaviour of their product, will be included in the follow-up study.
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