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May 13, 2022
Capillary Hydroponics, 11320 FortuneCircle, Suite G23, Wellington, FL 33414,USA
Martin Sternberg, Capillary Hydroponics,11320 Fortune Circle, Suite G23,Wellington, FL 33414, USA. Email: martin@capillaryconcrete.com
Natural grass areas in high-traffic and stress locations are being converted into artificial grass by inconsistent moisture conditions in root-zone and poor grass conditions. As an alternative solution to this method, natural grass was planted instead in a washed sand without organic matter and with a constantly moving water table and no overhead irrigation. Water consumption and surface quality after heavy machinery exposure was measured. A significantly increase in the potential for traffic and play was observed, along with water savings of up to 85% compared with normal overhead irrigation amounts for similar surfaces (golf course tees).
The global artificial grass market is expected to reach US$6.5billion by 2026 and is quickly becoming a standard solution for high-traffic and high-value surfaces, effectively outcompeting natural grass. Despite the obvious environmental negative effects, such as include very low recycling practices (–10% currently), micro plastic pollution of ecosystems, and the high CO2 footprint, plastic grass is currently winning.
The main reasons for switching from natural grass to artificial are mostly the physical limitations of the ground beneath the grass. These limitations cause the areas to be unusable more than 25% of the time or require too much maintenance compared with artificial grass. With the invention of a new inorganic building material (Capillary Concrete), large-scale hydroponic grass areas can be built [CapillaryHydroponics (CH)] with high infiltration and load-bearing capacity.
Capillary Hydroponics is based on hydroponic growing principles and splits the grass area in two equally large areas, where one side acts as storage for water but the other is empty and the roots are exposed to the air. By reversing the flow of water several times per day, the ground water levels constantly shift and a true hydroponic system is created. The unique material Capillary Concrete is used to guarantee an absolute flat surface that does not create as well-defined a perched water table as the gravel in a United States Golf Association (USGA) method but still provides plenty of porosity for air circulation. Water is moved through a special basin and powered by an air pump and then gravity-fed to each area.
Deep oxygenation in the root zone has always been a problem on natural grass fields, since carbon dioxide accumulates in the air-filled pores in the root zone profile over time as grass roots grow (Figure 1). One of the problems is that carbon dioxide molecules weigh 1.34 times more than the oxygen molecules and thus are difficult to displace. The most effective way to emit carbon dioxide and reach an optimum level of oxygen in the air-filled pores of the root zone is to extrude carbon dioxide with a waterfront on a regular basis, imitating the natural growing conditions in sandy soils near coastlines with a fluctuating ground water table affected by ocean tidal movements (Figure 2).
With this method, we aimed to resolve the following problems that occur in natural grass areas:
The CH system does not rely on the root zoneťs inherent moisture holding capacity for supplying enough moisture to plants. This has the beneficial effect that superior hydraulic conductivity can be achieved without drying out the plantsand without excess irrigation. The levels of carbon dioxide are also minimized, as oxygen is introduced several times per day and the porosity of the soil is higher. There is also no leaching, as this is a closed system, with filters at the evacuation pipe in cases when precipitation is greater than the holding capacity of the system. The main benefits lead to greater accessand more wear tolerance. More hours of using the field result in a greater return on investment than regular natural grass fields.
This particular tee (Hawks Landing Golf Course, Orlando,FL, back tee on Hole #11) has been re-grassed several times in the past years, with new bermuda-grass [Cynodon dactylon(L.) Pers.] sod being placed almost on an annual basis over the past 10 yr. The tee is small and in a shaded location and was built with a USGA root zone material, but with the frequent summer rains, it regularly became soft and did not perform well under traffic and mowing equipment.
The tee was rebuilt with the CH system, for which a liner was placed on the subsoil and the area was divided into two separate “pools” with a basin and pipe connecting both (Figure 3). The root zone material is a more open sand without any organic content (Figure 4).
Capillary Concrete was used as a base for the sand in the system, a material that has a rating in ASTM C39 tests of over 70.31 kg cm–2 (1,000 lb inch–2), creating a durable, long-term base. Capillary Concrete is a special pervious concrete made from cement paste and polymers mixed with 2 to 10 mm gravel, which has an approximate porosity of 20%.Water is pumped with air-lift pumps from one compartment measuring 600 mm in diameter and 1,050 mm high to another basin, alternating at 2-h intervals. The basins are located near the edge of the grass area, with an equal distance to the center of each area. The air-lift pumps move 5 to 20 m3 of water per cycle depending on size of the solar panel and air pump. With a 50-W solar panel and a linear air pump of 15 L min–1, the water volume that can be moved is approximately 2.5 m3 h–1.The total water consumption was measured and recorded (see Figure 5). The total water consumption was compared with a tee of similar size in a nearby location and the average of the golf course’s watering schedules for tees (4 mm d–1), and the result was a water reduction of approximately 85% (Figure 6).
All fertilizers were applied to the water in the basin, which resulted in minimum leaching because it is a closed system.Every hydroponic cycle provides at least 10 mm of water to the root zone, and the cycle reverses every 2 h. The slow movement of the waterfront is an advantage, as it reduces the preferential flow and ensures full emptying of the available pore spaces. Depending on the weather and time of year (the air-pump runs on a solar panel and batteries), an average off our to six cycles per day is normal. The greatly increased gas exchange in the air-filled pores is also improved by the fact that the Capillary Concrete layer and the gravel beneath has about 20% porosity, with the spaces mostly filled with air, which is also pushed up through the root zone in each cycle.
Thanks to the open growing medium, the drainage has been easy to secure and the hydroponic system supplies enough moisture to promote healthy grass. Instead of the previous years’ sod replacement, about 100 m2 of sod has been saved at a cost of US$450. The tee has not been closed for a single day in 3 yr as opposed to previous years, where rainfall of more than 10 mm in a single event required at least 1 d of closure.
In Helsingborg, Sweden, a newly constructed public park is situated in the center of the city outside the new Congress Center and Clarion Hotel (Figure 7). This park is built to take a lot of traffic and be used by everyone. Frequent events and concerts with thousands of people attending is the norm, and the city planners were looking for an option other than artificial grass, as this contradicts their philosophy of a sustainable city.
Normal natural grass areas are often rebuilt after major events because of severe damage by heavy machinery and traffic. Compaction of wet root zones and a lack of oxygen when the ground is covered by sheeting often causes a grass sward to fail, and the solution is often to re-grass or replace the area with artificial grass. Instead, here, the root zone was built without any organic matter and with a washed sand that resists compaction very well (Figure 8). Water is circulated from below, back and forth from each section of the hydroponic system on this large 1,300-m2 natural grass area. The grass was established by seeding in the early summer of 2021. In August and first half of September, the weather was warm with hardly any precipitation. The water usage, with evapotranspiration of 3 mm d–1 was down 67% compared with a golf course tee.
During the fall, several heavy rainstorms passed through and, in1 wk, over 125 mm fell on the lawn. In the midst of this rainfall, after 3 d of almost constant rain, a stress test was conducted to assess the turfťs ability to withstand traffic and heavy machinery. A vehicle weighing 1,750 kg was driven on the grass back and forth for 30 min without any detrimental tracks or visible damage. The area was able to handle every single rainfall event during the week without flooding on the surface, equaling a percolation rate of above 50 mm h–1. The surface did not need to be closed during the rain, although similar natural grass surfaces in the city were closed for 3 to5 d in this particular week and were flooded +15 mm h–1 had fallen.
The system comes with a complete Internet of Things solution, in which sensors in the basins register water temperature, pH, dissolved oxygen, salinity, and electrical conductivity. The information is sent to the cloud and processed on a website for easy access and control. In Figure 9, data are displayed, showing the different cycles of water pumping between the compartments of the basin. This chart is from a day in December and is publicly available online. The chart shows the changes in parameters with the watering cycles, as the parameters are only measured in one of the compartments of the basin.
In conclusion, this new root zone construction method shows promise for maintaining high-quality natural turf grass surfaces with less water in areas of high traffic, providing a viable option to artificial grass.
We thank Bert Sandell (Research Consultant Capillary Concrete AB); Hawks Landing Golf Club, OR; and Helsingborg Stad, Ångfärjeparken for help with this research (https://www.youtube.com/watch?v=8Nvle4ZFQoM).
Martin Sternberg, Certified Golf Course Superintendent, is apart-owner of Capillary Concrete AB, org No. 556898-1850.