Natural grass reinforcement

More in this section

• Insights
• The choice of the pitch
• Fields in Natural grass
• Fields in Synthetic Turf
• Experience in the field
• FAQ - Hybrid grass
• Natural vs Synthetic
• Zeolite - mineral soil conditioner
• Cocopeat - organic soil conditioner
• Cork - elastic element
• Irrigation management
• Natural grass reinforcement
• Protection of synthetic turf
• Ground levelling
• Irrigation system
• Drainage system
• Slit-drains in the soil
• Drainage layer
• Growth medium
• Successful installation
• Renovating hybrid grass
• Gypsum calcium saves water

The innovative POWERgrass hybrid grass vs. old generation hybrid grass: defining and comparing limitations and advantages.

The demand for hybrid lawns is constantly increasing, so it is good to provide a clear definition and differentiate hybrid lawns from reinforced natural grass systems.

By analysing the etymology of the words, it is easy to understand that reinforced natural grass is defined as: the combination of methods that use synthetic products (microfibres, elastic fibres, netting mixed into the growing medium, green synthetic fibres implanted into the growing medium and synthetic grass integrated into the growing medium) to reinforce natural grass.

Within this category, therefore, there are also synthetic turfgrass turfs that are infilled with plant growth medium where the natural grass grows in the space between the synthetic fibres. In most cases these turfgrasses include a specially designed backing that, at least from a theoretical point of view, should allow the roots to cross over and grow into the growing medium under the backing. In a nutshell, natural grass grows and thrives within a synthetic turf.

Many people therefore refer to this mixed grass as a "hybrid lawn", but it is worth taking a step further to better understand what this really is. Analysing the etymology of the word hybrid, from an agronomic point of view, this term would be improper because there would have to be a genetic "fusion" and this is impossible.

Natural grass grows among synthetic fibres

Therefore, considering the mutual advantages that these systems offer between natural and synthetic grass, we can say that it is a symbiosis, so it would be fair to give a scientific definition of "symbiotic mixed lawn" or "symbiotic mixed grass".

However, taking a cue from the automotive sector, the term hybrid is conventionally accepted for a car powered by two different energy sources such as petrol and electricity. Drawing a parallel in the field of sports fields, a "hybrid lawn" can be defined as a mixed natural and synthetic grass where one can play alternately with or without natural grass.

This also coincides with market demand and is the concern of many who use the playing field to an extreme. In short, by setting a new market standard we can define the hybrid lawn as a system that provides the right conditions for the growth of natural grass from the start and a playable pitch even in those cases where, for whatever reason (extreme use, weather conditions or human error), the natural grass could possibly be damaged.

POWERgrass hybrid lawn has innovative features and offers better playing and growing conditions than any other reinforced natural grass or old hybrid lawn system and at the same time offers a playable sports field even without natural grass. The synthetic grass is stable and the natural grass can be easily installed with simple seeding.

Reinforcing natural grass is not so simple; it is necessary to respect the laws of nature, i.e. to encourage gas exchange in the plant substrate and to keep its density within 1300 kg/m³.

Hybrid lawns are nothing new! The first system was developed in the USA in 1993. It immediately seemed like a brilliant idea, but had a limited spread for a few reasons, let's examine them:

1. difficulty in attaching the synthetic fibres to the open backing:
   • The roots provide support for the natural grass, absorbing water and fertiliser from the soil, and in order to carry out their function, both they and the bacteria that mineralise the nutrients need to breathe. Since the roots have to breathe and stimulate development in depth, including under the backing, the classic (closed) polypropylene (PP) fabric and latex (SBR) or polyurethane (PU) coating necessary to secure the fibres to the backing in the case of traditional synthetic grass could not be used; in fact, the industry has tried to attach the synthetic grass fibres to a specially designed fabric that is partially biodegradable, which over time should have partially decomposed, forming numerous spaces for the roots to penetrate the substrate and make them grow even below, in the plant substrate; in reality, decomposition does not take place in time, compatible with the requirements of natural grass for rapid establishment, as it depends on numerous technological and environmental factors;
   • In most synthetic turfgrass structures for hybrid systems, the attachment of the synthetic turf fibres is weak and over time the partial degradation of the substrate is likely to further loosen the attachment of the synthetic turf fibres to the substrate, so the natural grass simply remains anchored to the mesh; The synthetic grass fibres do not contribute to the stability and when the natural grass is weak or worn, it gives way and the synthetic grass fibres are removed along with the natural grass sod and the plant substrate, uncovering the fabric, so the work has to be done from scratch;
     Warning! Some companies still offer a hybrid turf fabrication by lightly attaching the synthetic grass fibres to the mesh with a holding value of less than 30 N. The synthetic grass produced in this way is incomplete, so that when the infill material is applied, it is not possible to brush the synthetic grass intensively and so the synthetic grass fibres must necessarily protrude at least 15-20 mm beyond the plant substrate; In fact, we often see the artificial grass fibres buried in the plant substrate and they have no protective function for the natural grass crown and the only plausible reinforcement is for the roots to anchor themselves on the artificial grass mesh;
2. unfavourable natural grass growth conditions:
   • in some cases, during the first growth period, the roots do not penetrate the artificial grass backing until the backing has partially decayed; in the meantime, they grow horizontally over the backing, contributing to the formation of felt; in order to support the growth of the natural grass from a water point of view, we are forced to water frequently and as a result the roots remain 'nice and comfortable' on the surface over the backing: it is well known that a lawn under these conditions cannot withstand the stress of intensive trampling,
   • in some cases, excess moisture associated with rich biological activity consumes oxygen (O₂) in the soil, triggering an anaerobic activity that consumes oxygen from water (H₂O) and sulphur oxides (SO₂ and SO₃), thus releasing hydrogen (H) and elemental sulphur (S); The latter form a very potent acid, a toxic poison, hydrogen sulphide (H₂S), which has the characteristic odour of rotten eggs; the persistence of these conditions causes irreversible intoxication of the natural grass, which turns red, has no roots and dies;
   • Some companies attach the synthetic grass fibres to the backing by spreading a liquid adhesive over the entire surface or by using one of the classic methods for entirely synthetic grass, i.e. the use of latex, polyurethane, or thermoplastic, and have a "high" number of holes to facilitate the passage of roots; in truth, the roots do not pass through, due to the fact that the number of holes is limited and above all because the backing is flat and smooth: the spaces between the holes are impermeable, so the water deposited on top of the backing forms an "invisible water barrier", due to the surface tension of the water which obstructs the gas exchange and consequently the growing conditions for the roots are not favourable under the backing; another plausible explanation is the fact that the water deposited on top of the backing helps to retain an excess of humidity in the rhizosphere above the backing, intensifying the phenomenon of intoxication with the formation of hydrogen sulphide (H₂S).
3. excessively hard court surface:
   • over the years we have always tried to supplement the synthetic grass with a sand vegetal substrate following the USGA regulations; sand is a material that forms a highly porous growing medium about 35% (10% micro-pores and 25% macro-pores), even when compacted it is therefore permeable to water, but after a certain number of hours of play the playing surface becomes hard both for the players but also for the development of the roots and the playing field requires the intervention of Verti-Drain to break up the sand vegetal substrate;
   • mixing or implanting synthetic fibres deep into the sandy plant substrate increases the hardness of the substrate and requires more frequent use of Verti-Drain;
   • in some cases, the application of an open warp and weft fabric forms a very compact surface underneath it and the roots find greater resistance and no longer penetrate the sandy plant substrate and if no action is taken, the playing field also hardens on the surface and the natural lawn tends to thin out;
   • in some cases, the application of an excessively open net favours the penetration of sand into the meshes of the net, partially obstructing the holes and hardening the backing; in fact, the vertical compression caused by players and the transit of maintenance machines contributes to the horizontal tension of the net; the hardening in the area of the backing is perceived excessively on the surface by the player and at the same time the roots of natural grass find excessive mechanical resistance precisely because the net is partially obstructed and hardened.

POWERgrass, product and method: the problem-solving approach.

The search for a solution to the problems previously examined led to a lengthy study to understand in depth the merits and shortcomings of artificial turf and plant substrate.

After a long study and direct experience in the field by the partners involved in the POWERgrass group, we realised that it is essential to develop an indivisible set of characteristics that are essential to create the ideal hybrid grass system:

1. use strong, resilient synthetic fibres to maintain the upright position above the walking surface and truly protect the crown of the natural grass;
2. Welding the synthetic grass fibres well to a breathable substrate without blocking its porosity is also a must in order to clog the synthetic turf with the growing sandy substrate, brushing and harrowing its fibres so that they protrude above the surface 20-30 mm and protect the crown of the natural grass; during subsequent maintenance it is then possible to remove the felt (scarify with springs) or all of the natural grass (re-turfing) without damaging the synthetic fibres;
3. use a backing for the synthetic turf that is non-biodegradable, open, with a three-dimensional structure, and therefore uniformly breathable over the entire surface; in detail, there are further aspects that characterise the synthetic turf backing that are just as essential for providing an ideal system for playing and growing natural grass, such as:
   • the backing must be soft and flexible at each intersection of the holes to allow for better interaction of the player's cleat with the flooring and to avoid hardening of the surface;
   • the substrate must have high porosity due to more than 160. 000 interconnected holes that, thanks to their three-dimensional structure, prevent water stagnation above the surface and allow gas exchange; at the same time, the size and shape of the holes is such as to a) allow the roots to penetrate right from the start of natural grass growth, thus reinforcing the anchorage of the turf sod that drastically increases resistance to tearing caused by sliding players and b) prevent the passage of sand, to keep the internal structure of the substrate open and soft;
   • finally, the substrate must be warp-free due to its knotted fibres at each junction, so it is not possible to unravel its texture following multiple drilling operations required to loosen and aerate the sandy plant substrate beneath the substrate.

All these features form the ideal building block for an excellent, more unique than rare hybrid system, protected by no less than three international patent applications.

Il ZOEsand, the elementary soil improver for the POWERgrass method

An optimal hybrid system also requires a customised plant substrate to optimise the performance of the sport, the growing conditions of the natural grass and the development of the roots above and below the backing.

ZOEsand is the result of extensive research and intuition thanks to a deep understanding of the two worlds of natural and artificial turf.

ZOEsand increases the porosity and retained moisture in the sandy growing medium, provides its insulating properties to reduce extreme temperature variations in the rhizosphere during summer heat and winter frost, gives a cushioning effect in the sports surface, reduces soil compaction and the bulk density of the growing medium.

Finding the right mixture for growing natural grass in a hybrid lawn system was not easy; it took more than 2 years of study and testing of all possible combinations with the mixtures available on the market. Today the results amaze the world's best scientists.

Thanks to this research, a special mixture of sand based on USGA prescriptions has been formulated with a vegetable organic substrate: ZOEsand, a perfect patent to be integrated in hybrid lawns.

ZOEsand contains coconut peat, the finest cork and zeolite sand. Integrating ZOEsand into the growing medium is just as important to improve performance, resistance, durability and drastically reduce maintenance costs.

• coco peat will treat moisture and generate humus in the growing medium to provide carbon for microorganisms over a long period;
• zeolite sand will increase soil fertility by increasing CEC (Cation Exchange Capacity);
• gentle cork is stable over 60% for about 100 years and is used to balance the temperature and air/water content in the growing medium, reduce compaction and provide a softer playing surface;