Natural grass football pitches: maintenance and machinery

Grass cover is subjected to deterioration caused by compaction by the feet of the players and insufficient natural light shut out by the height of the stadium stands as well as by thermal stress and a shortage of nutrition. There is a wide range of machinery and equipment for the optimum management of football pitches, for mowing and irrigation, defelting, sand top dressing, re-turfing and fertilization and plant treatment

Grass pitches for professional football, especially for premier division play, are built mainly with natural grass and the construction is usually done with a technique for transplanting turf. A good grass cover must meet determined requirements having to do with the conduct of the ball in rolling or bouncing as well as maintenance in the direction of the impression by kicking the ball on the surface of the grass.

Even after the finest construction, over time the grass cover will deteriorate for many reasons. First there is compaction of the terrain resulting in a reduction in the penetration of the air and water to limit the development of the vegetation. The feet of the players on the pitch are the main cause. Sound use of the pitch in favorable weather conditions should not exceed 6-8 hours of play in the autumn-winter period and 16-18 hours in the spring-summer period. In unfavorable conditions play should be more or less halved. The commitments of football clubs in the championship season and cup play often makes it difficult to respect these limits. Among the other factors which condition the quality of the grass cover are: insufficient natural light often due to stands built too high to increase the capacity of the stadium, a shortage of nutrition, thermal stress and possible fungus attacks.

The maintenance intervals involve: mowing the grass and irrigation, defelting and aerating the soil; sand top dressing and overseeding or complete or partial re-turfing; fertilization, treatment and cleaning.

 

Mowing and irrigation

The ideal height for cutting the grass of a football pitch is between 25 to 30 mm. In the winter good practice is to mow at the height of 30 mm or close to it whereas in the spring-summer period it would be better to reduce the cutting height by 10% compared to the winter height. The mower, generally a ride on type, can have helicoidal blades, 8 or 10 of them, or a horizontal blade. Also robot mowers with work widths of 60-80 cm or beyond are suitable. The frequency of mowing is linked to the development of the grass so that in the summer cutting is done 2-3 times per week whereas in the winter mowing is reduced to once a week. On average over the year mowing is performed 40-50 times. Irrigation is practically indispensable. In the summer watering is needed 1-2 times a week. Irrigation can be done with mobile equipment but pitches usually have an automatic pop-up irrigation system. 

 

Defelting and soil aeration

The formation of felt is due to the deposit of biomass vegetation in less time than it takes for this to deteriorate. When the felt layer becomes excessive conditions are created which reduce or block the penetration of air and water. Self-propelled, mounted or trailed defelting machines are equipped with horizontal rotors fitted with knives in various shapes which, when rotating, make vertical cuts in the soil down to 20-30 cm and lift out the felt.

Soil compaction reduces water permeability which, when conditions are right, should exceed 100 mm per hour. Perforation or coring the soil can be done to combat compaction. The former operation is performed by tines mounted on a rotating axle or a goose neck axle; for the latter, hollow tines extract soil cores. During the playing season there is the tendency to core the pitch at not too great a depth whereas when the pitch is at rest coring can be done to greater depths to create vertical drainage. The density of the holes left varies from 100-150/m² and can exceed 500 holes/m². Hydraulic aerators make this operation less invasive with machinery which cores the soil with high-pressure jets of water. In normal conditions, these aeration and coring operations are performed twice a year. 

 

Sanding, overseeding and re-turfing

After aeration or coring verti-draining operations comes sand top dressing which not only fills the holes but is also done to reduce irregularities in the terrain and the formation of felt. The operations consists of spreading sand of a determined granulometric composition. Distribution is performed by a machine which gravity spreads the sand or uses centrifugal force. A verti-brush is used to help the sand to penetrate the soil with round brushes which also improve the smoothness and uniformity of distribution. The quantity of sand used ranges from 3.5-4.5 liters/m²  following coring at 0.5 litrer/m²  in other cases. There can be recourse to overseeding when the grass cover has lost density of less than 100 regrowth/m²  or, as is the case for some stadiums in South-Central Italy, overseeding is done in the autumn with a mix of microthermal species for a microthermal cover. The cover, in fact, turns yellow when the cold arrives so overseeding microthermals have the function of keeping the cover green. Another type of maintenance operation on the cover is the partial or total replacement of the grass turf in damaged areas of the pitch or the on entire surface area. The tendency in important stadiums is to keep available an area with the same characteristics and the same species as those on the playing field from which sod can be lifted for patching in a quick and easy operation with little impact. 

 

Fertilizer, treatment and cleaning

Aside from the nature of the terrain, fertilization is linked to the intensity of use. For the pitches in the top division the quantity of nitrogen based fertilizer reaches 400 units annually whereas phosphorus and potassium quantities come to between 100 and 200 units. These operations come along generally 4-6 times per year; recourse to slow-release fertilizer makes it possible to reduce this number of operations. There are treatments to apply only to counter a fungus attack which is prevented mainly by good maintenance practices. Cleaning is substantially clearing the pitch of extraneous materials whereas the stands must be cleared of everything the fans leave behind using backpack blowers.

 

The costs

Sound maintenance carries costs which cannot be neglected. These costs in general can come to € 50,000 or up to € 150,000 annually. The expense incurred for totally re-turfing the pitch can reach around € 200,000 to € 400,000 for each transplant.