Lawns defelting and ventilation
Trampling and the passage of the machines on the lawn often give rise to the formation of felt. Maintenance techniques and specific machinery allow the lawn to be efficiently maintained. Defelting and ventilation are the basic interventions for the proper management of the lawn
To ensure that a lawn is kept beautiful and rich it is essential that the soil cultivation layer has a good structure in which water and air can circulate. These conditions over time tend to worsen because of the formation of the felt on the surface and of the compaction of the ground, caused by the trampling and the passage of the machines. When this happens the lawn degrades and the plants lose vigor. To avoid the degradation of the lawn because of inadequate ventilation, the maintenance procedures require a series of more or less energetic interventions, aimed at restoring the starting conditions. These interventions are essentially the operations of defelting and ventilation of the ground.
Defelting
The felt is due to the accumulation on the surface of the soil of organic matter, mainly consisting of leaves, stems or even roots. It is formed because the accumulation rate exceeds the decomposition one. The examination of the composition of the felt shows that it is mainly made of cellulose, hemicellulose, and lignin in different proportions depending on the grown species. The small waste of cut and removed fresh grass decompose very quickly because of the high moisture content and of the absence of lignin, so the high frequency of the cut has little influence on the formation of the felt. This situation also applies to mulching. The matter is different when cutting tall and not fresh grass.
Felt behaves like a straw bed supporting vegetation. However, when it exceeds the thickness of 10 mm, it reduces the normal circulation in the soil of water and air, thus compromising the vegetation growth conditions.
With the defelting process, a part of the felt is removed in order to superficially ventilate the ground to maintain a good microbial activity, accelerate the decomposition of the undecomposed organic substance and improve the water circulation, improving its penetration into the ground and avoiding waterlogging.
In some cases, it may be enough to perform the operation with a metal broom, with a rake or, more effectively, with a toothed harrow. After the process with a harrow, a second passage is necessary with a brush-harvester of the removed felt over the surface.
For a stronger action, it is necessary to use specific machines, also called verticut. The working part of these machines, contained within a protective casing, consists of a horizontal axis rotating at a speed of about 1000 rpm, on which the defoliating blades are mounted. The blades are placed at intervals of 30-50 mm and, by rotating, they make vertical cuts that eliminate the felt on the surface at a depth of 5 to 10 mm. It is possible to choose the most suitable type of scraper knife according to the quality of the lawn on which the intervention is to be carried out. In particular, the thickness of the knife ranges from 1-2 mm, if working on a green or in any case on a high-quality carpet, from 3-4 mm, if the operation is carried out on a rustic carpet.
The smallest, self-propelled and with the driver on the ground machines, have a working width of 40-50 cm and are driven by an internal combustion engine with a power of 3-4 kW. When the removed felt collection basket is missing, a second passage is necessary with a brushing-harvesting machine.
Larger machines are towed or carried, and have working width from 120 cm to 250 cm, even if there are models that reach working widths of 400-500 cm. In these models, the absence of the harvesting basket is the rule.
The frequency with which the defelting operation is carried out depends on the type of soil and the vegetative activity of the lawn. Generally, two interventions per year are required: one in spring and the other in autumn. Before performing the defelting, it is necessary to cut the lawn. The spring intervention can be followed by an overseeding, while after the autumn intervention it is good to fertilize the lawn.
Soil aeration
The aeration of the soil is necessary when its structure becomes excessively compact. The purpose is precisely to reduce its compactness, improving its surface structure, in order to promote drainage and decomposition of organic matter, stimulate microbial life and improve the assimilation of fertilizers.
Depending on the soil conditions, aeration can be carried out by performing scarifying operations, or by drilling or coring. Under certain conditions, a so-called decompaction operation can be carried out.
Scarification. It consists of making vertical cuts in felt and soil at depths between 50 and 200 mm. The working part is a rotor with a horizontal axis on which disks are flanged (70-100 mm in diameter), which carry a series of blades or knives of triangular or spear shape (5-10 per disk). The latter has a length of 15-20 cm.
The smaller self-propelled models with the driver on the ground have a working width of 40-50 cm. Generally, they are driven by an endothermic engine with a power of 3-5 kW. Larger models are carried or hauled with a working width of between 120 and 250 cm. The power of the tractor to which these machines are coupled ranges from 15 kW to 30 kW. As for the defelting machines, there are also models with greater width, up to 500-600 cm.
Drilling and coring. This operation consists in creating artificial air inlets up to a depth of 100-250 mm. The organ that performs the hole is called a hollow cutter. The effectiveness of an aerator is estimated from the number of holes in m2. The hollow cutters have a cylindrical shape and can be full (drilling) or hollow (coring). In the first case holes are made without making the ground less compact; in the second the soil is extracted from the hole (carrot) creating the less compact effect. In this second case, carrots must be removed. Also, this operation is performed mechanically, with specific machines, or by setting the collection device on the aerator machine, so as to avoid a second passage. According to the way the hollow cutter is made to penetrate into the ground, the working device can operate with a rotating or with a vertical action.
Machines with rotary tools use 40 to 100 holes per m2 for a depth that can reach 150-200 mm. They can be self-propelled, carried or towed by the tractor and the working width is 50-300 cm. They are strong machines whose use is aimed at lawns with not very compact soil. Many of these aerators, replacing the hollow cutters with knives, become defelting machines.
The vertical action aerators drill holes perpendicular to the surface without deforming the lawn. They are more effective than those with a rotating action and the density of the holes can even be higher than 1000 per m2, so as to affect more than 25% of the ground, reaching depth even higher than 200 mm.
They can be autonomous, self-propelled, towed or carried-out machines.
The former, with a maximum working width of 150 cm (7-12 kW of power), for contained surfaces; the latter for large surfaces, with a working width of more than 300 cm.
Decompaction operations. A strong use of the lawn, with resulting high trampling, and/or the too frequent passage of machines, can be responsible for excessive compaction of the ground and require incisive interventions, without having to interfere too much with the fruition itself.
The intervention can be performed with two types of machines: bladed decompaction, with which we make some micro-extensions after which the use can take place within 2 or at most 6 weeks; compressed air decompression, following which the use is immediate.
Sandblasting or top dressing
Sandblasting involves distributing a thin, even layer of sand or a mixture of sand and peat on the surface of the lawn. The operation has the function of filling gaps and punctures caused by previous interventions, also reducing any irregularities in the ground, to prevent the formation of felt, and improve the ability of the water to infiltrate the surface. The amount to be distributed depends on the purpose and the lawn. It ranges from 4 to 5 liters per m2 after intense coring, to 0.5 liters per m2 in greens.
Sand must have a reduced particle size with less than 20% of elements with a diameter greater than 2 mm. The operation must be carried out before a scarifying or decompaction operation and after that of coring.
The machines used are essentially sand-blasting carriages, consisting of a hopper with a movable bottom and a brush reel which provides for distribution or are made up of a centrifugal-type sand spreader.
To promote penetration, a rolling must be performed, alternatively, machines have been made, called verti-brush, whose working organs are rotating brushes on a vertical axis which, in addition to uniformly spreading the material, favor its penetration into the lawn.
