Turfgrass beds, sod transplanting as an alternative to seeding
Turfgrass beds are an alternative to sowing, especially for sports turf and ornamental turf. The origin is ancient, as the pioneers of this technique were the Arabs, Greeks and Romans. Subsequent developments have taken place slowly over the years
In the 17th century, transplanting was mentioned in Great Britain in the gardening book written by J. Rea and J. Evelyn: sod was taken from natural pastures with a thickness of 120-150 mm. In 1890 W.J. Beal, a researcher at the qualified experimental station in Michigan, produced the first scientific publication on sod transplantation. However, it was not until 1917 that Piper and Walkey, in their book on golf turf, provided the first complete technical description of turf transplanting. Also in the USA, in the early 1900s, the production of turf in a specialised way in the nursery began, while it was not until the 1940s that the first machine for removing turf from the nursery was introduced, and the 1960s that the turf was rolled up. In Europe, the sod transplanting technique became popular in 1960, especially in Great Britain, France, Germany and the Netherlands, and was subsequently applied and spread in Italy. Compared to sowing, sod transplanting offers these substantial advantages: complete and immediate coverage, reduced time for use, possibility of installation throughout the year. On the other hand, the cost of installation is much higher than for sowing. The phases involved in the sod transplanting technique can be summarised as follows: growing in nurseries, sod removal and transport, sod planting.
Growing in nurseries
Cultivation is done according to two techniques: open field and above ground. The first is definitely the most common and is the subject of this article. For cultivation in the open field, sandy and sandy-loamy soils are preferred, as they promote drainage and growth and make it easier and more effective to remove the sods. The production of this turf requires great professionalism, with specific cultivation and maintenance schedules. The soil is prepared with a cultivation substrate generally made of silica sand and made perfectly level. Sowing is done with lawn seeders with different mixtures depending on the function and use of the turf. Unlike in the past, the market now offers a wide range of choices to meet the most diverse needs in the field of quality turf, including the production of turf for specific functions to meet particular soil and terrain conditions.
Cultivation in the field - before the turf is ready it takes at least 12 months - but generally lasts for 18 months. Maintenance care during this period must be particularly careful, with daily monitoring, in order to meet the needs of irrigation, mowing (very frequent), as well as to carry out fertilisation and defence against weeds and parasite attacks. All this requires the use of skilled labour and appropriate machinery and equipment to carry out maintenance work effectively without compacting the sod and to remove the sods of turf.
Cultivation above ground is done in special containers, with a substrate generally made up mostly of finely ground and calibrated pine bark and appropriately treated wood sawdust, so as to form a draining structure favourable to root development. The resulting substrate is placed in a thin layer on polyethylene film and the seed mixture is distributed at the same time. The formation of the turf ready for transplanting takes only 6 months. A special case involves the production of clumps of ground cover, i.e. clumps with perennial herbaceous plants that propagate by rhizomes and stolons, suitable for covering heavily shaded areas instead of turf.
Harvesting and transport of the sod
The transplant turf is generally marketed in slabs of about 1 m2 and even smaller areas and, more frequently, in rolls. The small rolls are 40 cm wide and up to 2.5 m long. They can also be handled and laid manually. Large rolls are 0.50 to over 1 metre wide and over 10 metres long (up to 30-50 metres). Harvesting, transport and planting is fully mechanised.
Harvesting machines are self-propelled and can be with a driver on the ground or with a driver on board. The former are a kind of walking tractor with front wheels and, at the rear, a cutting blade that penetrates the ground to a depth of a few millimetres. They produce small slabs or rolls. Self-propelled machines with a driver on board are powered by a diesel engine. The working unit consists of a cutting apparatus that penetrates the soil, cutting and removing the top layer, and a conveyor belt that unloads it. They can produce both slabs and rolls. The depth of penetration is adjustable from a few mm to 50 mm. Big rolls are usually mechanically wrapped in plastic film or netting to protect their integrity. It is important to check the quality of the sods, both by visual inspection of their appearance and by measurements of their mechanical strength (horizontal force required to break up the sod).
Big rolls are transported by lorries, which can be uncovered, tarpaulin-covered or refrigerated. The use of the latter is linked to the time elapsing between harvesting and planting the sods, which must not exceed 36-48 hours. When this time is exceeded, the rolls must be stored in refrigerated rooms in order not to compromise the result.
Planting the sods
The soil receiving the sods must be well drained and well prepared as required for sowing. In addition to drainage it is therefore important to carry out good fertilisation with the possible use of soil improvers (the soil improver should be well mixed into the substrate to a depth of 100 mm). The surface must then be worked (150 mm deep) and levelled, which can be done with a laser levelling blade, in order to obtain a perfectly flat surface. In recent years there has been an increasing tendency to use mycorrhized consortia (a combination of fungi and bacteria) to improve both soil fertility and plant resistance to disease. This is because a natural interaction is created in the rhizosphere between plant and microorganisms, with mutual exchanges from which the plant benefits.
The rolls are placed in the ground using unrolling machines. The unrolling device can be positioned either at the rear or at the front of the tractor machine. Slabs can also be planted mechanically; special robotic machines have also been developed for this purpose.
Once the lawn has been laid, it should be rolled to ensure perfect adhesion of the roll to the substrate and rapid rooting in the substrate. During the first week, the lawn should be watered frequently, and from the second week onwards the watering should be reduced. On the whole, the irrigation requirement of the rolled lawn at installation is less than that of the lawn at sowing. For each irrigation, the water supply is approximately 15 litres/m2 (approx. 150 m3 per hectare). Depending on the type of mixture, the first mowing is done 6 to 10 days after planting.
