Irrigation for parks and gardens: systems and components

Saving water and optimizing the management of plant and manpower are the factors behind the evolution of irrigation technologies. Improving the quality and precision of irrigation machines, sprinklers, solenoid valves and other components, along with the automation of systems, acquiring and elaborating data on water, meteorological and physiological governing irrigation are the strong points of the systems built by the manufacturers in the sector.

 

Lawns, flowers, bushes and trees, as for all living beings, need water. Among the functions performed by water are channeling salts dissolved in the lymph of plants; acting as a solvent for mineral substances in the soil, enabling thermal regulation for transpiration and, through photosynthesis, allowing the formation of hydrocarbon compounds to built vegetation tissue. Water accounts for more than 80% of the components essential for a grassy lawn which means great quantities of water are needed. Millions of liters of water are, in fact, taken in annually by lawns which are mowed with regularity.

Irrigation to supply water in periods when there is a lack of rainfall on vegetation is an indispensable practice if the aim is to ensure luxuriant growth in gardens and parks. Through various irrigation methods and systems the quantities of water to offset the shortage of rain for vegetation over the year are supplied. For correct irrigation, account must be taken of the set of interacting climate and weather conditions, the state of plant stress and the state of moisture in the ground.

 

Irrigation systems and methods

The irrigation systems for parks and gardens can be traced back to the operations of sprinkling irrigation methods, micro-irrigation, subsurface groundwater.

Sprinkling irrigation, the most widespread, involves driving water through pipes at high pressure for rain irrigation through nozzles. This simple method is performed with mobile equipment with pipes conveying the water which are moved manually. There are self-propelled units mounted on trolleys and equipped with hydraulic power for moving them independently and the direct transfer of the pipes. For semi-fixed and fixed plants the pipes are partially or fully buried. A pluviometer reports the amount of water dispersed by the irrigation machine per hour expressed in the height of the water per hour (mm/h). To calculate the watering gauge the irrigation machine is equipped with there is the need to know the flow (m³/h), la distance (m), angle of coverage (°) the jet (m).

Microirrigation systems, also known as drip irrigation, comparing distribution, make it possible to achieve considerable savings of water and the financial investment. These systems are used a lot for irrigation on balconies and terraces and becoming more widely used in the open field, especially for flower beds, bushes and trees.

Subirrigation is taking the water directly into the soil, close to the root apparatus, by using pipes made of porous extruded polyethylene. This system, however, is not greatly used.

Saving water, reducing the use of manpower and increasing the efficiency and automation of new machines are the main goals pursued on various fronts. Improving the quality and precision of irrigation machines, drop irrigation machines, solenoid valves and other components along with systems for acquiring and elaborating data on moisture, meteorological and physiological governing irrigation are the strong points of the systems built by the manufacturers in the sector and are the principle features worked on.   

 

Components and accessories

Among the numerous case studies of irrigation plant, many are on components and accessories. Aside from conduits, manometers, filters, couplings, connections, cockpits, collectors, pressure regulators, joints and other accessories, dealt with here are the major components for various types of plant.

 

Irrigation machines

The work of irrigation machines is to distribute water as would rainfall. The equipment can be mounted aboveground or underground. The former provide a solution to adopt for fixed installations in that the latter type creates serious obstacles to maintenance operations, especially to mowing. There are two types of subsurface irrigation machines, static and dynamic. Static systems are normally used for small gardens. They are buried and equipped with aboveground nozzles generally extending above the surface by no more than 3 cm. They are usually equipped with pre-installed heads with fixed or adjustable angles, regulated from 0° a 360°. The filter in the head prevents detrius from clogging the nozzles. According to the angle of work, pressure varies from 1,5 a 2,5 bar and, in relation to the nozzles, the amount of flow comes to 0.5 to 20 liters per minute. Banded rectangular heads are available and especially suitable for strip irrigation of narrow or rectangular lawns. According to the type, the water flow ranges from 2 to 6 liters per minute, whereas for strip irrigation of 1.5 to 3 meters, distance can reach as much as 9 meters.

Dynamic percussion irrigation machinery with metal or plastic hammers are used mostly for big gardens, greenhouses and sports fields. Their water pressure, depending on the type of nozzles, varies from 2 to 4 bar and the maximum jet is from 10 to 25 meters. With nozzles with diameters of 4.5 to 7 mm, the distribution is up to 15 to 60 liters per minute or, with nozzle diameters of 8 to 13 mm, distribution is up to 60 to 200 liters per minute. There is also great variability in performance according to nozzle type for dynamic turbine irrigation machines. As for the percussion types, pressure in operations is from 2 to 4 bar and their distribution is from 4.5 to 9 meters with water flow from 2.5 to 10 liters per minute. Depending on the nozzle type, the range of distribution is from 10 to 15 meters and water consumption from 10 to 35 liters per minute.

Pop-up irrigation systems send the nozzles above the surface of the ground only when in function which means they create no obstacles for mowing the lawn. Some are equipped with nozzle covers which mimic grass to disappear out of sight when withdrawn.

 

Pumps

The work of pumps is to draw water from canals, wells or other sources and send it under pressure to the irrigation machinery for distribution. Pump power depends on the depth from which the water is drawn. Limiting descriptions to those for gardens, electric submersible pumps require power at 0.5 to 1.5 kW for use at depths down to 20 meters below the water level. These pumps are available with or without floats for shutting down the power. Centrifugal electric pumps can be monostage (25-1.2 kW) or multistage (7.5-2 kW). Their maximum depth below the surface of the water for drawing water is 7 meters.

For a golf course the power in play is very high. In general terms, there are 4 or 5 pumps in the pump station for an 18 hole course, each pump with power of around 20 kW.

 

Solenoid valves

These devices control the circulation of water on command. They function at power of 12-24 Volt and are usually equipped with a filter to ensure operation even when the water is not especially clean. Operating pressure is from 1 to 10 bar.

 

Sensors

In recent years sensors have been greatly developed to enable them to detect and transmit the data needed for correctly automating irrigation with the collection of data on weather conditions, temperature, humidity, rain, wind, as well as on vegetation, state of soil moisture, plant lymph flow and the like, and the soil, water levels. 

As regards weather, for example, sensors detecting rain avoid a useless waste of water thanks to the suspension of an irrigation operation in case of rain. In general, they are calibrated to go to work when they detect 5 mm of rain and then, with the evaporation of water from the sensor, automatically return the irrigation program. For vegetation, there are various methods for identifying the time for an irrigation operation. These methods and sensors are targeted on measuring the moisture conditions of the plants, the water potential of the foliage, the temperature of the vegetable cover and the flow of plant lymph.

Thus with autonomous systems there is widespread recourse to striking a water balance in the root zones based on readings of weather and soil conditions provided by sensors in the field. The probes measuring soil humidity are very precise but the drawback is that these calculations of humidity are performed on a matrix which is espacially very variable. This means that a study of the chemical and physical characteristics of the soil is needed to establish the correct locations for detection.

There are various types of sensors for determining soil humidity, those which measure the water potential of the soil based on Watermark sensor type tensiometers. These are basically made of a pair of electroids buried in a special granular matrix which tends to reach equilibrium with the moisture of the surrounding soil. The principle of their function is based on electrical resistance of the soil. There is increasing use of FDR (Frequency Domain Reflectometry) probes which are sensors embedded in the soil for measuring moisture content. The electrical impedance sensor consists of soil probes using electrical impedance measurement. Because of the complex electrical field around the probe, the sensor needs to be calibrated for different soil types.

 

Programming

Programming makes it possible to automate irrigation by setting up the following functions: timing irrigation for a duration of 1 minute to 24 hours and beyond; timing intervals among the various irrigation stations; timing the beginning of an irrigation cycle; the volume of water to use.

These steps can be performed electrically, electronically and via satellite. The most simple system is a battery operated faucet timer used especially for microirrigation on balconies and terraces. For more important plant in the sectors of grounds keeping and agriculture there are solutions based on electromechanics and electronics controlling solenoid valves, electric cables and software for use with satellites for acquiring data and control either by cable or wirelessly, Wi-Fi or radio frequency.

 

Sprinkler booms and drip irrigation

 For drip irrigation, instead of irrigation plant, booms or drip pipes and emitters, drippers, are used. The booms, defined as light, take operating pressure from 0.4 to 1 bar and are used mainly for the irrigation of terraces, balconies and small gardens. On the other hand, pipes used in the open field work with pressures from 0.5 to 3 bar. They are produced in a wide range of spacing between the drippers and water flows in relation to pressure. For balconies and terraces, distribution modules makes it possible to recover water from the main pipe without risk of loss.

Also the drippers along the boom or at the ends are available in various types. Some produce a turbulent flow to prevent clogging by detrius. The self-cleaning models maintain constant flows along the entire boom independent of its slant. These operate are pressures of 0.5 to 3.5 bar and water flow varies from 0.5 to-2 liters/h to 6-10 liters/h, according to the length of the boom and dripper model.  

For drip irrigation systems some type of water filtration is of great importance. The various filter types range from hydrocyclone and vortex separator for eliminating sandy particles to grit filters suitable for dealing with filaments of algae and mucilage and mesh and disc filters for blocking such inorganic materials as lime and fine sand.

 

Computerized management of irrigation

There are many different systems for computerizing and automating irrigation. In summary, it can be stated that the data acquired by moisture and weather sensors, via cable or wirelessly, are transmitted to a Master center which receives them and, in some cases, acts to elaborate them. In some systems, data is elaborated by a server installed for the purpose of providing a water recipe via the Internet. Software then elaborates an algorithm in relation to the data detected by the sensors in the field: the anemometer, temperature sensor, rain sensor, soil moisture sensor, flow sensor and so on. All this for the purpose of identifying the threshold time and generate the command to open the solenoid valves in succession. The software also calculated the volume of water to use beginning with a calculation of the moisture balance.

Some systems deploy a centralized irrigation command which makes it possible to control via a PC, from a single location, programming and the control and monitoring irrigation not only on a single site but on many.