Source: Technical IgK Dpt. 9 June 2015

Irrigating with rigor (I)

The adequate irrigation of the turfgrass is the greenkeeper's hardest and most important daily agronomic decision.

Valderrama weather station
Valderrama weather station

Water makes up 80% to 85% of a plant's weight. In most places irrigating, supplementing water, is needed to maintain the quality of the field throughout the year. Good irrigation practices are essential for providing the best playing conditions in terms of surface firmness, speed and uniformity, and turfgrass density.

The irrigation system must be efficient and precise, and so it must be designed and installed correctly, used professionally, and meticulously programmed. It is complicated and requires an expensive investment. Irrigation system project must know three key areas: water sources and storage capacity, water quality, and water balance for our turfgrass species. From here, we can start thinking about irrigating with rigor during maintenance.

Practically every course in the world irrigates with sprinklers. There is a wide variety of designs. Courses can be found with 600 sprinklers, 1,600 sprinklers, and the most sophisticated systems can have up to 4,000 sprinklers. The system requires pressure as the water normally circulates through polyethylene or PVC tubes, and is distributed through sprinklers place on the ground, emitting more or less pulverized as drops with a rain effect.

Many of these systems are completely automatic and controlled with a computer program. The software makes it possible to apply different amounts of irrigation to each area of the course by controlling the activation of each valve and the amount of irrigating time.

The most frequent arrangement for deploying sprinklers is triangularization, with an arc of water that goes from sprinkler to sprinkler to guarantee good coverage in every area of the course. The flow and distance covered by the arc of each sprinkler can also be adjusted by changing the nozzles.

Everything is directed towards an efficient use of water. About of weather station or soil moisture sensors should be used as the main source of information to assist in irrigation scheduling: The right answer to use both methods because they are complementary.

A correct daily calculation of the irrigation needs is possible by measuring the evapotranspiration (ET) expressed in millimeters by unit of time (mm/day = 1/m2 and day), which indicates the volume of water the soil profile loses. This estimate is vitally important for programming the irrigation. The factors affecting the ET include temperature, daytime length (hours of solar radiation), relative humidity, wind and availability of water in the soil. Thus the ET has variable, local character and is a magnitude that is hard to measure.

Many methods, procedures and equations have been developed to calculate evapotranspiration based on the water balance and climate. Nowadays, the most frequently used method for estimating the ET of a plant surface is based on the Penman equation, subsequently modified by Monteith (Penman-Monteith). This equation is based on the measurement of solar radiation, temperature, relative humidity, wind, the type of plant surface, and uses the variable crop coefficients of each species. This requires weather stations directly linked to the computer system.

Knowing direct humidity in the root zone through moisture sensors is the other key reference of measurement of the soil water content, together with other parameters related to salinity and temperature.

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