Trickle systems are a good choice for spaced potted plants.
Photos and graphic courtesy of John W. Bartok, Jr.

Making your irrigation system more efficient can save energy, labor and water. The savings will help to pay for the improvements. The following are a few areas that should be considered.

Select the best system for the crop. Overhead sprinkler systems work well on crops that are grown on the floor such as annuals and perennials in flats. They waste a lot of water when used on container crops as up to 75% of the water never gets to the root zone. For these crops, drip, trickle flood and trough systems are a better choice. These save 50% or water and require smaller piping and lower pump pressure.

Design the system for uniformity of application to reduce the total water needed. Over-irrigating some plants so that the driest plants have adequate water is wasteful of both water and energy.

Size the system for the water supply capacity. Compare the peak use against the supply. Use zoning and an irrigation controller to spread the supply over a longer time period. An alternate is to install an intermediate storage tank that will make up the difference.

Size the pipes to reduce friction loss. Water flow is affected by pressure, length and number of fittings. The generally recommended flow rates for 100’ of plastic pipe are shown in Table 1. For longer runs, the flow rate decreases. Most systems have a pressure tank that provides water at between 30 to 50, or 40 to 60, pounds per square inch (psi). Lower pressure reduces flow and higher pressure increases energy use and may damage the plants. Valves and fittings should generally be the same size as the pipe.

Manage the system. Track water use by evapotranspiration rate. There are many sensors that have been developed for measuring the moisture content of the soil. Soil moisture tension is used in conjunction with evapotranspiration estimates to determine how strongly water is held in the soil.

A common system now available to manage irrigation is vapor pressure deficit (VPD). It is a measure of the difference in the humidity inside the leaf and the humidity of the greenhouse air. The computer calculates the amount of moisture lost by the plants and activates the irrigation system to make up this difference.

A zone controller can save considerable water and time as compared to manual control. This frees up the manager for other tasks.

Install a boom system to get very uniform coverage on plants grown in pot to pot, plug trays and flats.

Maintenance can reduce energy use and prevent problems. Select pumps with premium efficiency motors. This can save up to 10% in electricity use. Check voltage at the pump as low voltage will overheat wiring and add to the electricity use. Variable speed drive pump motors have been used but are best for systems with multi zones of different sizes.

Install filters with the correct mesh for the nozzles and check frequently to see if they are clean. Self-cleaning filters can save time and energy. Multiple filters with different mesh may be needed if the water has many particulates.

Check the system frequently for plugged nozzles or drippers. These should be replaced to get even flow to all the plants. Leaks in the pipes also increase water use and should be repaired. A leak of 60 drops per minute will waste 113 gallons per month.

An efficient irrigation system will save water and labor. If properly designed and maintained, it can meet the plant needs without waste.

John is an agricultural engineer, an emeritus extension professor at the University of Connecticut and a regular contributor to Greenhouse Management. He is an author, consultant and certified technical service provider doing greenhouse energy audits for USDA grant programs in New England. jbartok@rcn.com