Irrigation System Selection

Irrigation systems can be used for more than just providing water. They can be used to apply pesticides and fertilizers.  Chemigation (pesticide application) is best achieved with systems that consume smaller quantities of water because this reduces the amount of chemicals needed. Micro-sprinklers may also be used for chemigation.  If foliar application of a chemical is necessary, overhead irrigation is required.  If chemical precipitation is a problem, the stream type directed only to the container substrate allows the foliage to remain clean and free of chemical residues.  Capillary mat systems are not appropriate for chemigation because water application is not applied directly to the container substrate, making the rate of application difficult to achieve.

Other important considerations when designing an efficient, effective irrigation system include the quantity and quality of the water, the pumping and power requirements, and the distribution and control systems.  Generally, an irrigation expert will be needed to develop the appropriate irrigation design and layout.  The source of water must be carefully evaluated to determine if the quality and quantity of the available water are adequate.  An average water application in a nursery is ½ - 1 acre-inch.  One acre-inch of water is 27,154 gallons.  The amount of water effectively utilized to apply 1 acre-inch with a 75 percent efficient system is 36,205 gallons. Thus, the water source must be large enough to supply this much water to the total number of acres under production.

Typical sources of water for nurseries in South Carolina include surface waters such as lakes, rivers, streams, collection ponds, and wells.  Any source of water not constantly recharged by ground or surface waters (e.g., such as a collection pond) must hold substantially more reserve water than is needed for a single irrigation.  Water quality must be evaluated carefully in initial planning.  The pumping rates and power requirements necessary to operate the system must also be determined to ensure an adequate rate of water delivery.  The distribution system selected depends on whether the system is permanent or semi-portable.  In a permanent system, the pump, power source, and the main and lateral pipelines are all set in fixed positions. In a semi-portable system, the lateral lines and application equipment are portable while all other components are fixed. 

The average irrigation event may have 25-75% efficiency (i.e. the amount of water lost may range from 75-25% of the total amount applied). Production of larger crops that require increased spacing can result in even lower irrigation efficiency.  Over the production period of a crop, only 13 – 20% of the water applied is actually retained for plant growth; the remaining amount is lost to evaporation or runoff.  Thus, it is very important to plan for efficient water application and know the volume of water you are applying.  A simple flow meter installed in your irrigation line will enable you to determine volume of flow into particular irrigation zones.  Applying too much water not only wastes any chemicals that have been applied to a particular crop, but there is also potential for crop loss due to disease and root death.

Use all the tools available to either set up an automated system that relies on evapotranspiration, gravity, or soil moisture probes, or monitor irrigation and crop moisture status on a daily basis.  The type of control system needed for an operation depends on the automation and precision desired.  Automated controls can be as simple as time clocks that work with solenoids, or as sophisticated as a computer-controlled system that also monitors and adjusts for changing environmental conditions.  Regardless of the system you choose, be sure it is equipped with rain sensors to turn of automatic irrigation during rain events.  These strategies will help you manage your water resources more efficiently and save you money (reduced water use, reduced fertilizer use, reduced crop loss to water-logged soils, and reduced electrical use - less pumping if water only applied when needed).