Tuesday, February 21, 2012

Blueberry Irrigation Methods

On most sites, irrigation is essential for survival of newly planted bushes, and for consistent growth and yield throughout the life of the planting. The types of irrigation  most often used on blueberry  in North Carolina are:

1.  Overhead -- impact sprinklers on 6 ft risers (12 sprinklers per acre) are used for both drought relief and for frost/freeze protection in the spring.  These systems use about 68 gallons per minute per acre (4080 gallons per hour on a 60 x 60 ft spacing) and usually exceed the continuous capacity of available wells,  so water is first pumped into a reservoir (pond), and the irrigation system pumps from the pond.  This is the most common system used on large farms in the coastal plain, where a single pond/pump setup may cover 20-25 acres.

Overhead irrigation can be used for drought relief or for freeze protection

2.  Micro-sprinklers -- Not very commonly used, these are small spray heads on stakes about 12 inches above the ground that wet a 3-ft to 5-ft circle around each bush.  Coverage is better than with drip lines, but like drip, micros cannot be used for frost/freeze protection.  Some growers who have tried micro-sprinklers have since replaced them with drip sytems, because micro-sprinklers are easily damaged by equipment or by farm workers stepping on them during harvest.

3.  Drip line (built-in emitters) -- a heavy flexible line with built-in, pressure-compensated emitters every 18 inches.  Output is usually about 0.5 gph per emitter, or 24 gallons per minute per acre (1452 gallons per hour per acre).  Different emitter spacings are available, and double lines can be used to increase the wetted area.  Water quality has to be good or the tiny emitters will become clogged with sand/grit or precipitated iron and carbonates.  Drip irrigation is the most commonly used system in the piedmont of NC.

Drip line with built-in emitters every 18 inches

4.  Drip line (punch-in emitters).  Similar to above, except the emitters are not built into the drip line.  Emitters must be inserted by hand using a special tool to punch holes in the drip line.  This system can be customized by only putting emitters at the plant, or by adding more emitters at a later date.

Drip line with punch-in emitters placed at every plant

5.  Lay-flat drip tape -- lightweight drip tapes are not recommended..  Most lay-flat tapes are less durable and can only be expected to last one or two seasons.  Occasionally used for temporary systems,  prior to installation of the permanent drip or overhead system.

Other methods of getting water to blueberries have included flood irrigation, water table management (by holding water in ditches around the field), and (in western NC) piping or channeling water by gravity from a spring or well further uphill.