Dripping with profits

Drip irrigation is an irrigation method that allows water to drip slowly near the plant roots through a network of valves, pipes, tubing and emitters, sending precisely controlled applications of water and fertilizer into the plant. When properly designed, maintained and operated, a drip irrigation system can be a production asset for a vegetable farm, no matter its size. However, using drip irrigation for profitable vegetable production requires an understanding of several basic engineering and horticultural concepts and their application.
 

A history of innovation

Early forms of drip irrigation can be traced back to ancient times where clay pots were filled with water and buried in the ground, which allowed the water to gradually leak into the root zone of nearby vegetation. A researcher at Colorado State University, E.B. House, began applying subsurface water directly to the root zone in 1913, while perforated pipe was first used for irrigation in Germany around 1920. After World War II, the ability to mold plastics became widespread and more cost effective, paving the road for innovations in the manufacturing of drip irrigation system components. At this time, Polyethylene (PE) tubing, also referred to as “micro tubing” or “spaghetti tubing”, and early versions of emitters (drippers), became more commonplace and were installed throughout the U.S. and Europe.

In Israel, Simcha Blass and Yeshayahu Blass were innovators in the area of emitter design. They created a method that allowed water to flow through longer and wider passageways inside of the emitter. These “labyrinths,” as they were called, resulted in less clogging.The velocity of water moving through the labyrinth helped to slow it down creating a “drip.” In 1959, Kibbutz Harzerim partnered with Blass to form a company called Netafim, which further developed and tested this concept. Netafim patented the first drip irrigation emitter and helped the technology of drip irrigation to rapidly expand through Australia, North America and South America in the late ’60s.
 

All the different parts

There are two kinds of drip irrigation systems. In a permanent drip irrigation system, the order of equipment is: backflow prevention device, control valve, filter then pressure regulator. In add-on drip systems, where a head assembly is attached to an outside faucet or hose, a faucet valve may precede the backflow device. In the case of an add-on drip system, the valve is opened with a manual turn of a faucet handle or with a mechanical or battery-operated timer attached to the faucet. The head assembly in this case would consist of a manifold of backflow preventer, filter and pressure regulator.

The drip irrigation system delivers water to each plant through a thin polyethylene tape with regularly spaced small holes called emitters. Selection of drip tape should be based on emitter spacing and flow rate. Typical emitter spacing for vegetables is 12 inches. However, 4- to 8-inch emitter spacing is acceptable depending on the crop. The drip tape flow rates can be classified into low (<20 gallon/100 feet per hour), medium (20 to 30 gallon/100 feet per hour) and high (>30 gallon/100 feet per hour). Clogging of the emitter increases as the flow rates decrease. In the field, drip tape should be installed with the emitter upward to prevent clogging from sediment deposits settling in the emitters between irrigation cycles.

A backflow prevention device is critical to prevent contamination with fertilizers to household potable water. Small anti-siphon devices are available that screw onto a hose bib for add-on systems. Contact your government building department or water provider to find out what backflow prevention is required locally. A 150- to 200-mesh filter can be used for relatively clean municipal water. Filters with a higher mesh count have a greater screening capacity. Y or T filters are convenient because they don’t require dismantling connections for cleaning, as do in-line filters.

A pressure regulator is essential for maintaining pressure that meets product manufacturer specifications. These regulate the water pressure at a given water flow, thereby helping to protect system components. Most drip irrigation systems operate at water pressures ranging round 40 pounds per square inch (psi) depending on the size of the system. Take into account the pressure that will be needed for elevation changes. For example, add 5 psi to the operating pressure for every 10-foot rise in elevation above the point of connection to the water source. Pressure compensating emitters minimize low head drainage.
 

Goal

The ultimate goal of a drip irrigation system is to bring water to the crop. The main parameters determining crop water use are: type of crop and row spacing. Drip irrigation systems should be able to supply 110 to 120 percent of crop water needs. In designing a drip system keep in mind that vegetable crops need approximately 1.5 acre-inches of water for each week of growth or approximately 20 acre-inches of water per crop. Actual water use will approximately be more than this depending on weather and irrigation efficiency.

Benefits

Drip irrigation brings the water to the plant root zone and it requires half to a quarter of the volume of water required by comparable overhead-irrigation systems. It can improve the efficiency of both water and fertilizer because of joint management. Precise application of nutrients to the plant root zone reduces nutrient losses and fertilizer cost. Nutrient applications may be better timed to meet needs. Concentrating irrigation to specific areas around plants helps in reducing weeds from germinating nearby because they do not have the moisture necessary for seedling growth. Retaining the moisture at the soil level reduces water loss to wind and evaporation, especially when combined with raised beds covered with polyethylene mulch. Furthermore, drip irrigation systems may be programmed with an irrigation controller that’s simple to manage.
 

Points to consider

A permanent drip irrigation system requires an economic investment that can cost hundreds of dollars or more. Growers new to drip irrigation should start with a relatively simple system on a small acreage. Drip irrigation requires maintenance and high-quality water and soluble fertilizers. Using high-quality parts prevents constant maintenance and high-quality water and fertilizer prevent clogging. Improper drip irrigation installation (spacing) often culminates into poor root development and dieback. For example, looping your tubing too wide or installing a small quantity of water emitters creates drought conditions and may resort to shallow growth to find moisture and die back. Although irrigation filters stop debris from clogging tubes your system still needs a periodic flushing to remove mineral buildup. In fact, you need to check each emitter for any blockages so that the water pressure does not build up within the tubing and damage your entire system. Additionally, stake your tubing down to prevent accidental falls. Drip-tape disposal causes extra cleanup costs after harvest.

T. Casey Barickman is an assistant research and extension professor in Horticulture at Mississippi State University. His research is in small fruit and vegetable production with an emphasis in plant physiology and nutrition. He focuses on evaluating sustainable and organic production systems, greenhouse vegetable production, nutrient management, environmental stress physiology, and plant growth regulation. He can be reached by email at cb2407@msstate.edu or by phone at (662) 566-8001.