Trickle Irrigation Conserves Resources

by Gary Mount

Blueberry devotees visiting Terhune Orchards have probably noticed the black plastic pipes decorating the rows between the blueberry bushes. They are there to resolve a watering problem that, until recently, Gary Mount was unaware that he had. Gary’s blueberry experience highlights the importance of a proper irrigation system and the complexities that surround it.

The Immediate Challenge

While there are many acts of nature over which the farmer has no control, water — or lack thereof — is not one of them. At Terhune Orchards, Pam and Gary don’t rely on Mother Nature to provide sufficient water for their plants. Instead, 55 acres of fields and orchards are irrigated using the farmhouse well, the connection to the public water system, and a complex system of trickle irrigation and other methods. The well pumps water at approximately 75 gallons per minute — a small amount as far as farm irrigation goes. But, because Terhune Orchards grows so many different fruits and vegetables, the farm is divided in “zones” that can be turned on or off depending on the moisture needs of each zone. This simple explanation describes a well-tuned system of irrigation that includes machinery, personnel, and resources.

The detective work began during 1999’s El Niño summer when Gary noticed that the blueberries were not growing to his expectations. As do most fruit and vegetable farmers in New Jersey, Gary relies on a complex irrigation system to provide the appropriate amount of water at the right time to make Terhune Orchards’ produce the best it can be.

His first approach to the blueberry problem was to check the trickle irrigation system used to water the bushes. Conventional wisdom suggested that bush roots would be densest near the underground water emitters — the roots sense the water and grow towards it, no matter where it is. However, because of a 5-inch layer of organic mulch positioned above-ground and around the bushes for weed control, the blueberry roots remained in the mulch and never grew downward in search of the water supply. In response, Gary repositioned the pipes on the surface to bring the water supply closer to the roots.

The Long-Term Solution

In an area that often requires its residents to conserve water during the driest parts of the summer, the Mounts are especially interested in and concerned about how to minimize their use of water while maximizing the effect of the water they use.

irrigationDuring the summer months, Pam and Gary hire a teenager who zips around the farm on a golf cart several times a week recording soil moisture readings. What makes this possible is a tensiometer with two attached wires, which are visible above ground. The tensiometer is a tiny device which consists of a porous material that registers electrical resistance according to the moisture content of the soil. When the reading is high, the plants need moisture; when the reading is low, the ground is moist enough.

Two sensors are buried close to each crop to be monitored. One is placed at a depth of between ten and twelve inches and a second at twenty inches. By placing the sensors at different depths, Gary can pinpoint areas of moisture — whether the moisture is on the surface, well below the surface, in both places, or in neither place. He uses the information to adjust the amount of water applied to the crops. If the bottom sensor indicates dry soil, the crops need a good dousing. If the soil near the surface is dry, but the bottom soil is wet, less water is added.

According to Gary, one of the challenges to growing so many varieties of fruits and vegetables is juggling their diverse water and nutrient requirements. For example, too much water for cantaloupes makes them mushy inside and tasteless, too! However, tomatoes and squash thrive on generous amounts of water. To further complicate the equation, fruits and vegetables need different amounts of water during the various stages of their life cycle. For example, those water phobic cantaloupes need more water as seedlings than they do as mature plants. Another factor Gary must consider is that the clay-like soil at Terhune Orchards requires different watering schedules from the sandy soil found in southern New Jersey.

In addition to checking moisture levels, Gary can also check on the plants’ general appearance. The flower cutting gardens, for example, experience a considerable number of visitors walking through the rows cutting flowers. With so many people cutting the flowers, the plants occasionally need a nutritional cocktail. This is easily accomplished with the trickle irrigation system — Gary simply adds nutrients to the water flowing through the trickle irrigation system within the flower beds to feed and water the plants simultaneously.

Although much of the Terhune Orchards fields and orchards are serviced by trickle irrigation, some crops benefit from overhead irrigation. Field crops, such as corn, rely on overhead systems because it is impractical and costly to lay trickle irrigation pipes across so many rows of plants! This type of irrigation requires a large amount of water, so Gary limits his use of overhead or sprinkler irrigation.

One of the unfortunate disadvantages of an overhead irrigation system is the propensity to encourage diseases especially for those plants growing in clay-like soil. Although a trickle irrigation system is more expensive to buy and more complex to install and service than an overhead system, Gary firmly believes the results justify the cost – fruits and vegetables of outstanding quality and flavor. Terhune Orchards’ customers concur!