Tree fruit growers may use two types of irrigation systems: solid set sprinklers and drip. Both irrigation systems have their own advantages and disadvantages for a given application. Once a particular type of irrigation system is chosen, an irrigation equipment dealer or a qualified agricultural officer can help you customize it for the particular orchard block and fruit crop.
Solid Set Sprinklers
With this system, laterals are buried in the tree rows with a riser and impact sprinkler exposed above ground. These systems are full coverage systems that apply water to the entire tree and orchard floor. The initial investment cost of this system is high because of the cost of trenching and placement of the PVC laterals and sprinkler heads. Annual operating costs are high because of pumping costs.
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Drip irrigation uses polyethylene laterals with emitters to deliver water directly to individual trees. In practice, only about 40-50% of the orchard floor will be wetted. With drip irrigation the PVC submain and main water supply are usually buried to facilitate machinery operations. These systems are easily adapted to chemigation and because they do not wet the entire tree, they facilitate conventional pesticide applications.
Once you have acquired an irrigation system, you must decide when to irrigate, how much water to apply, and how you will use and maintain the equipment. Irrigation systems must be designed to ensure that both the water supply and the irrigation system can meet peak demand.
Plant root depth, canopy development, growth habits, and nutrient requirements in a given climate largely determine the irrigation schedule. Soil-infiltration characteristics determine maximum water application rates. Actual water use will vary daily throughout the season, so growers must develop a method for ensuring that the crop has a sufficient amount of water available.
Several methods are used to determine when to irrigate, and some of these methods are more reliable than others. By the time plants show signs of water deficiency, such as wilting, plants have been stressed and their growth slowed. Irrigation at this point may save the crop, but production already has been limited.
The appearance of the soil after being squeezed by hand can be used to estimate water content. A common mistake is to feel the soil on the surface rather than around the root tips, where most moisture is taken up. You can avoid this problem by using a soil probe to sample soil in the crop root zone.
Plant water demand also can be estimated daily (based on crop development and climate conditions) and then compared to the soil’s water-holding capacity. Irrigation should begin when the stored soil moisture approaches 50 percent of the available capacity or the plants will become stressed. Moisture content should be measured periodically to verify water use and moisture depletion estimates. With experience, this water budget method can be quite reliable and can be used to predict when irrigation should begin.
The irrigation schedule can account for average weekly precipitation and can help you plan irrigation to apply the difference. However, rainfall amounts are unpredictable, so this method can lead to deficits or excesses that can limit crop performance. For small-fruit crops, growers may wish to raise the water demand to 2 inches per week during fruit development, especially on well-drained soils.
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Equipment Use and Maintenance
Appropriate use and maintenance of irrigation equipment, both during the irrigation season and while in storage, will increase its life span and reduce operating and maintenance costs. Irrigation equipment dealers can provide you with guidelines for operating and caring for your equipment.
The pumping unit and control head will require the most maintenance in terms of lubrication, cleaning, and protection from dirt, moisture, freezing, and animals. Leaking pump seals and pipe gaskets should be replaced when necessary. Sprinkler nozzles that have worn more than 1⁄16 inch larger than specified or emitters that are clogged should be replaced. Mains and laterals, particularly in trickle systems, should be flushed periodically to remove buildup of precipitates and sediment. Equipment used in freezing weather must be properly lubricated and should be self-draining. Careful use and continued maintenance of irrigation equipment will help ensure many years of trouble-free performance.
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