Irrigation systems such as flood irrigation apply water at a faster rate in different soils which results in wastage of water through run-off and evaporation. The plants cannot fully utilize all the water since it saturates into the soil quickly. The application of large amounts of water can also result in leaching and water-logging. The rate at which water soaks into the soil depends is determined by the type of the soil. It is therefore important to identify the soil type and how it reacts with water before setting up a drip irrigation system. Since water is a scarce but valuable resource, it should be preserved. Water should be applied at different rates depending on the soil type.
In sandy soils, water moves quickly and goes deep into the soil. The wetting pattern is mainly vertical than horizontal in this soil type. When doing irrigation on sandy soils, higher flow drippers which are spaced closely should be used to ensure that plants receive sufficient water.
Since the soil is dense, the rate of water absorption in clay soil is quite slow. To prevent water from pooling on the surface, drippers should be set to apply water at a slow rate. This ensures that water gets to the roots and minimizes water loss. Water should be applied for longer periods to ensure that the plants receive enough water.
In loamy soils, water gets infiltrated into the soil at a slower rate compared to sandy soils but it gets evenly distributed, horizontally and vertically. Mid-ranger drippers and sprinklers can be a good choice for this type of soil.
Why Soil Testing is Important
Soil testing is important when determining the soil type. Regardless of whether you want to irrigate your nurseries, garden, orchard or your lawn, professional soil testing services will be essential to help you know the rate of irrigation and the drip irrigation kit to use.
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.
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.
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.
For more information about tree fruit irrigation, visit our offices or give us a call.