Orchard Irrigation
Proper irrigation is essential to maintaining a healthy and productive orchard. Over-irrigation slows root growth, increases iron chlorosis in alkaline soils, and leaches nitrogen, sulfur, and boron out of the root zone, leading to nutrient deficiencies. Over-irrigation can also induce excessive vegetative vigor, and reduce fruit size.
Excessive soil moisture also provides an environment ideal for crown and collar rots. Applying insufficient irrigation water results in drought stress and reduced fruit size and quality.
Properly managing irrigation is analogous to managing money. In addition to knowing your current bank balance (soil water content), it is important to track both expenses (evapotranspiration) and income (rainfall and irrigation).
Irrigation System Design
Irrigation system design should take into account water availability and quality, orchard slope, size and soil texture, as well as tree and rootstock selection to maximize yield, fruit quality, tree health, and water conservation. While flood and over-head irrigation may still be used in some Intermountain West orchards, these systems are less efficient, can spread diseases and often lead to overwatering. Micro and drip irrigation systems are preferred for their efficiency and versatility. With careful design they can be used in a variety of orchards. Important considerations when designing a system include filtration systems to prevent clogging, size of tubing and emitters, pressure regulation and distribution uniformity. See CSU's bulletin for more specific information on designing an irrigation system for your orchard.
Irrigation Scheduling
Properly managing irrigation is analogous to managing money. In addition to knowing your current bank balance (soil water content), it is important to track both expenses (evapotranspiration) and income (rainfall and irrigation). The focus of this section will be on using evapotranspiration, the amount of water used under various climate conditions at different crop growth stages, to schedule irrigation. Evapotranspiration is an important concept to understand and when properly applied provides the most accurate method of irrigating for tree needs. Several online tools and apps are available to help calculate evapotranspiration based on weather. In addition, soil moisture sensors can help growers monitor soil moisture. Other less accurate methods, such as only monitoring soil moisture by feel or using a set amount of water based on average estimated water use for a crop across the whole season, can be useful but typically result in over-irrigation or in some cases under-irrigation depending on climate, growth stage and the skills of the grower. If the later method is used, growers should adjust scheduling based on in season precipitation and fluctuating temperatures to account for changes in evapotranspiration when possible.