Avocado Grove Salinity Management Best Practices

The salinity of avocado grove soil is influenced by several factors. Frequent use of salty irrigation water will influence the salinity of the soil. Avocado grove salinity is also influenced by rainfall content and timing, soil drainage, and irrigation practices. Usually, rainfall contains low amounts of salts and can dilute salts present in the soil of the avocado grove. If the rainfall is of sufficient volume or duration, and the soil has internal drainage, the added rainfall is enough to leach salts from the soil. During dry conditions, water evaporates and salt in the soil becomes more concentrated.

EC measurement of the irrigation water source is an excellent avocado cultural management tool.

A few key facts to remember about avocado grove soil salinity:

• The top six inches of avocado grove soil are the most important to manage for salinity because avocado trees have a shallow root system.
• In general, soil-water salinity is higher than irrigation-water salinity.
• Salt builds up in avocado groves when avocado trees are irrigated with salty water and the soil has not been properly leached.

Salinity management in avocado groves involves irrigation and soil-leaching cultural management practices. Best practices include:  

• Monitor salt levels and leaching
• Plant salt-tolerant avocado tree rootstocks
• Use low-salinity irrigation water
• Practice avocado grove soil leaching (a small amount of excess irrigation to remove salts from soil)
• Use proper irrigation equipment and good irrigation management
• Apply gypsum

Avocado irrigation facts:

• Irrigation water can add large amounts of salt to soil
• Water with 500 ppm salts, applied at 4-acre feet - per season, adds 5,420 pounds of dissolved salts to the soil. At a chloride component of 100ppm, 2,200 pounds of sodium chloride will be added to the soil.
• Avocado yield reduces rapidly as chloride increases in irrigation water
• Effects of chloride toxicity show up under water stress conditions
• Avoid short, frequent irrigation cycles, as salts are not leached
• Avoid prolonged saturated soils, or standing water, that leads to root rot
• Optimal irrigation requires uniform water application and mass, in a large, low-EC zone, under trees
• Drip irrigation is not ideal for managing salinity in hot, dry weather, as it only supports roots in a narrow zone of low EC soil

Avocado grove leaching facts:

• A sign of poor soil leaching is a tree displaying water stress, despite wet soil
• Soil water of about 4 EC, or TDS of 2000, is too salty, as water will leave roots
• Effective leaching requires monitoring soil water to determine irrigation volume and duration
• Generally aim to use a 10-20% leaching fraction at each irrigation, to maintain a root-zone salinity of soil water below EC 2
• Leaching fraction is the amount of additional irrigation water needed to maintain the correct salinity; this, however, depends on salt levels in irrigation water
• Appropriate leaching amounts depend on irrigation water salinity and target root-zone salinity.