Irrigation - Why, When, And How Much ?

Why Irrigate ?

This should seem obvious but here's a quick review.

• To establish good root systems in new plantings of orchards and vineyards,
• To reduce stress on plants to increase orchard and vineyard life,
• To improve plant hardiness heading into winter,
• To enhance growth and shoot length increasing the supply of carbohydrates,
• To ensure flower bud initiation and sufficient blossoms for the following year,
• To assist in the uptake of nutrients to reduce nutrient deficiencies,
• And to increase fruit size, marketability and overall crop yield.

When do you need to irrigate ?

There are too many factors to list to come up with a precise schedule. Most growers will start in mid June depending upon the crop, the soil type and the rainfall to date. "Feel" testing is one simple method to determine whether the soil needs irrigation. At 50% of saturation (or field capacity), clay and clay loam soils will be somewhat pliable and will form balls under pressure when squeezed in the hand. Sandy loam soils will appear to be dry and will not form a ball under pressure.

Another method is to determine field capacity in the spring after a heavy rainfall, which brings the soil reservoir to the saturation point. Then subtract the daily use water of the crop from the total available water in the root zone until the irrigation point is reached (50% of the crop available soil water).

Samples of average daily water use for mature trees and vines:

Peach/Pear (mm per day)
May : 2.5
June : 4.1
July : 5.1
August : 4.0
Sept. : 3.0

For tender fruits it should be noted that there are two key times for irrigation, cell division right after June drop, and cell expansion, a few weeks before predicted harvest. The critical irrigation period for grapes is from berry set through the ripening period (veraison). Avoid irrigation in September to maintain sugar levels and reduce the probability of late growth and winter injury unless under severe stress.

How much do you irrigate?

A general rule of thumb for tender fruit trees under "normal conditions" would be 25 to 38 mm (1 to 1.5 inches) per week early in the season and 38 to 50 mm (1.5 to 2 inches) during final swell. Also, each mature tree requires 36 litres (8 Imperial gallons) of water per day during July and August. Avoid extended dry periods combined with excessive volumes of water to replenish soil moisture with peaches early in the season to reduce the incidence of split pits.

| Top of Page |