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.
