Horticulture: September 2006 Other Horticulture Articles

After returning from the Oklahoma and Texas pecan growers association meetings where water management was a topic of discussion, I felt the need to write about pecan water management. I have participated in several drought seminars and received numerous calls from cooperators concerning water-related issues. I have been asked many times about how the drought will affect pecan production this year.

Pecan grove on Noble's Red River Farm

Water stress can create a number of problems with pecans. Water is crucial in different stages of development in pecan production, beginning with shoot growth (late March and early April), crop set (early-mid May), nut sizing (June-July), kernel fill (late July through September), shuck split (October) and, finally, next year's crop.

Any stress on the tree in the late development stage can result in major fruit drop. Late-season water stress can cause leaf drop and impair shuck opening (sticktights). Longterm stress like that from the current drought can cause reduced crop set the following year, branch die-back and even tree death.

Many people have asked how much water a pecan tree requires. There have been estimates of about 55 inches of water a year (Miyamota, 1983). However, some estimates are as low as 30 inches per year (McEachern, 1982), and other estimates as high as 72 inches per year.

If we say a mature pecan tree requires 55 acre-inches per year, and most of this water is used during the growing season (April through October or 225 days), the daily water use can be predicted as follows:

55 acre-inches per year x 27,154 gallons per acre-inch = 1,493,470 gallons per acre per year
1,493,470 gallons ÷ 225 days of growing = 6,638 gallons per acre per day
6,638 gallons ÷ 35 trees per acre = 190 gallons per tree per day

The standard recommendation for water requirements of pecan trees is 1 to 2 inches per week and can be calculated into daily water requirements like this:

1 acre-inch x 27,154 gallons per acre-inch ÷ 7 days = 3,879 gallons per acre per day
3,879 gallons per day ÷ 35 trees per acre = 111 gallons per tree per day
(Stein, 1994)

Remember, trees get water from the soil, and the deeper the soil, the greater the water-holding capacity. For example, a tree growing in a soil 7 feet deep has the potential of 9,000 gallons of available water per tree compared to a 7-inch-deep soil, which has the potential of only 800 gallons of available water per tree. Therefore, for a mature tree that uses 100 gallons per day, the 7-foot soil can supply water for 90 days while the 7-inch soil can supply water for only eight days (McEachern, 2006). Another factor that plays into water-holding capacity is the soil type. Sandy soils have less waterholding capacity than loams or clay soils. So, a 7-foot loamy soil holds more water than a 7-foot sandy soil.

Therefore, starting the season off with a full soil profile is important, as is receiving rainfall or using irrigation to provide the recommended water requirement.

For more information about irrigation systems and scheduling irrigation application, look for future articles or contact us at (580) 224-6500 if you have any immediate questions.

References
McEachern, G.R. 1982. Pecan water requirements, p.112. In: G.R. McEachern (ed.) Texas Pecan Handbook. Texas Agricultural Extension Service, College Station.

McEachern, G.R. 2006. Pecan water management without irrigation. Pecan South Vol. 39:3.

Miyamota, S. 1983. Consumptive water use of irrigated pecans. J. Am. Soc. Hort. Sci. 108:676-681.

Stein, L.A. 1994. Irrigation management for pecans p. 144. In: Smith, M.W., William Reid and Bruce Wood (eds) Sustaining Pecan Productivity Into the 21st Century: Second National Pecan Workshop Proceeding.

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