Understanding Pecan Irrigation

Understanding Pecan Irrigation

Water, particularly where nut quality is concerned, has more of an effect on pecan production than any other factor. Drought stress affects nut size and filling, as well as leaf and shoot growth. Adequate soil moisture is important at bud break in order to stimulate strong, vigorous growth, from bloom through shell hardening for nut size, and during the nut filling stage for optimizing kernel percentage. If trees do not receive adequate soil moisture levels late in the season, shuck split and energy reserves are affected. Pecan trees extract most of their water from the upper 32 inches of the soil profile. Though they are deep-rooted, most of the deep water available to the tree is survival water and is not useful for fruit production. The deeper the available water, the more energy the tree must expend to obtain it. As energy is diverted from the leaves and nuts, the tree will shed leaves, drop nuts, or only moderately fill the pecans. The nut sizing period normally occurs from May 1 through August  15. Although, not a critical water use stage for the pecan, serious drought conditions during this period can affect yield. The most common visible effects of an extended drought during this period are excessive nut drop at the two and three leaf stage and “shell hardening” on small nuts. Additionally, lack of sufficient water during the nut sizing period causes small nuts and may lead to physiological split of the nuts resulting from a sudden influx of water during the nut filling stage insome varieties. The nut filling stage occurs from August 15 to the first week of October. The most critical period for water use is during the first two weeks of September. Lack of sufficient water during the nut filling stage will lead to poorly filled nuts, which will result in poor nut quality.

Irrigation systems should be in operation for 12 hours (or less) per day in order to prevent water logging and oxygen depletion in the root zone.  Also note that irrigation systems can be turned off for 3 days following rainfall events of  1” or more.  We know that young, non-bearing trees (<5 yrs old) do not require anywhere near the amount of water applied to mature trees in late season. The April or May rates applied to mature trees will work season long for young trees because there is no crop demand on them.