Walnut Orchard Recovery following a Single Drought Year

To evaluate the effects of limited water supplies on production, a one year drought was simulated in 1989 on mature conventionally spaced cv. Chico walnuts. Controlled deficit irrigation (CDI), an irrigation strategy that imposes water deprivation during stages of the season when the trees are considered most tolerant of water stress, was used to apply 16 acre-inches/acre (hereafter referred to as inches). CDI yield in 1989 was not significantly different than the fully irrigated (41 inches) control. Individual nut weight was slightly lower and vegatative growth was much less. In 1990, the old CDI trees were returned to full irrigation but the yield was reduced by about 80% relative to the control. This was due to fewer fruiting positions presumably caused by less shoot growth the previous year. Shoot growth in 1990 in the old CDI trees was greater than the control. Production levels in the old CDI trees returned to normal in 1991. This indicates that 'Chico' walnut trees have the potential for a quick recovery from waterstress related yield losses. It must be emphasized that this was facilitated by the absence of any secondary problems such as diseases or pests that can infest a water stressed orchard.