First Year Recovery following a Simulated Drought in Walnut

A one year drought was simulated in 1989 on mature conventionally spaced cv. Chico walnuts. A controlled deficit irrigation (~DI) regime was used to apply 16 inches of water for the season. Yield in that year was not significantly different than fully irrigated (41 inches) trees. The CDI trees were returned to full irrigation in 1990. This year, nut yield was dramatically lower due to about an 80% reduction in nut load. The one year delay in a negative impact on production was presumably due primarily to carryover effects of reduced stress year shoot growth that limited the number of fruiting positions in the following season. This study illustrates that . maintaining production during a drought year does not indicate success in overcoming limited water supplies. Success of CDI must be measured over both the drought and fOllowing seasons. Walnut production responds negatively to CDI--severe water stress cannot be tolerated.