Almond Facts, May-June 2021

IN YOUR ORCHARD increase. Target SWP is -6 to -10 bars for low tree stress (just above baseline values) and -10 to -14 bars for mild tree stress. It may be impossible or excessively expensive to maintain the low stress levels listed (-6 to -10 bars), but mild water stress should not reduce yield. In young orchards, where possible, avoid extended periods (weeks) of SWP readings more negative than -14 bars as this will shut down shoot growth. Should you practice hull split Strategic Deficit Irrigation (SDI), especially this year ? In SDI, irrigation is reduced (not stopped) to allow a moderate level of stress (-14 to -18 bars) to develop during initial hull split and then the orchard is returned to full irrigation heading into harvest. This practice is reported to save water and not significantly impact yield. A key outcome of hull split SDI strategy is depleting soil water reserves to allow for tighter (shorter) hull split timing and ease of shaking. In a drought year, hull split SDI may not be necessary to achieve this and if tried under limited water conditions might cost growers in reduced kernel weight due to excessive water stress. I suggest a careful reading of David Doll’s honest and thought-provoking post from last summer ( www.thealmonddoctor.com/2020/07/19/ regulated-deficit-irrigation-application/) to help growers and CCAs working with them to decide on the best course of action this year as hull split approaches. Nutrition Timing is critical to efficient nitrogen (N) fertilization in almonds. Nitrogen deficiency reduces flower formation this year and production next year. Too much N means excessive shoot growth, more wind damage risk, higher hull rot risk in the orchard and potential for excess N leaching as nitrate. April and May are the don’t-miss months for N fertilization. By late May into early June (depending on the year) nut N demand eases and hull rot risk rises with increasing orchard N status. Nitrogen nutrition and hull rot are related; the more N in the trees, the higher the hull rot risk. The target window for summer leaf N levels is 2.2–2.5% — adequate but not excessive. Hull rot incidence can increase rapidly with each 0.1% increase in leaf N over 2.5% N. Should N be applied after kernel fill (late May/early June) ? If the fertility program follows a “spoon feeding” approach using frequent, low rate applications to just match N need through the season while keeping orchard N levels low (2.3–2.5% leaf N), then continuing that approach into hull split should work without spiking hull rot. Orchards don’t require much N after kernel fill compared to spring. For example, a 2,500 kernel lb/acre producing orchard only needs additional 20–30 lb N/acre in the tree between kernel fill and leaf drop. So, if an almond orchard N fertility program follows a plan similar to a “snack through the day” diet for a human, then snack on. If the program is more similar to a three square meals plus dessert diet, skip the dessert (late May/early June N application) to limit excessive orchard N levels and reduce hull rot risk. Well water may contain significant amount of nitrate that should be included in fertilizer calculations. See the table in the March-April edition of this column or Table 1 in the Almond Board’s new Nitrogen Best Management Practices (www.almonds.com/sites/default/files/2020-12/ABC_ Nitrogen_8.5x11_vmags.pdf). While N use in almonds peaks in May and eases in June, potassium (K) use continues at a steady rate until hull split. Keep up with (K) nutrition this year to maintain good yields next year. Nut fill. Photo credit: Franz Niederholzer 4 8 A L M O N D F A C T S