sampling leaf tissue in April, select all the leaves from
five to eight nonfruiting, well exposed spurs per tree, as
indicated here by tags.
The traditional practice of sampling almond leaves in July in order to determine fertilizer rates and timing is too late to allow for in-season adjustments that match the crops’ needs. But new research shows that sampling leaf tissue in April, approximately 43 days (plus-or-minus six days) after full bloom, allows growers to combine yield estimates and leaf-sampling results to predict nitrogen (N) demand, and then adjust the May-through-July fertility program accordingly.
This new protocol is the result of four years of research supported by the Almond Board of California and USDA, and led by UC Davis plant scientist Patrick Brown. Trials were conducted at multiple sites and were validated in additional trials in 2012. The goal of the new protocol is to ensure that N fertilizer rates target individual orchard productivity for the current crop year. By applying only as much fertilizer as the crop demands, growers can save money and reduce the risk of leaching or off-gassing of excess nitrogen.
If yields are expected to be off in one season and the April leaf analysis shows adequate N, the mid-season N application could be reduced. But if higher-than-expected yields are anticipated, an increase in N fertilizer may be called for.
Guidelines for the April leaf sampling, including collection technique, what the analysis should include, and how to interpret the results to plan a fertility program for the rest of the season, are provided in the document “Almond Early-Season Sampling and In-Season Nitrogen Application Maximizes Productivity, Minimizes Loss.”
The guidelines follow the UC Davis Early-Sampling Protocol, or UCD-ESP. When submitting samples to your lab, be sure to ask for the UCD-ESP. All California testing laboratories will be provided with UCD-ESP guidelines for interpreting April tissue values.