Franz Niederholzer, UCCE Orchard Advisor, Colusa and Sutter-Yuba Counties

Nutrient inputs (fertilizer, amendments, etc.) are expensive. Crop losses from nutrient deficiencies cost the grower even more. For example, fertilizer inputs (nitrogen, potassium, zinc, and B where needed) can run to $500 per acre, but nitrogen (N) deficiency alone reduced almond yield by more than 500 kernel pounds per acre in a UC study. Excess orchard N can increase risk of future crop losses from leaf rust and hull rot and increase sanitation costs after harvest.

A summer (July) leaf sample paired with a hull sample at harvest is an important check on orchard nutrition status, helping deliver the best results from a fertilizer program. Separate samples from each variety in the orchard help keep yields consistent and orchards healthy over time. Leaf analysis costs are roughly a dollar/acre for a 50-100 acre block, and when done correctly, worth far more to the grower.

Following certain steps ensures consistent, accurate results.

• Only sample fully expanded, healthy leaves from non-bearing spurs [Leaves from bearing spurs have lower nutrient levels than leaves from non-bearing spurs.] All the UC research and tables (see Table 1 below) are based on leaf samples from non-bearing spurs. A sample of about 100 leaves is the target volume.
• Take samples from trees at least 90 feet apart from across the orchard where trees of the same variety/rootstock are of similar size and health. If there is a “problem” section of the orchard, take a separate sample for that area and compare the results when the lab report arrives. Some growers and/or PCA/CCAs flag or otherwise mark trees and use those same trees each year to reduce tree-to-tree variability in lab results.
• Keep the leaf samples refrigerated and hand-deliver or over-night express to the lab.
• To check orchard boron (B) status don’t use July leaf samples but grab about a pint of dried hulls from windrows across a field just ahead of pickup and ship to the lab.
• Leaf sample results influence decisions that can run to tens of thousands of dollars per orchard. Therefore, the person pulling the tissue samples should be trained and carefully follow the sampling steps listed above.

Leaf and hull sample results should be reviewed in combination with yield data for the past year as well as notes about orchard health (vigor, etc.) to best evaluate an orchard fertility program for the past year and plan for next year. Remember that half the trees in the orchard are below and half are above the value shown on the nutrient report. Given this, an article last year argued that 2.4% N should be the goal on the July report.

Table 1. Critical nutrient levels for almond leaves sampled in July (from fully expanded leaves on non-bearing spurs) and almond hulls sampled at harvest (modified from table in Almond Production Manual; UC ANR Pub. 3364) plus almond crop nutrient use per 1000 pounds of kernel crop.

The crop nutrient use data presented here are taken from this source: Final Report 2008-13 CDFA Fertilizer Research and Education Program, 10-0039SA, Project Leader: Dr. P.H. Brown, UC Davis Department of Plant Sciences