Objectives
- Determine the degree to which almond leaf nutrient status varies across a range of representative orchards and environments.
- Validate early season leaf analysis protocols and relationship with yield.
- Validate current CV’s and determine if nutrient ratio analysis provides useful information to optimize fertility management.
- Develop new leaf sampling and interpretative methods for almond nutrition.
Summary of the Experiment
A large-scale and long term survey of within-field, between-field, and between-organ nutrient concentration and variance was conducted in mature almond orchards representative of the major production regions. The interaction between yield and nutrient status is being analyzed on >400 individual trees. All almond trials have been initiated in 8 or 9 years old almond orchards of good to excellent productivity planted to nonpareil (50%).
A standard leaf sampling protocol was used to determine nutrient concentrations in samples of exposed, non-fruiting spurs (NF), as well as leaves from fruiting spurs with 1 and 2 fruit (F1 and F2, respectively) to explore the sensitivity of different sampling methods as indicators of tree nutrient demand throughout the season.
Results & Discussion
The current practice of sampling leaves in July is too late to allow for current season adjustment of fertilization and leaf sampling alone does not provide sufficient information to make fertilizer recommendations. An improved method of leaf sampling and fertilization management has been developed that utilizes April leaf sampling and yield estimations to predict N demand and to allow for in-season fertilizer adjustments
Leaf Sampling Protocol
The following leaf sampling method recognizes that growers generally collect one combined leaf sample per orchard. If the orchard to be sampled has substantial variability, then samples should ideally be collected separately from each zone and N should be managed independently in each of these zones if possible. It is also critical that every orchard that differs in age, soil, environment or productivity should be sampled and managed independently.
Leaf Sampling Procedure
Results demonstrate that April samples can be used to effectively predict both July leaf nutrient status and harvest kernel N status (Table 1 & Fig. 1). Leaf samples collected in April are superior to July samples for use as indicators of tree N status and provide an excellent measure of N removal in crop.
Sampling Instructions
- Sample at 43 days after full bloom, +/-6 days.
- Use almond trees var. Nonpareil, at least 8 years old.
- Identify areas of low performance and collect samples from them independently.
- Collect leaves from 18-28 trees per orchard. Combine all leaves in a single bag for submission to reputable laboratory.
- Sample trees must be at least 30 yards apart.
- In each tree, collect leaves from two fruited spurs from around the canopy, from at least 5-8 well exposed spurs located between 5-7 feet from the ground. A total of 100 to 200 leaves is ideal.
- Send the samples to the lab and request a FULL NUTRIENT ANALYSIS (N, P, K, B, Ca, Zn, Cu, Fe, Mg, Mn, S).
Fig.1. Relationship between leaf N concentration in April and N removal by fruit per 1000 lb of kernel yield. In these trials maximal yield occurred with a leaf N value 3.2-3.5% N in April or 2.3-2.4% N in July.
For more information see the presentations and publications under Outreach