Spring Leaf Sampling for Pistachios
When leaf nutrient concentrations are at or below the critical values, yield will be 90% or less than the maximum and deficiency symptoms will start to develop. Therefore, the practice of only sampling leaves in July is too late to allow for in-season adjustment of fertilization practices if needed due to nutrient deficiencies. When the nutrient concentration is in the suggested range, tree growth and yield should be optimal provided other growth parameters are not limiting.
The importance of sampling in Spring (mid-May)
Leaf sampling is valuable and provides information on the current status of the tree and the effectiveness of grower’s management decisions. July (summer) sampling can be done to monitor plant N status and make end-of-year adjustments while sampling done in mid-May (spring) can help predict seasonal nitrogen or potassium demand. The predicted values can assist growers better plan their nutrient management before any symptoms of nutrient deficiency occur or to adjust an existing program.
Recommended Sampling Criteria
For each orchard/block or sub-block that you wish to have individual information on, do the following:
· If variable, divide your orchards into uniform blocks and take separate samples for each block (approximately 20 acres).
· Collect leaves from 18–20 trees per block.
· In each tree collect 10 leaves around the canopy located between 5-7 feet from the ground.
· Collect sub-terminal leaves only from exposed, non-fruiting branches.
· Combine all leaves in a single bag for submission to a reputable laboratory. Each sampled tree must be at least 25-30 yards apart.
· A minimum of 180 leaves per sample bag is required.
Interpreting the results
Recent research has resulted in the Pistachio Prediction Model, which uses nutrient analysis of spring leaf samples collected in May, usually 30 to 45 days after full bloom, to predict late summer nutrient concentrations of N and K.
The concentrations of all analyzed nutrients and the time of sampling (days after bloom) can be entered into the Pistachio Prediction Model, which can be found here. The predicted summer (July or August) N and K concentrations can be interpreted as described for samples taken in July. (Critical level: N = 1.8%, K = 1.6%; Suggested level: N = 2.2 to 2.5%, K = 1.8 to 2.0%).
Leaf nutrient concentrations change during the season and may differ between leaves on the same tree depending on their location. The values mentioned above are based on leaves sampled from late July through August following the sampling procedure outlined previously. It is important to note that if leaf samples are being taken for diagnosing any growth disorder, they can be taken at any time of the year and samples should be taken from both affected trees and normal trees. Trees should be of the same age, scion type and rootstock if you are comparing the results.