Leaf sampling is the most important tool pecan growers have for determining their fertility needs. While soil samples are helpful for checking soil pH and determining any potential problems with competitive uptake between nutrients in the soil, leaf samples tell you the fertility status of the actual trees.
Using soil and leaf samples together allows growers to match their fertilizer applications with the actual needs of the tree rather than just shooting in the dark. This provides an excellent opportunity to save money on fertilizer cost.
Concentrations of mineral nutrients in the leaves change as leaves emerge, expand, and finally senesce in the fall. For many elements, the least change in concentration occurs from early July-early August. For this reason, the general recommended period for leaf sampling is July 7-August 7.
Leaf samples should be taken at this time because critical levels established through experimentation and observation are based on sampling done during this period.
Following are the steps for taking leaf samples:
- Collect 50-100 middle-pair of leaflets from the middle leaf of this year’s growth (See figure above). Use terminal shoots exposed to the sun. Avoid twigs from the interior of the tree. Collect leaflets from all sides of the tree. Avoid leaflets damaged by insects and diseases.
- Abnormal trees or trees not representative of the area should be sampled separately. A complete and accurate description of abnormalities should accompany such samples.
- Sample trees of the predominant variety in a given block. If Schley is the main variety, sample Schley; if Stuart is the main variety, then sample Stuart, etc.
- Immediately upon collection, wipe leaves (entire surface, both top and bottom) with a damp cellulose sponge or cheese cloth to remove dust and spray residue. Do not allow the leaves to come into contact with rubber or galvanized containers. Partially air dry and place in the large envelope of the mailing kit.
- If recent soil test data is not available, it would be advisable to collect a soil sample and have it sent to a soil testing laboratory. By sampling the same trees each year, growers can more readily see the results of any changes to their nutritional programs.