This article originally appeared in the June 2010 Ag News and Views newsletter.
Nutrient management is essential for a successful pecan orchard or grove. With the high cost of fertilizer and the labor required for application, it is critical to accurately account for the nutrient needs of the tree for successful pecan management. Leaf tissue is sensitive to changes in nutrient supply and can serve as an indicator of both limiting and excess nutrients. To ensure accurate analysis, the following procedures should be followed. In addition, samples should be collected from trees located in distinct areas of the orchard or grove to account for different soil types, management strategies and varieties.
Procedure for taking leaf samples:
- Collect samples in July.
- Do not mix varieties unless management for the area will be the same.
- Collect 100-150 middle pairs of leaflets from the middle leaf of the current season's growth (Figure 1). Avoid leaves in the interior of the tree and from suckers, water sprouts or leaflets damaged by insects or disease.
- Do not use galvanized containers, rubber gloves or rubber sponges to collect, carry or store samples.
- Remove spray residue and dirt by washing or dipping the leaves in tap water for less than one minute.
- Dry leaflets after washing by spreading them out to air dry until they will crumble. Do not expose them to direct sun or allow exposure to heat while drying.
- Place dry leaflets in a paper sample bag for transport. Do not send wet leaves or use plastic ziplock bags.
- Accurately and completely identify each sample including the age and variety (improved or native).
Be aware that the laboratory cannot analyze samples of fewer than 100 leaflets.
Once dried, take the samples to your local county extension office for shipment. In Oklahoma, samples will go to Oklahoma State University, and Texas samples will be sent to the Texas A&M Soil, Water and Forage Analytical Laboratory. Currently, each sample analysis will cost approximately $20 and results are typically returned within 14 days. As an alternative, samples can be sent to the Noble Research Institute Agricultural Testing Services for analysis by Servi-Tech Labs in Amarillo, Texas, at a cost of approximately $28 per sample.
Sufficient ranges for nutrients required by pecan trees follow:
0.12 - 0.3 percent
0.75 - 1.75 percent
0.7 - 2.5 percent
0.3 - 0.7 percent
100 - 1000 ppm
50 - 150 ppm
60 - 150 ppm
3 - 15 ppm
2 - 10 ppm
Recommendations will indicate the amount and type of fertilizer needed for each sample. A three- to five-year history of nutrient levels within a given orchard/grove can minimize fertilizer applications.