Annual nut production is only possible if trees have a sufficient supply of soil nutrients available for uptake by their roots. When severe enough, nutrient deficiencies can results in visible changes in leaf and leaflet size and coloration. Chemical analyses of foliage nutrients, however, are a more reliable method to detect deficiencies when they are more easily corrected.
Using proper sampling techniques is critical for making leaf analysis a valuable management tool. Pecan and walnut leaf samples should be collected during mid-summer (late June or early July). You should collect a composite sample of leaflets from several trees that are growing in similar soil conditions. The sufficiency ranges to be reported in the next issue of the newsletter are usually based on collecting the middle pair of leaflets on the middle leaf of the current season's shoot growth (fig. 1). Only one pair of leaflets should be collected per shoot. Each sample should be composed of at least 50 pairs of leaflets sampling shoots on more than one tree. If leaflets are covered with dust or spray residue, rinse the leaflets in tap water.
Immediately after collecting, spread leaflets out to air dry away from direct sunlight until they become brittle. Leaflets can also be spread out on a clean cookie sheet and dry in an oven at 130 oF for 24 hours. Place brittle leaflets in a clearly labeled paper bag that includes your name, address, and identifies which orchard or part of an orchard the sample was taken.
Dried leaflets will need to be sent to a commercial laboratory capable of analyzing plant tissues for N, P, K, Ca, Mg, and Zn with options for Mn, Fe, B, Cu, and S if there is no additional charge. The University of Missouri Soil and Plant Testing Laboratory charges $25.00 per sample and will provide an interpretation of the results and their recommendations for correcting deficiencies. Information, forms, instructions for submitting samples, and accepted methods for payment are available at their web site at http://soilplantlab.missouri.edu/soil/.
An alternative is the Arkansas Diagnostic Laboratory at the University of Arkansas that will provide similar analyses for $21.60 per sample for out-of-state customers. While a little less expensive, be aware that they do not provide an interpretation of results or recommendations for correcting deficiencies. Air-dried leaflet samples clearly marked with name, address, fax number or email should be sent along with payment and note for "total analysis" to Agriculture Diagnostic Laboratory, 1366 W. Altheimer Dr, Fayetteville, AR 72704 (ph: 479-575-3908).
After you receive the results of the nutrient analyses, you have several options for interpreting the results. If you use the UMC Soil and Plant Testing Laboratory, they will provide an interpretation and their recommendations for correcting deficiencies. You can also consult published references that give the sufficiency ranges (concentration range over which trees may or not respond to an application of that nutrient) for pecan and walnut and do your own interpretation. Sufficiency ranges for northern pecan and black walnut will be summarized in the next issue of the newsletter along with recommendations for correcting deficiencies in northern pecan.
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Webmaster's Note: Part 2 of this article was published on August 15.
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* William Reid is an Assistant professor at the University of Kansas and is an agent at the Kansas Extension Service. He is the author of many books about fruits and nuts.
Dr. Jerry VanSambeek is a research plant physiologist at the USDA Forest Service. He can be reached at jvansambeek@fs.fed.us.
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