A leaf sample is far more accurate than a soil sample in determining the amount of essential minerals being absorbed from the soil. A leaf sample will indicate the level of soil-supplied minerals and is the best means of accurately establishing nitrogen and zinc levels. These two nutrients, in addition to potassium, are the three elements most often deficient in Louisiana pecan orchards.
Leaf samples are extremely useful when taken properly. For trees that are producing well, a leaf sample can detect deficiencies in the non-visible range often referred to as “hidden hunger.” Corrective action can then be taken before the appearance of visual deficiency symptoms and in time to avoid an adverse effect on production.
Soil sampling is still recommended, however, to determine soil texture, certain mineral levels or imbalances, soil pH and any toxic mineral levels. It is also the only means available to determine fertility needs in new plantings. Both methods should be used initially, although subsequent soil samples need not be taken as often as leaf samples.
Pecan leaf analysis should be made in July. Collect the middle pair of leaflets from the middle leaf of the current season’s growth. Take samples from shoots that have terminated their growth for the season and have fully expanded leaves. Continue this procedure until 40 pairs of leaflets have been collected from at least 10 trees. This constitutes one sample. Select shoots that are fully exposed to the sun and near the ends of branches, not small branches arising from large limbs nor shaded branches near the center of the tree. Collect from all sides of the trees. Avoid taking leaflets damaged by insects or diseases or those that are otherwise contaminated. Leaflets in one sample should all be from one variety, but this is not essential.
Samples from trees that are dying or otherwise not typical of the average orchard tree should not be included with the regular samples. It is also advisable to keep samples from young, non-bearing trees labeled separately from samples of older, bearing trees. Avoid sampling leaves covered with dust such as those near dirt roads, etc. Place the leaves in a new, clean paper bag for air-drying in a dust-free area. Leave the bags open until leaves are dry. Leaves can also be dried in a kitchen oven overnight with the oven set on warm. Do not send in fresh green leaves.
If major rains have not followed the last zinc application, rinse the leaves in running water and swipe with a damp cloth before drying.
Avoid rubber and galvanized containers when collecting leaves, because these could affect results.
The nutrients normally analyzed are: nitrogen, phosphorus, potassium, magnesium, calcium, sulfur, zinc, iron, manganese, boron, copper and molybdenum. Local state university laboratories performing pecan leaf analyses include:
Plant Analysis Laboratory
LSU Department of Agronomy
126 MB Sturgis Hall
Baton Rouge, LA 70803-2111
Agriculture Chemistry Laboratory
Agricultural Chemistry Building, room 102
LSU Highland Rd.
Baton Rouge, LA 70803
(Indicate "Pecan Plant Tissue Group" on sample)
MSU Soil Testing & Plant Analysis Laboratory
Mississippi State, MS 39762
Extension Soil, Water and Forage Testing Laboratory
Texas A&M University
College Station, TX 77843-2474
Samples can be sent directly to the laboratory and the results of the nutrient analysis will be returned directly to the grower with an adequate, deficient or excessive rating given to each nutrient. If you have questions on the results, contact your county agent.