"since leaves are the important synthesis centers of plants, tests of leaves more nearly reflect the nutritional status of the plant than do tests made on the soil."--Westwood, Temperate-zone Pomology. With all the excitement of harvest it is easy to overlook taking annual leaf samples for tissue analysis. Late summer leaf analysis is an essential routine procedure in modern orchards, providing information on the nutritional status of trees relative to a set of general nutritional ranges. If combined with soil samples taken every three to five years, annual leaf analysis can be an excellent management tool.
Why use leaf analysis?
Leaf analysis, if used routinely, provides a historical reflection of fertilizer management as it relates to yield and fruit quality. Leaf tissue analysis can be used to estimate fertilizer needs for next season, thus avoiding deficiency or toxicity problems. It is also a useful tool to diagnose nutrition problems effecting post harvest quality.
When and how do you take the sample?
Sample mid-July through August once active growth stops. Leaves should be sampled from current season, mid-terminal, upright (but not vertical) branches after terminal bud formation. Generally, leaves are picked at shoulder height from the fruiting framework of the trees. Around 50 leaves should be selected randomly from no more than five acres of the same variety, strain, rootstock, training method, soil type and irrigation block.
Limitations of leaf tissue analysis
As stated above, leaf analysis provides growers with data on the nutritional status of their trees relative to a set of general guidelines provided in range tables. Sometimes the 'optimum' or 'critical' levels of a nutrient in a range table are not the best for a particular orchard. For example a Golden Delicious orchard with a severe bitter pit problem may need less nitrogen in the tissue, even if the leaf analysis indicates a level of 2.0% N which is in the upper end of the 'optimum' range for this variety.
Nutrient range tables for new varieties and training techniques are limited. This does not mean that growers should not collect leaf samples from these blocks - the opposite applies. The more data the tissue analysis labs can collect and analyze from new varieties, training techniques and locations, the faster the development of our knowledge on the best fertilizer regimes required for these varieties. Contact your local analytical laboratory before collecting leaves so that the samples meet their requirements.
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Tree Fruit Research & Extension Center, Washington State University,1100 N Western Ave., Wenatchee, WA, 98801 USA
Wenatchee WA, 20 August 1996