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Pecan Leaf Sampling

PecanGrove

Here are some comments from Lenny Wells concerning leaf sampling:

The time for pecan leaf tissue sampling has arrived. The recommended  period for this is from July 7-August 7. The reason for this window of time is that the nutrients are at their most stable point here at mid-season. This gives you the best idea of the nutritional status of your trees. Prior to this some nutrients are increasing in the leaf, while others are decreasing and soon several key nutrients will begin declining in the leaf as the maturing fruit acts as a sink. For leaf sampling procedures see the blog below from last July:

Leaf sampling procedures

But, what should you be looking for in your leaf samples? You may get a range of recommendations based on your results depending on the laboratory you use. There have been some recent changes to a few key nutrient threshold levels that you need to be aware of as you look at your tissue results. Mike Smith from Oklahoma State was the lead author on a paper a couple of years ago that re-addressed leaf nutrient concentrations for pecans. His results led to the following recommendations and these ranges are the levels you should go by when making fertilization decisions:

Nitrogen (% ):       2.5 – 3.0

Phosphorus (% )  0.14 – 0.30

Potassium (% )     1.00 – 2.50

Sulfur (%)              0.20 – 0.35

Calcium (% )         0.70 – 1.75

Magnesium (% )   0.30 – 0.60

Boron (ppm)             15 – 50

Copper (ppm)            6 – 30

Iron (ppm)                 50 – 300

Manganese (ppm)    100 – 2000

Zinc (ppm)                 50 – 150

Nickel (ppm)            Greater than 2.5

If trees have a pretty heavy crop load and leaf N is below 2.75, I would recommend the application of another 30-50 lbs N depending on the total amount applied to date. Also, with a heavy crop, K should be around 1.20 because the fruit will begin to pull a lot of K from the leaves as they develop. Its difficult to reach 0.14% on leaf P in many cases. Most of the time soil P is adequate but uptake is a problem. If soil P is sufficient but leaf P is low, applying P as a banded application rather than a broadcast application is more effective in increasing P absorption. Zn levels are often artificially high in commercial orchards due to the application of foliar Zn. There may be nutrient residues present on the leaf  that are not actually present inside the leaf itself. To get a true reading, samples should be washed off with a 0.1% phosphate-free detergent and rinsed in de-ionized water prior to analysis. Since this is not practical for most producers, just know that if you have been spraying foliar Zn or other micronutrients  and get very high results in your samples, it is likely due to residue.