Thursday, August 22, 2013

Interpreting pecan leaf analysis results

    Annual nut production is only possible if pecan trees have a sufficient supply of soil nutrients available for uptake by tree roots. Mid-summer leaf analysis is the best way to assess the nutritional status of pecan trees and to determine the fer­tilizer needs. Table 1 provides the major and minor nutrient sufficiency ranges for pecan trees grown for nut production. Tables 2-4 provide fertilizer recommen­dations for the major nutrients based on leaf test results. At the minimum, pecan trees require annual applications of nitrogen fertilizers twice a year—in early March and again in early October.  If potassium and phosphorus fertilizers are needed a single application can be made in the Spring (March).
Table 1. Leaf Elemental Concentration Sufficiency Ranges for Pecan Orchards

N%               2.4-3.0
P%               >0.12
K%               0.75-1.00
Ca%             >0.7
Mg%            0.3-0.6

Zn ppm         >60
Fe ppm         >50
Mn ppm        >100
B ppm          20-45
Cu ppm        >7

Table 2. Nitrogen fertilizer recommendations based on leaf test results. Nitro­gen fertilizers should be applied both Fall and Spring every year.

Pounds of actual N to broadcast per acre
% Nitrogen in leaf samples
October application
March application
below 2.0
2.0 to 2.3
2.4 to 2.5
Above 2.5

Table 3. Phosphorus fertilizer recom­mendations based on leaf test results. Phosphorus fertilizers should be applied in the Spring.

% Leaf P
P2O5 lbs./Ac
< 0.12
0.12 and above

Table 4. Potassium fertilizer recommen­dations based on leaf test results. Potassium fertilizers should be applied in the Spring.


% Leaf K
K2O lbs./Ac
< 0.75
0.75 and above

Correcting Other Common Nutrient Deficiencies

Magnesium.  When leaf levels drop below 0.30%, add a magnesium con­taining fertilizer to the soil at the rate of 20 lbs Mg/ Acre. Magnesium containing fertilizers include magnesium sulfate, magnesium oxide, K-Mag, Sul-Po-Mag and kieserite. Dolomitic lime can be used in acid soils needing a pH adjust­ment. High N and K fertilization rates can lead to Mg deficiency.

Zinc. Zinc deficiency problems  (leaf Zn < 60ppm) most commonly encountered on sandy, soils low in organic matter or soils with a pH above 7.2. Increasing the organic matter in soils and adding Zinc sulfate to the soil at the rate of 5-10 lbs. ZnSO4 / Ac. is recommended for acid infertile soils. In high pH soils, zinc must be applied annually as a foliar spray. Growers should mix 2lbs of ZnSO4 per 100 gal of water (or use commercially prepared liquid Zinc prod­ucts) and spray their trees starting at leaf burst. Three to five sprays are needed and should be made at 2 week intervals.