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	60	90
2.0 to 2.3	50	90
2.4 to 2.5	40	80
Above 2.5	40	60

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

% Leaf P	Recommended P2O5 lbs./Ac
< 0.12	60
0.12 and above	none

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

 

% Leaf K	Recommended K2O lbs./Ac
< 0.75	60
0.75 and above	None

 

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.