Nutrient Management Research Database
General Information
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Summary/Abstract from Original Source
Potassium (K) fertilization of pistachio trees in the Central Valley of California substantially increased both nut yield and quality during a three-year study. Results indicated that the presently suggested leaf K critical level of 1.0 percent should be increased to 1.7 percent or higher.
Research Highlights
Design and Methods
This study investigated the effects of potassium (K) fertilization on leaf K concentration, nut yield, and pistachio quality.
There were three study locations: Madera, Yolo, and Orland, CA. All orchards were of the 'Kernan' variety.
K was applied at rates of 0, 120, 240, and 360 lbs K2O per acre applied as potassium sulfate (K2SO4)
Initial available soil K in the top 0-6 inches of soil was 82, 97, and 125 in the Madera, Yolo, and Orland sites respectively.
Results
Leaf K Concentrations
K fertilization reliably increased leaf K concentrations. In all but a single case, no differences in leaf K resulted from applying more than 120 lbs K2O per acre.
Leaf K uptake is low at the start of the season, and increases as fruit development proceeds from July-September. Maximal K demand occurs at the end of this period, and declines rapidly following harvest.
K Fertilization Increases Yield
0 lbs K2O/A | 120 lbs K2O/A | 240 lbs K2O/A | 360 lbs K2O/A | |
Yolo | 1223 lbs/A | 1567 lbs/A | 1823 lbs/A | 1695 lbs/A |
Madera | 1934 lbs/A | 2806 lbs/A | 3179 lbs/A | 2802 lbs/A |
Orland | 1963 lbs/A | 2619 lbs/A | 3136 lbs/A | 2659 lbs/A |
K fertilization reliably increased yields when additions ranged from 0-240 lbs K2Oper acre. However, further increasing K application to 360 lbs K2O per acre decreased yields.
K Fertilization Increased Nut Quality
Higher percentages of split nuts, higher 100-nut weight, and lower percentages of blank and stained nuts resulted from K fertilization. However, no differences were seen between the different levels of K added.
Diagnostic Criteria for K Nutrition
A critical value of 1.67 to 2.02 leaf K% was identified as a level to attain 95% of maximum yield.
Recommendations
Pistachio orchards should be fertilized at a rate of 120-240 K2O/acre in California.
Additional Information
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