Revised Nutrient Sufficiency Ranges and Fertilizer Guidelines for Pecan Michael Smith – Oklahoma State University Charles Rohla – Samuel Roberts Noble Foundation Bill Goff – Auburn University
Is a managed nutrition program important? • Maintaining a balance among nutrients is essential. • Excessive application of a nutrient will not increase growth or production, but will increases cost and may cause other problems. • Shortages reduce growth, yield, cold hardiness and the ability to cope with stress.
Why leaf samples? Represents nutrients available and absorbed by the tree. Leaf elemental concentrations are closely correlated with tree performance. Why not soil samples? Frequently little, if any, correlation between soil test levels of nutrients with tree performance or leaf elemental concentrations. Primary value of soil sample is pH and to diagnose problem areas.
When and what to sample? • Leaves from the 1st growth flush that are fully expanded, but before nut nutrient demand increases. • Typically July. • Collect – the middle leaflet pair from the middle leaf on sun-exposed shoots. • Sample ≈100 leaflet pairs representative of the orchard.
Are elemental sufficiency ranges among locations similar? • Physiological nutrient requirement for pecan is not affected by geographic location. • Little effect of yield on nutrient requirement.
Native & low-input orchards vs. high-input orchards • Native and low-input orchards are: • Less productive • Lower nut value • Fewer inputs such as irrigation, crop load rarely managed, less pest control, greater damage tolerance. • Marketed to shellers vs. “gift-pack” and international markets.
Nitrogen – Native & low-input <2.3% Low. Double last year’s N application rate. If the orchard did not receive N last year apply 150 lb/acre N. 2.3% to 2.5% Normal. Optimum. Continue present N application rate. 2.5% to 2.7% Normal. Nitrogen application can be reduced without affecting yield or nut quality. Decrease the application rate by 20%. 2.7% to 3.0% Normal. Nitrogen application can be reduced without affecting yield or nut quality. Decrease the application rate by 50%. >3.0% Above normal. Withhold all N for 1 year.
Nitrogen – High-input orchard <2.3% Very low. Double present N application rate. 2.3% to 2.4% Low.Increase the present N rate by 30%. 2.4% to 2.7% Normal. Optimum.Continue the present N application rate. 2.7% to 3.0% Normal. Nitrogen application can be reduced without affecting yield or nut quality. >3.0%Above normal. Decrease application rate by 50%.
Nitrogen application factors • Greatest demand • ≈ 3 weeks after budbreak, late water stage. • Urea - problem with N volatilization • Temperature > 70oF, moist soil, high pH • Requires at least ¼” of rain or irrigation to incorporate • Sandy soils or flooding potential • Split application beneficial • Pre-budbreak & late-May • Pre-budbreak to mid-May & late water stage • Ground cover • Legume may supply all the N needed • Non-legume: applying pre-budbreak appears to favor tree • Application in the weed free area surrounding the tree • Injection of liquid N into drip or micro-sprinkler system • Minimizes N loss, flexible, economical to use multiple N applications • Up to 50% N reduction without loss of tree performance
Phosphorus Native & low-input orchard High-input orchard < 0.14% Low ≥ 0.14% Normal • < 0.12% Low • ≥ 0.12% Normal Apply as a banded application (100 to 150 lb/a P2O5) within the wetted zone if irrigated. Otherwise, about mid way between trunk and canopy periphery. Pre-budbreak & late water stage have both been effective. May have faster response from late water stage application.
Potassium Native & low-input orchards High-input orchard < 1.0% Low. ≥ 1.0% Normal. • < 0.85% Low. • ≥ 0.85% Normal. Apply as a banded application (100 to 150 lb/a K2O)within the wetted zone if irrigated. Otherwise, about mid way between trunk and canopy periphery. If both phosphorus and potassium are needed they can be blended and applied together. P & K symptoms look alike. P symptoms may develop relatively early in the growing season, as above. P symptoms more likely as nuts fill.
Other macro-nutrients • Sulfur • < 0.20% Correct with using (NH4)2SO4 for N and ZnSO4 foliar application for Zn. • Calcium • < 0.70% Apply lime based on soil test with target of 6.8 pH. • Magnesium • < 0.30% Soil test and if pH low adjust with dolomitic lime. Otherwise use MgSO4 at manufacturer’s recommended rate.
Boron In Georgia, foliar B application applied beginning during pre-pollination increased fruit retention and kernel % of ‘Desirable’. < 15 ppm Apply 3 foliar applications of Solubor (20.5% B) at 0.5-1.0 lb/acre of material. Begin as the 1st leaf unfurls during budbreak, and then twice more at 2-week intervals. 15 ppm to 300 ppm Normal, none needed. > 300 ppm Excess. Determine source, usually irrigation water, and correct.
Manganese < 100 ppm Apply 3 foliar applications of MnSO4 (32% Mn) at 6 lbs/acre of material. Begin as the 1st leaf unfurls and then twice more at two week intervals or with the 1st and 2nd generation pecan nut casebearer sprays. MnSO4 and ZnSO4 can be tank mixed and are compatible with most pesticides.
Zinc • < 60 ppm • Bearing trees ― 3 application of ZnSO4 at 3 to 6 lbs/acre of material at as 1st leaf unfurls, 1st generation PNC and 2nd generation PNC. If severe or high-input add an application between budbreak and 1st generation PNC. 40 ppm is adequate if foliar Zn not applied, especially for native and low-input orchards. • Non-bearing ― ZnSO4 at 1 to 2 lbs/100 gal of material as 1st leaf unfurls and then at 2-week intervals as long as new growth is present.
Iron Heerema et al. • < 50 ppm Cool, wet springs can induce an Fe deficiency that is corrected when conditions improve. • If deficiency acute or persists 2 years use a foliar applied Fe Chelate or a soil applied EDDHA Fe Chelate.
Copper and Nickel Copper Nickel < 2.5 ppm apply Nickel Plus or Nickel CBM foliarly Frequently associated with old orchard sites with sandy soils, particularly those soils with marine origin. • < 6 ppm Copper is rarely deficient. Use either CuSO4 or Cu Chelate.