Fertilizing Young Trees - UCANR

Fertilizing Young TreesPhoebe Gordon, Ph.D.

Orchard Systems Advisor, Madera and Merced Counties

Goal in fertilizing young trees• Get good growth to enable

scaffold development• Avoid pitfalls of overfertilization

• Lanky, rapid, weak growth• Scorch trees due to rapid nitrate

uptake• Avoid young juvenile dieback in

pistachios; early frost damage in walnuts

• Avoid nutrient imbalances in soils with low CECs Photos: D. Doll

Phoebe Gordon, University of California Cooperative Extension

Rules for nutrient uptake• Trees take up nutrients at rates reflecting

demand• Demand = growth rate IN YOUNG TREES• in mature trees it’s primarily driven by

yield• mo’ nutrients, mo’ growth? • (The answer is no.)

• Other tree needs need to be non-limiting to get a growth response from a specific nutrient

• Photosynthetic rate will eventually become limiting factor


Rules for nutrient uptake

• Trees won’t take up nutrients at a faster rate if more is in the soil• Trees do not take up nutrients during dormancy• Roots must be in good condition for nutrient uptake to occur• Roots in overirrigated, flooded, or compacted soils may not get

enough oxygen • Oxygen is essential for energy generation, which is essential for

nutrient uptake• Chronically dry soils can also reduce nutrient uptake!


What nutrients should you worry about?

• Nitrogen• Zinc• Phosphorus?• Potassium, boron more important when trees are bearing,

• Run the risk of inducing magnesium deficiency if trying to ‘load up’ lighter textured soils with potassium before they start bearing


Nitrogen

• Nitrogen is the most important macronutrient young trees will need

• Deficient in all production systems

• The amount that trees need is not necessarily the amount you will apply!

• Lbs residual N/acre = ppm NO3−N ∗2 ∗𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑 𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠 𝑠𝑠𝑠𝑠𝑠𝑠𝑑𝑑𝑠𝑠𝑑𝑑𝑑𝑑 (𝑠𝑠𝑖𝑖)

6 (𝑠𝑠𝑖𝑖)

• Lbs N in irrigation water = • Acre-inch: ppm NO3-N * 0.23

ppm NO3 * 0.052• Acre-foot: ppm NO3-N * 2.72

ppm NO3 * 0.62


Nitrogen

• Nitrate (NO3-) is highly mobile, and no matter what form of N you add, it all ends up as nitrate

• Application efficiency is highest when applications are split over the year

• In young orchards, application efficiency is highest when the nitrogen lands in the root zone

• Late applications of N can delay dormancy, which increases early winter frost damage risk

• Juvenile dieback in pistachios• Early frost damage in walnuts

• Late applications of N are also at a very high risk for leachingPhoebe Gordon, University of California Cooperative Extension

A young tree has a very limited root system…


Roots will expand quickly, but it will take time to fully exploit the wetted zone


Young tree fertilization trial – conducted by David Doll

• David Doll applied different rates (next slide) and sources of N fertilizer to young almond trees

• The source of N did not matter• D. Doll did not look at organic N,

but release rate is much slower. The lower the %N, the slower the release rate

• Maximum growth rate at approximately 3-4 oz N per treeImage source: Young Orchard Handbook,

http://ccfruitandnuts.ucanr.edu/files/238596.pdfPhoebe Gordon, University of California Cooperative Extension

http://ccfruitandnuts.ucanr.edu/files/238596.pdf

Zinc

• Zinc is required for synthesis of auxins; deficiencies can severely reduce growth

• Symptoms can resemble glyphosate drift

• Foliar spray is the best corrective, absorption is best in the early part of the season

• Many products available; follow label directions to avoid defolation Photo: Harry Andris, Fresno County


Phosphorus

• Little evidence that phosphorus deficiency is an issue in mature California orchards

• Tree P needs are very low (We think they need 5 ppm in the soil via Olsen Bicarb test)

• Plus most research on phosphorus fertilization has only shown positive results in soils low in available P

• Volcanic soils in California• Lateritic (highly weathered tropical soils) in Australia

• HOWEVER previous research, as well as a trial I conducted last year, shows some benefit from giving young trees P


Young tree fertilization trial – P. Gordon, G. Browne, N. Ott, A. Khan

• Conducted in unfumigated soil• The previous orchard was recycled and

incorporated• The control consisted of the grower’s

fertilization practice, which was to apply 10.5 lbs N/acre (UN32) via fertigation, and 0.25 lbs of N, 0.6 lbs of P, and 1.2 lbs of K over two foliar applications

• Fertilizer was hand-applied on each side of the tree, split up over 6 months

• Micro and slow release treatments were not split up over time

• Measured tree circumference at the end of the first growing season

Fertilizer treatments

Amount per application

Total amount applied

Control None N/A

15-15-156.66 oz, 5 applications

5 oz N, 5 oz P2O5, 5 oz K2O

Slow release 15-9-12+micros

40 oz, one application

6 oz N, 3.6 P2O5, 4.8 oz K2O

Phosphorus 0-46-0

2.17 oz, 5 applications 5 oz P2O5

Urea 46-0-02.17 oz, 5 applications 5 oz N

Micros2.7 oz, one application micro blend


Young tree fertilization trial – P. Gordon, G. Browne, N. Ott, A. Khan

-2

3

8

13

18

Phosphorus Slow Release 15-15-15 Nitrogen (urea) Micros Control

Trun

k Ci

rcum

fere

nce

(cm

)

Treatment

Fertilizer Trial October Trunk Circumference

BBAAAA


Young tree fertilization trial – P. Gordon, G. Browne, N. Ott, A. Khan• Nitrogen, phosphorus were

beneficial, however there was no synergistic effect

• The addition of potassium (included in two complete fertilizers) provided no growth effect

• Phosphorus uptake in trees depends on their extensive root systems; young trees do not have extensive root systems!

Terrible photography by Phoebe GordonPhoebe Gordon, University of California Cooperative Extension

Strategies for fertilizing young trees

• Any fertilizer that does not land in the immediate root zone in 1st leaf trees will not be utilized

• Nitrogen is easily wasted, especially in sandy soils in areas with decent winter rainfall

• Anything that ensures N stays in the root zone increases application efficiency

• Roots expand rapidly; less important in 2nd leaf trees and beyond

• Apply fertilizers by hand to the base of the tree

• Applying N via fertigation risks burning 1st leaf trees

• Incorporate slow-release fertilizers into the soil

• Incorporating them into the soil at planting for fall or winter plantings is likely too soon!


Timing

• Immobile nutrients (K, P) can be incorporated early in the season

• In non-WOR orchards, apply N once you see several inches of new growth

• In WOR orchards, apply N as soon as early as March

• Keep rain in mind; if you are hand applying fertilizer, do not apply in advance of heavy rain

• Do not fertilize late into the season to encourage transition into dormancy

• Stop fertilizing walnuts after August

• Stop fertilizing pistachios after early July

• Early frost damage has not been a concern in almonds


Suggested young almond nitrogen rates

Age Rate per acre Rate per tree

1st leaf 20-25 3-4

1st leaf with WOR?

40-50 3-8

2nd leaf 20-25 + 68 lbsN/1000 lbs yield

3-4

3rd leaf on 25-30 + 68 lbsN/1000 lbs yield

N/A

• Almonds grown in sites with recycled orchards may need twice the amount of nitrogen in the first year only

• However early applications(March) may reduce tree nitrogen needs; we suggest staying closer to 3 oz and applying more as needed

• Apply no more than one ounce of actual nitrogen a monthSpacing assumes 120 trees per acre


Suggested young walnut nitrogen needs

• Walnut N needs have not been evaluated experimentally, suggested rates are based on high vigor of young walnuts

• Excessive N applied late in the season can delay dormancy and increase the risk of damage from early frost

Assumes 65 trees/acre


1st leaf 12 – 16 lbs N 3-4 oz N

2nd leaf 24 – 32 lbs N 6-8 oz N

3rd leaf 24 – 32 lbs N 6-8 oz N

4th leaf 24 – 32 lbs N + 36 lbs N/ton nuts

6-8 oz N


Suggested young pistachio nitrogen needs

• Pistachio N needs have not been evaluated in young trees experimentally, suggested rates from Craig Kallsen

• Excessive or late N applications increase the risk from juvenile winter dieback (cold damage)

• Applications in year 5 and beyond assume trees are bearing small amounts of nuts, reduce if no crop present

Assumes 120 trees/acre


0 (pre budded) 10 1 1/3 oz

1 15 2 oz

2 20 2 2/3 oz

3 30 4 oz

4 40 5 1/3 oz

5 55 7 1/3 oz

6 75 10 oz

7 135 + 28 lbs1000 lbs yield

18 oz


Potassium?

• Unlike nitrogen, potassium is immobile in soils and most soils can supply enough for low demands

• Like nitrogen, fruit demand the vast majority of K uptake in bearing trees

• Soil test: %K in CEC >2% or over 200 ppm is likely fine

• Vegetative K2O needs in mature pistachios: 26 lbs/acre

• Vegetative K2O needs in mature almonds, walnuts, not officially determined, but is likely not much different from nitrogen

• Heavy applications in light textured soils can result in cation imbalances


Why can cation imbalances occur?

• Cations are held in soil by the Cation Exchange Capacity

• In soils with a low CEC, heavy additions of one cation (potassium, sodium) can force off other cations (calcium, magnesium)

• Maintaining strict ratios for ideal growth rates has not been supported by science

• But you can create problems with heavy additions in soils that can’t handle it


Magnesium deficiency

• Shows up in older leaves• Mobile in plants, will be taken

from older leaves and put into new leaves

• Magnesium sulfate can rectify this, as well as dolomitic limestone in acidic soils


Leaf sampling

• Leaf critical values are based on bearing trees,

• N, K is exported to fruit, will be higher in non-bearing trees

• Ca, Mg, B (walnuts and pistachios) may be much lower

• Leaves that emerge at bud break have several months to build up these nutrients; MRM leaves may have only been expanded for a month before sampling!

• No leaf tissue suggestions for almonds, walnuts

• Pistachios: leaf values of 2.6-2.9% N should be sufficient for rapidly growing trees


Fertilizing Young Trees - UCANR

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