This document discusses nutrient management for citrus orchards. It emphasizes the importance of proper orchard floor management to provide a good root environment. Techniques like minimizing cultivation, using cover crops, and applying mulch are recommended. The benefits of soil organic matter for nutrient retention and tree health are covered. Guidelines are provided for soil testing and applying the proper amounts of nitrogen, phosphorus, potassium, and micronutrients based on soil conditions. Fertilizer sources and application timing are addressed. The importance of a balanced soil management program tailored to individual orchard needs is stressed.

1. Citrus
Nutrient Management
Cindy Fake
University of California Cooperative Extension,
Placer & Nevada Counties
April 2012

2. Importance of Orchard Floor Management
• Most roots in top 30 cm, under
tree canopy
• Small root zone to exploit
• Manage soil to provide good
root/soil environment
• Not just nutrient management,
but soil management
• Feed the soil to feed the tree!

3. Agenda
• Soil and tissue testing
• Benefits of soil organic matter
• No-till orchard management
• Cover crops and vegetated row middles
• Mulch
• Soil nutrient management
3

4. Orchard Floor Management Techniques
• Minimize cultivation - maintain undisturbed
root zone
• Divide fertilizer
applications to optimize
nutrient use
• Ensure good drainage

5. Soil Management
• Citrus grow well in slightly acid soils
• Below pH 5.5 - amend with lime or
dolomite to raise pH
• Organic matter additions may reduce
impacts of low pH
• Low fertility soils will need
amendments and/or fertilizer
• Soil management program should be
based on soil and leaf analysis

6. Mulch Materials: Manures
• Cow, horse, goat, or sheep
• Poultry manure should
be composted with plant
materials – too much N
• Best is partially composted
manure, excess salts and urea leached out
• Pile manure and allow to rot for
1-2 months, then apply to trees.
• Mix manure with bedding, straw, wood chips or other
plant materials and compost

7. Mulch Materials: Manures
• Manures have slightly higher nutrients
than plant compost alone
Nutrient ranges for manures:
Poultry manure: up to 4.5% N, 6%P, 2.5%K
Goat manure (dry): up to 2.7% N, 1.8%P, 2.8%K
Horse manure: up to 3%N, 2%P, 3%K
Sheep manure: up to 6.0%N, 3.0%P, 2.50%K
Steer manure: up to 2.5%N, 1.6%P, 3.6%K

8. Mulch Materials: Plant Residues
• Composted crop residues
• Kitchen waste
• Prunings
• Straw
• Wood shavings or chips
• Sawdust is best composted with
manures

9. Soil Nutrient Management
• Best citrus nutrient
management practices
combine compost,
composted manure and/or
cover crops with specific
fertilizer applications
• Increased organic matter
– keeps nutrients in the root zone
– makes fertilizer applications more effective
• Legume cover crops can contribute N

10. Soil Nutrient Applications
• Most orchards need annual applications of nitrogen
(N) and zinc (Zn)
• May need micronutrients such as manganese, boron,
or iron
• Phosphorus (P) may be needed in
acid soils
• Potassium (K) may also be needed
• Soil and tissue analysis should be
used to determine your orchard’s
needs.

11. Fertilizer Applications : Nitrogen
• N is important for citrus
• Often overapplied
• Excess N
– Affects fruit quality
– Contributes to susceptibility to frost
and insect damage
– Delays fruit maturity
• Important to match N from all
sources to actual tree needs

12. Timing of Nitrogen Applications
• Apply N in spring, from bloom through
fruit set, finish by July
• Do not start applications until winter
rains diminish
• N is mobile in the soil
• Citrus cannot take up N when soils are
cold and wet, so it is lost
• Make multiple N applications in small
amounts
• Apply N under the canopy and cover it
with mulch

13. Types of Nitrogen Fertilizers
• Nitrate forms of nitrogen should be
used on acid soils
• Ammonium (NH4
+) fertilizers acidify
the soil
• If only ammonium fertilizers are
available, always use in conjunction
with organic matter
• Liming may also be needed

14. Citrus Nitrogen Needs: New trees
• Divide into 4-6 applications from March through July
• Year 1: 50 g actual nitrogen per tree
• Year 2: 100 g actual N per tree
• Year 3: 100-200 g depending on size
• Year 4: 250 g per tree

15. Citrus Nitrogen Needs: Mature trees
• Mature citrus need 250-500 g actual N/tree/year
• Big trees with large canopies = 500 g
• Smaller mature trees ~250 g
• Multiply %N in the material by the weight to get
actual N. e.g.
– Ammonium nitrate (34.4-0-0)
has 34.4% N(.344 x 50 = 17.2)
– 50 kg bag has ~17.2 kg actual N
– So, a 50 kg bag will feed about
35 large mature trees or 69
smaller mature trees with N

16. Citrus Nitrogen Needs: Mature trees
• Label lists % by weight of N-P-K
• % Nitrogen
• % P expressed as P2O5
• % K expressed as K2O
• 15-15-15 has 15% N, 15% P2O5,
and 15% K2O
• Nitrogen calculation: Multiply %N in the material by
the weight to get actual amount of N
• A 50 kg bag (.15 x 50 =7.5) has 7.5 kg actual N
• So, a 50 kg bag will feed about 30 mature trees with
250 g N per tree

17. Citrus Nitrogen Needs: Mature trees
• P is expressed as P2O5, which is only 43%P
• Calculation for P:
• 50 kg bag 15-15-15 has 7.5 kg P2O5 (.15 x 50 =7.5),
but P2O5 is only 43% p, so actual P is 7.5 kg x .43 =
3.2 kg P in bag
• K is expressed as K2O, which is 83% K
• Calculation for K:
• 50 kg bag 15-15-15 has 7.5 kg K2O (.15 x 50 =7.5),
but K2O is only 83% p, so actual K is 7.5 kg x .83 =
6.2 kg K in bag

18. Nitrogen Sources
• Synthetic N has become more expensive
so growers rely on cover crops, manures,
and composts
• Legume cover crops can fix 35-75
pounds of N per acre in mixed stand
• Compost nutrient content is dependent on
the feedstock
• Poultry manure contains the most N, on
average about 4%

19. Phosphorus Fertilizers
• Acidic soils may contain enough phosphorus (P), but
it may not always be available to plants
• P fertilizer should not be applied unless a soil test
indicates need
• Excess P can contaminate surface and groundwater
• P deficient trees produce more fruit with thick rinds
and less juice,
reducing marketable yield

20. Potassium
• Potassium may be leached out of
acid sandy soils, causing
deficiency, but in clay soils it is not
usually a problem
• Potassium helps maintain rind
integrity and improves sugar/acid
balance and flavor in fruit
• Foliar applications as fruit mature
may lengthen shelf life and
increase sugar content

21. Micronutrients
• Zinc (Zn) and manganese (Mn)
– Springtime foliar sprays at rates of 500 to 1,000
mg/L of Zn and 300 to 700 mg/L of Mn
• Iron is sometimes needed, especially in
areas with drainage issues
• Boron (B) should only be applied if soil and
tissue tests indicate a need. The range is
very narrow, and excess B can damage trees.

22. Nutrient Applications
• Some nutrient applications may be needed for optimal
production
• Soil depth, nutrient, and organic matter content vary
greatly
• Rootstock and soil conditions also influence nutrient
uptake
• Any fertilizer program
should be based on soil and
tissue sampling, not on a
standard recommendation.

23. Good Soil Management Practices
• A healthy, productive citrus tree needs a
healthy soil environment
• Good soil management
– Minimizes root disturbance
– Builds and maintains soil organic matter
– Provides adequate nutrients to the trees
• Feeding the soil to feed the plant results
in vigorous, productive citrus trees.

24. Nutrient Management?
Thank you!
Cindy Fake
University of California Cooperative Extension,
Placer & Nevada Counties
April 2012