This document provides guidance on orchard floor management techniques for mandarin orchards. It discusses the importance of proper soil and nutrient management for citrus trees, which have shallow root systems. Key recommendations include using no-till practices to protect roots, improving drainage in wet soils, adding organic matter through cover crops, mulches and compost, and dividing fertilizer applications based on soil and tissue tests. Maintaining undisturbed soil with adequate organic matter through these techniques helps promote healthy root growth and maximize fruit yields.

1. Mandarin Orchard Floor
Management
Cindy Fake
University of California Cooperative Extension,
Placer & Nevada Counties
April 2012

2. Importance of Orchard Floor Management
• Citrus have shallow roots, most
in top 30 cm of soil
• 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
• Orchard floor techniques
• Mandarin root structure
• Improving drainage
• Mandarin soil management
• 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. Importance of Orchard Floor Management
• Citrus have shallow roots, most
in top 30 cm of soil
• 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!

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

6. Mandarin Root Structure
• Typically no tap root
• Woody lateral roots radiating
from the trunk
• Fibrous feeder roots grow from
woody roots
• Feeder roots absorb nutrients and
water
• Most roots in top 30 cm, under tree
canopy
• 3 root growth flushes: early spring,
early summer and late summer

7. Mandarin Roots in Saturated Soil
• Citrus root growth starts ±12ºC
• Roots do not function in saturated (very wet) soil
• Citrus roots need oxygen and water
• In wet soil, tree roots cannot “breathe”
• Absorbing roots start to die
within 1 to 2 weeks
• Major root loss =>
yellowing leaves, then leaf drop
• Worse in hot weather

8. In Chronically Saturated Soils…
• Fibrous roots grow on the soil surface
• Not enough oxygen is
available in the soil
• Roots have plenty of water,
but cannot get nutrients
from soil
• These roots should not be
removed, they may be the ONLY functioning roots
• Improve drainage!

9. Improving Drainage
• Dig shallow drainage ditches
across the slope for runoff
• 1-2º downward slope
• 15 m intervals in heavy clay soil
• 30-60 cm deep, V shaped
• Top width 2+ m
• Bottom 1-1.5 m
Use A-frame level
to determine slope

10. Improving Drainage
• Protect drainage ditches with gravel or stones to
prevent erosion
• Allow vegetation to grow in ditches
to slow runoff
• Or install drainage pipe

11. Other problems with Saturated Soil…
• Increases Phytophthora root disease
• Disease damages roots, decreases
productivity
• Toxic levels of gases e.g. hydrogen
sulfide (H2S) collect in wet soil
• Improving drainage in heavy soils
=> improve tree health & root mass
=> increased yields & fruit quality
Goal is healthy roots
for a healthy tree!

12. Mandarin 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

13. Soil and Tissue Testing
• Plan your nutrient program
from soil and tissue analysis
• Have soil analyzed each year
for 2+ years after planting
• For older trees, analyze
every 4-5 years
• Test soil before major
fertilizer or amendment
applications

14. Taking Soil Samples
• Take 8-10 soil samples throughout the orchard
• If the soil is uniform, combine samples into one
• If the soil or vegetation looks different, sample that
soil separately
• Clear vegetation and debris from soil surface
• Dig a 15-20 cm hole and mix the soil in the hole
• Scoop out a cupful of soil and place in plastic bucket.
• Mix samples well, use one cupful for lab sample
• Place sample in an open paper bag to air dry.
• Label bag with field location and date of sampling.

15. Benefits of Soil Organic Matter
• Soil organic matter = compost, manure, mulch,
and/or cover crops
• Slow nutrient (N, P, S) release
• Improves drainage in clay soils
• Beneficial microbes =>
healthy roots
– Concentrate nutrients in the root zone
– Predators of disease-causing
microbes and nematodes
• Increase effectiveness of fertilizers
• Moderates high & low temperatures, reduces stress

16. No-till Orchard Management
• Soil under mandarin trees should
not be cultivated
• No disking or cultivation of
citrus orchards
• No-till protects roots and beneficial
soil microbes
• Prevents root damage which can lead to disease
• Slows the decomposition of organic matter
• The best orchard floor is undisturbed soil covered
with organic matter, such as cover crops, mulch, or
compost

17. No-till Citrus Orchard Management

18. Ways to Increase Soil Organic Matter
• Organic matter decomposes rapidly in warm
climates, especially with high humidity
• Annual applications needed
• Preserve native cover: mow weeds and leave residue
on surface under tree canopy
• Overseed native cover with
legumes to increase N
• Plant cover crops
• Apply compost, manure, or
wood chips as mulch around
trees

19. Benefits of Cover Crops
and Vegetated Row Middles…
• Increase soil organic matter
• Improve soil structure and
drainage
• Help drain saturated soils
• Improve nutrient holding
capacity: N, P, S
• Improve water penetration
• Reduce runoff and soil erosion

20. Cover Crops and Vegetated Row Middles…
• Allow tree roots to remain
active closer to the soil surface
• Increase beneficial microbes
• Habitat for beneficial insects
• Moderate summer soil
temperatures, reducing
tree stress

21. Cover Crops
• Cover crops are planted to feed the
soil, not be harvested as a crop
• Grasses: oats, rye, or fescue = slow
organic matter
• Legumes: clovers or vetch;
fix N
• Provide nutrients and organic
matter
• May choke out invasive weeds

22. Cover Crops
• Provide permanent organic matter
from grasses
• Provide inexpensive source of N
with legumes
• Legume = ⅓ to ½ of mix, provides
35-75 kg N/ha
Crimson clover, cereal rye, and hairy vetch

23. Planting Cover Crops
• Plant in fall
• Germinate before cold
weather
• Provide soil cover over
winter - prevents erosion
• Mowed in spring to mulch orchard floor
• Once planted, becomes a permanent crop
• May need to be overseeded from time to time

24. Mulch
• Enhances root zone under tree canopy
• Provides organic matter to the soil
• Materials include manures, compost, wood chips,
straw, shredded prunings
• Readily available, low cost
materials without contaminants
• Place 10 cm out, around trunk
• Mulch out to tree’s drip line
• Do not pile mulch against trunk;
Potential for fungi, insect, or
vertebrate pest damage

25. Mulch Application
• In larger orchards, mulch applied from a spreader
• 50-100 cm-wide band along tree row
• 10-20 cm out from the trunk, depending on canopy
• Depending on moisture content,
10 to 40 tons/hectare annually
• Higher amount needed
if no previous organic
matter applications
• Decrease amounts in
succeeding years

26. 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

27. 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

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

29. 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

30. 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.

31. 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

32. 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

33. 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

34. 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

35. 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

36. 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

37. 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

38. 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%

39. 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

40. 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

41. 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.

42. 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.

43. 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.

44. Good Agricultural Practices (GAPs)
may increase yields…
• But, growers must weigh the cost of the practices
against the increased revenue from higher quality or
higher yields
• Practice must provide an
increased return to
compensate for the
increased production cost

45. Questions?
Thank you!