Mandarin Orchard Floor Management

Cindy Fake University of California Cooperative

Extension, Placer & Nevada CountiesApril 2012

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!

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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

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!

Orchard Floor Management Techniques• Mulch• Cover crops• Minimize cultivation - maintain

undisturbed root zone• Divide fertilizer

applications to optimize nutrient use

• Ensure good drainage

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

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

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!

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

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

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!

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

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

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.

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

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

No-till Citrus Orchard Management

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

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

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

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

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

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

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, orvertebrate pest damage

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

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

Mulch Materials: Manures

• Manures have slightly higher nutrients than plant compost aloneNutrient ranges for manures:

Poultry manure: up to 4.5% N, 6%P, 2.5%KGoat manure (dry): up to 2.7% N, 1.8%P, 2.8%KHorse manure: up to 3%N, 2%P, 3%KSheep manure: up to 6.0%N, 3.0%P, 2.50%KSteer manure: up to 2.5%N, 1.6%P, 3.6%K

Mulch Materials: Plant Residues

• Composted crop residues• Kitchen waste• Prunings• Straw• Wood shavings or chips • Sawdust is best composted with

manures

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

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.

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

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

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

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

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

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

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

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%

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

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

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.

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.

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.

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

Questions?

Thank you!