Citrus Nutrient Management

Cindy Fake University of California Cooperative

Extension, Placer & Nevada CountiesApril 2012

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!

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

Orchard Floor Management Techniques• Minimize cultivation - maintain

undisturbed root zone• Divide fertilizer

applications to optimize nutrient use

• Ensure good drainage

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

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.

Nutrient Management?

Thank you!

Cindy Fake University of California Cooperative

Extension, Placer & Nevada CountiesApril 2012