Quick reference guide to mineral nutrients for citrus production

Released/reviewed: Sep 2009

Nitrogen (N)

Symptoms of nitrogen deficiency
Symptoms of nitrogen deficiency include pale green foliage, yellowing of older leaves & twig dieback.
Photo: R G Weir & G C Cresswell 1993, Plant Nutrient Disorders 1: Temperate and Subtropical Fruit and Nut Crops.

An excess of nitrogen
An excess of nitrogen or potassium can result in thick-skinned fruit with rough rinds.
Role in plant Vital part of proteins & chlorophyll. Proteins are involved in metabolism & chlorophyll is involved in making sugar using carbon dioxide from the atmosphere & sunlight.
Symptoms of deficiency Poor stunted shoot growth, old leaves pale green-yellow, thin foliage cover & dieback of twigs. Poor fruit set & fruit size. Fruit quality good.
Symptoms of excess Vigorous vegetative growth. Thick-skinned large, puffy fruit, delayed maturity, regreening likely. Juice % & quality declines. Shorter storage life.
Movement in soil Mobile
Movement in plant Mobile
Availability to tree roots Nitrate form preferred, but ammonium also taken up. Conversion between these forms dependent on soil temperature, organic matter & microbial activity, which is greatest in pH range of 5.5-8.5. Use readily available form (i.e. nitrate) during cooler months.
pH effects on availability to tree roots None known
Interactions with other elements Higher tree N levels (>2.6% in leaves) associated with lower boron &/or sulfur in leaves. Effect of excessive N worsened by low P supply.
Other information Easily leached in sandy soils. Lost to atmosphere in waterlogged soils.



Phosphorus (P)

Role in plant Metabolism, cell division & growth.
Symptoms of deficiency Old leaves dull bronzed green. Fewer flowers. Misshapen fruit, open centres, thick coarse peels. Pulpy fruit, lower juice, more acid.
Symptoms of excess Smaller fruit, higher % juice thinner peels, chance of regreening.
Movement in soil Immobile
Movement in plant Mobile
Availability to tree roots Available & unavailable forms present; relative proportions dependent on soil pH. In alkaline soils P fixed in calcium compounds, & iron & aluminium compounds in acid soils. Unavailable forms act as a reserve for available forms. Most P in upper soil layer. Australian soils naturally low.
pH effects on availability to tree roots Most available in range 67.
Interactions with other elements Too much P can accentuate the effects of low zinc availability, induce iron deficiency and affect copper uptake.
Other information Losses from soil only in erosion of soil particles or in very sandy soils. Soil compaction reduces uptake.

Potassium (K)

Role in plant Metabolism, water relations, internal balance, stress & disease resistance.
Symptoms of deficiency Slower growth, small leaves, and heavy leaf fall. Severe deficiency causes heavy flower/fruit drop. Small, smooth thin-skinned fruit that colour early, split easily & are more prone to albedo break-down.
Symptoms of excess Thicker rough rinds & chance of regreening. Delayed maturity in oranges.
Movement in soil Mobile
Movement in plant Mobile
Availability to tree roots Soils contain large amounts but most is unavailable.
pH effects on availability to tree roots None known
Interactions with other elements Excessive K supply reduces magnesium & calcium uptake.
Other information Large amounts removed in fruit.

Sulfur (S)

Role in plant As for N, but required in much lesser amounts.
Symptoms of deficiency Younger leaves stunted, pale green-yellow with lighter veins.
Symptoms of excess None known
Movement in soil Mobile
Movement in plant Mobile
Availability to tree roots Available to plants only in sulfate form. Most soil sulfur present in the organic matter.
pH effects on availability to tree roots Less available in low pH soils.
Interactions with other elements None known
Other information Sulfate forms easily leached. Long-term use of ammonium sulfate leads to lower soil pH.

Calcium (Ca)

Role in plant Metabolism, internal balance, tissue strength.
Symptoms of deficiency Stunted roots, higher incidence of albedo breakdown.
Symptoms of excess None known
Movement in soil Immobile
Movement in plant Immobile
Availability to tree roots Plant available Ca associated with soil cation exchange capacity. High Ca levels in high pH soils due to calcium carbonate (lime).
pH effects on availability to tree roots Deficient in low pH (acid) soils.
Interactions with other elements Heavy applications of K may reduce Ca uptake. Deficiencies, more likely on acid soils. Calcium carbonate can reduce iron uptake ("lime-induced iron chlorosis").
Other information Other important sources of Ca include gypsum (calcium sulphate) & single strength superphosphate.

Magnesium (Mg)

Magnesium deficiency
Magnesium deficiency shows up in older leaves first.

Magnesium deficiency
Photo: R G Weir & G C Cresswell 1993,
Plant Nutrient Disorders 1: Temperate and Subtropical Fruit and Nut Crops.
Role in plant Synthesis and function of chlorophyll & protein, internal balance.
Symptoms of deficiency Yellowing towards apex of leaves with a triangular area remaining green at base in older leaves, defoliation and shoot dieback. Smaller fruit and lower yield.
Symptoms of excess None known
Movement in soil Attaches to clay particles.
Movement in plant Mobile
Availability to tree roots Plant available Mg associated with soil cation exchange capacity.
pH effects on availability to tree roots Lower in sandy, acid soils.
Interactions with other elements Heavy applications of potassium reduces Mg uptake.
Other information Important in cation exchange.







Zinc (Zn)

Zinc
Zinc deficiency shows up in young leaves first.
Role in plant Chlorophyll formation, protein synthesis, phytohormone metabolism; stress tolerance.
Symptoms of deficiency Leaves generally small & narrow, creamy white to yellow blotches on young leaves. Retarded terminal growth, small twigs die, tree vigour reduced. Lowers yield of small poor quality fruit.
Symptoms of excess None known
Movement in soil Mobile in acid soils.
Movement in plant Immobile
Availability to tree roots Availability reduced by high levels of organic matter, over-liming and overuse of poultry manure. More available when soil temperatures are warm.
pH effects on availability to tree roots Less available above pH 6.0.
Interactions with other elements High phosphorous can induce zinc deficiency by reducing both uptake by roots & use within the tree.
Other information Nitrogen materials favour zinc availability. Symptoms more pronounced on north side (sunny) of tree.

Copper (Cu)

Role in plant Tissue strength, stress tolerance, carbohydrate metabolism.
Symptoms of deficiency Dark brown gum pockets on young shoots & shoot dieback. Peel may be brown, with gum stained areas. Fruit splitting more likely.
Symptoms of excess Stunted roots & shoots.
Movement in soil Mobile in acid soils.
Movement in plant Immobile
Availability to tree roots Dependent on pH, organic matter content, presence of aluminium, molybdenum & iron.
pH effects on availability to tree roots Progressively less unavailable as pH rises above 7.0.
Interactions with other elements Excess may induce iron deficiency.
Other information Availability can be reduced by increasing soil organic matter.

Manganese (Mn)

Manganese
Manganese deficiency shows up in young leaves first.

Manganese
Manganese toxicity symptoms include yellowing on margins of old leaves & dark brown tar spots. Photo: R G Weir & G C Cresswell 1993, Plant Nutrient Disorders 1: Temperate and Subtropical Fruit and Nut Crops.
Role in plant Chlorophyll & protein function, stress tolerance, cell elongation.
Symptoms of deficiency Young leaves mottled pale green, interveinal yellowing, reduced growth & slight loss in yield.
Symptoms of excess Bright yellowing on margins of old leaves, dark brown tar spots on leaves.
Movement in soil Mobile in acid & waterlogged soils.
Movement in plant Immobile
Availability to tree roots More available in waterlogged conditions; excessively available in acid (pH<4.3) soils potentially leading to toxicity.
pH effects on availability to tree roots Becomes less unavailable as pH rises above 5.5.
Interactions with other elements High levels can induce iron deficiency. Manganese deficiency more acute when nitrogen levels low.
Other information Symptoms more noticeable on southern side of tree.








Iron (Fe)

Iron
Iron deficiency shows up on young leaves first.
Role in plant Chlorophyll synthesis & nitrogen metabolism.
Symptoms of deficiency Young leaves chlorotic, stunted abnormal growth, tips/margins/veins stay green longest. Lower vigour. Reduced yield.
Symptoms of excess No known symptoms.
Movement in soil Mobile in waterlogged soils.
Movement in plant Immobile
Availability to tree roots In very acid soils, phosphates can be tied up by soluble iron & aluminium. High water table & water logged conditions aggravate problem.
pH effects on availability to tree roots Becomes less available as pH rises above 7.0
Interactions with other elements High iron levels can induce a manganese deficiency. Fixes phosphorous.
Other information Symptoms more noticeable on southern side of tree.

Boron (B)

Boron
Boron deficiency symptoms can include pockets of brown gum in the pith of fruit.
Photo: R G Weir & G C Cresswell 1993,
Plant Nutrient Disorders 1: Temperate and Subtropical Fruit and Nut Crops.
Role in plant Pollen tube growth, cell elongation, tissue strength, phytohormone metabolism.
Symptoms of deficiency Stumpy roots, yellow veins on young leaves. Lopsided malformed grey to brown fruit with gum pockets. Heavy fruit shedding.
Symptoms of excess Yellow, dead leaf tips, leaf fall & dieback. Reduced yield.
Movement in soil Mobile
Movement in plant Immobile
Availability to tree roots Available forms found in soil solution. Dry periods & over liming can induce a deficiency.
pH effects on availability to tree roots None known
Interactions with other elements Calcium renders boron insoluble therefore used to overcome an excess.
Other information Narrow range between deficiency & toxicity. Easily leached.

Molybdenum (Mo)

Role in plant Nitrogen metabolism
Symptoms of deficiency Symptoms similar to nitrogen deficiency although tissue tests may indicate sufficient N; yellow spots on leaves in spring.
Symptoms of excess No known symptoms.
Movement in soil Immobile
Movement in plant Mobile
Availability to tree roots Deficient in acid soils which contain iron or aluminium oxides.
pH effects on availability to tree roots Decreases below pH 6.
Interactions with other elements None known

Aluminium (Al)

Role in plant None
Symptoms of deficiency No known symptoms.
Symptoms of excess Stunted root growth. Lack of root hairs.
Movement in soil Immobile
Movement in plant None
Availability to tree roots Toxicity highly likely in soils below pH 4.3.
pH effects on availability to tree roots Availability decreases above pH 5.5.
Interactions with other elements Fixes phosphorus in acid soils.

Sodium (Na)

Role in plant Internal balance
Symptoms of deficiency No known symptoms.
Symptoms of excess Leaf burn, defoliation & dieback.
Movement in soil Mobile
Movement in plant Mobile
Availability to tree roots Uptake more likely in waterlogged soils, on some rootstocks & with saline irrigation water.
pH effects on availability to tree roots None known
Interactions with other elements Sodium ions displaced by calcium.
Other information Buildup in soil leads to sodic soils.

 

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