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Citrus

Citrus – rich in vitamins

Potassium – for optimal yield and quality

Magnesium – to cover peak demand at fruit formation

Sulphur – the growth control

Micronutrients – to secure yields and quality

Fertiliser recommendations

 

Citrus – rich in vitamins

The citrus fruits, comprising the species oranges, mandarins, grapefruits and lemons, are currently collectively the most important group in terms of production worldwide. Citrus fruit is grown mainly in tropical and subtropical regions of the world. Today, Brazil is the largest producer of oranges and Japan of mandarins. Spain, Italy and Mexico lead in the production of lemon and limes, while the USA produce the largest quantity of grapefruit.

 
Citrus fruits are rich in vitamins, especially vitamin C. Its mild acid and bitter taste is good for the digestion and blood circulation. Citrus fruits are either consumed fresh or processed. The citrus peel is rich in pectin which is used in the production of jellies, marmalades, sweets, jams and pharmaceutical preparations.

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Potassium – for optimal yield and quality

Citrus crops have a high demand for potassium. The potassium requirement in high-yielding fruit orchards often equals or even exceeds that of nitrogen.

  • potassium plays an important role in most metabolic processes, e.g. photosynthesis and is essential for osmotic turgor regulation, protein and carbohydrate synthesis, translocation of assimilates (sugar and starch) and enzyme activation
  • potassium is needed for the development of a good root system and promotes general tree growth
  • adequate potassium supply improves the plants resistance to diseases and adverse weather conditions, particularly drought and cold
  • potassium improves fruit number and size as well as quality parameters, such as the acidity of the fruit juice and the vitamin C content 

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Magnesium – to cover peak demand at fruit formation

  • magnesium is the central atom of the chlorophyll molecule and traps the light energy during photosynthesis and converts it into sugar
  • an improved photosynthesis improves the production rate of sugars, starches and proteins, which are essential to fruit yield and quality
  • magnesium is required for an appealing skin colour and ensures an optimal content of soluble solids, acidity and vitamin C
  • magnesium promotes the drought and cold tolerance of citrus trees, reducing frost damage significantly

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Sulphur – the growth control

  • sulphur is a constituent of amino acids (methionine and cystine) and therefore it is needed for the formation of proteins and chlorophyll
  • sulphur has an important impact on the photosynthesis rate as an optimal photosynthesis rate is necessary to obtain high yields

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Micronutrients – to secure yields and quality

In citrus, a wide range of deficiencies may occur, so that it is advisable to evaluate the crop’s nutritional requirements locally, especially with regard to micronutrients, as their impact on yield and quality is often underestimated.

 

Threshold levels of micronutrient concentrations in 4-6 month old spring cycles leaves from non-fruiting terminals

 

Range
mg kg-1 in dry matter
 
Fe Mn Zn Cu B Mo
Deficient
<35
<17
<17
<3
<20
<0.05
Low
36 - 59
18 - 24
18 - 24
3 - 4
21 - 35
0,06 - 0,09
Optimum
60 - 120
25 - 100
25 - 100
5 - 16
36 - 100
0,10 - 1,0
High
121 - 200
101 - 300
101 - 300
17 - 20
101 - 200
2,0 - 5,0
Excess
>200
>500
>500
>20
>250
>5,0

 

Sources: Smith, 1966; Koo, 1984: Malavolta, 1989

 

  • Manganese is very important for the photosynthesis, root growth, sugar production and the disease resistance
  • Zinc deficiency causes stunted trees; leaf and stem size is reduced
  • Iron is needed in enzyme systems and in the electron transport during photosynthesis

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Fertiliser recommendations

The quantity of nutrients needed to adequately supply the requirement of productive citrus orchards depends on species, variety, soil, climate and yield expectation. It is recommended to take soil samples during planting and repeat at regular 3 - 5 year intervals. Annual leaf analysis is a suitable tool to determine the nutritional status and adjust the fertiliser rates accordingly. A general guideline is given in the table below where the recommendation is based on tree age.

 

Age (years)
K
(g tree-1)
Sop
(g tree-1)
Mg
(g tree-1)
ESTA Kieserita
(g tree-1)
Patentkali
(g tree-1) *
1
350 - 450
700 - 900
35 - 105
200 - 600
120 - 1500
2 - 3
600 - 750
1200 - 1500
60 - 160
350 - 900
2000 - 2500
4 - 6
800 - 1200
1600 - 2400
80 - 260
450 - 1500
2700 - 4000
7 - 8
1000 - 1500
2000 - 3000
105 - 290
600 - 1800
3300 - 5000
> 8
1200 - 1800
2400 - 3600
120 - 320
750 - 2000
4000 - 6000

 

* The preferred application to replace SOP and Kieserite application where Patentkali is available in the market.

 

Micronutrients can be applied through both soil and foliar application although the latter is usually recommended, especially for the alleviation of acute deficiency or as a means of tree health insurance.

 

EPSO Microtop and EPSO Combitop are foliar fertilisers which can be used in citrus production to satisfy the manganese needs of citrus. The application is generally made during the time when the new shoots are fully developed.

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