Citrus
Citrus fruits, comprising six different genera, are important economic fruits and represent the highest-value fruits in terms of international trade. There are two main markets for citrus fruit. Citrus is produced for the fresh fruit market and the processed citrus fruits market (mainly orange juice).
Citrus - crop with high potassium requirements for optimal growth, yield, and quality
- Citrus fruits are nutritious fruits and are popular for their taste and high vitamin C content
- Citrus trees are native to tropical and subtropical regions
- The trees have a high demand for potassium, which is needed for numerous physiological functions and is responsible for high yield and quality
- Citrus plants require magnesium and sulfur in particular to meet peak demand during fruiting. An adequate supply of these two nutrients is essential for good yield and, above all, high quality
- For ensuring the full spectrum of nutrients, including micro nutrients, foliar applications with soluble micronutrient fertilizers based on EpsoTop with magnesium sulfate as carrier are recommended
Citrus – rich in vitamins
The citrus fruits, comprising the species oranges, mandarins, grapefruits, and lemons, are currently 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, followed by China and the USA. The latter is number one producer of grapefruits, whereas Brazil is leading the production of oranges, and China the production of tangerines. Spain and Italy are also important producers of oranges and tangerines, whereas India is the leader in lemon and limes production.
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 applications.
The most important nutrients for Citrus
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.
Magnesium and sulfur – covering peak demand at fruit formation and growth control
- 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, starch, and proteins, which are essential to fruit yield and quality.
- Magnesium is required for an appealing skin color 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.
Sulfur – for growth control
- Sulfur is a constituent of amino acids (methionine and cystine) and therefore it is needed for the formation of proteins and chlorophyll.
- Sulfur has an important impact on the photosynthesis rate as an optimal photosynthesis rate is necessary to obtain high yields.
Micronutrients – securing 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.
- 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.
|
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
Fertilizer 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 fertilizer rates accordingly. A general guideline is given in the table below where the recommendation is based on tree age.
Recommendation for soil fertilization
|
Age 1 : 350-450 K (g tree-1) 700-900 Sop (g tree-1) 35-105 Mg (g tree-1) |
|
|
Age 2-3 : 600-750 K (g tree-1) 1200-1500 Sop (g tree-1) 60-160 Mg (g tree-1) |
|
|
Age 4-6 : 800-1200 K (g tree-1) 1600-2400 Sop (g tree-1) 80-260 Mg (g tree-1) |
|
|
Age 7-8 : 1000-1500 K (g tree-1) 2000-3000 Sop (g tree-1) 105-290 Mg (g tree-1) |
|
|
Age >8 : 1200-1800 K (g tree-1) 2400-3600 Sop (g tree-1) 120-320 Mg (g tree-1) |
|
Recommendation for foliar fertilization
epsoMICROTOP and epsoCOMBITOP are foliar fertilizers which can be used in citrus production to meet the manganese needs of citrus. The application is generally made during the time when the new shoots are fully developed.
