Author: Mr. Arik Kaparovsky, Head Agronomist at SMART! Fertilizer Management software, and an international expert in farm fertilizer management.
The origin of Citrus is believed to be South-East Asia. It is widely grown in sub-tropical regions, for example in the Mediterranean basin.
Among the citrus genus there are some well-known hybrids, such as orange, lemon, grapefruit, mandarin, clementine and pomelo.
Most of the commercial growth is in North America (Florida and California), South America (Brazil), Japan, Spain and Italy.
The root system of citrus is very shallow. Citrus can grow well on a variety of soil types, as long as the soil is well-drained. It grows well in clay soil or in containers, but will not tolerate saline conditions.
The ideal soil pH for citrus trees ranges from slightly acidic 6.0 to alkaline 8.0.
Lemon, Lime (Citrus aurantifolia) and other small-fruit citrus grow well in protected areas in cooler climate regions.
Grapefruits and other large-fruit citrus, however, may not sweeten in a cooler environment.
Optimum mean daily temperature: 23°C to 30°C.
Growth is markedly reduced above 38°C and below 13°C.
When temperatures drop below 0°C, even for a short time, flowers and young fruits tend to drop.
Citrus trees normally start bearing fruit from the third year after planting, but economic yields are generally obtained from the fifth year onward.
A grower should take notice of other fertilizing complexities. For example, soil temperature. Once the soil temperature is higher than 180C, it is recommended to add urea to the regular ammonium nitrate fertilizing.
For flowering in spring, a rest period or reduced growth is needed. In the subtropics, the low winter temperature induces this rest period, but in the absence of sufficient chilling, the rest period can be encouraged by water shortage.
Not all flowers end up producing mature fruits. During the flowering period, weaker, younger fruit tend to fall naturally. This is called 'June drop' in the northern hemisphere or the 'December drop' in the southern hemisphere.
Fruits take 7 to 14 months from flowering to maturity, corresponding to a harvest season from October /November to May/June in the northern hemisphere and from April/May to November/December in the southern hemisphere. All cultivars require proper fertilization for fruit development.
Citrus trees are sensitive to a high salt concentration in the soil.
Yield decrease due to soil salinity:0% at EC 1.7ds/m, 10% at 2.3ds/m, 25% at 3.3ds/m, 50% at 4.8ds/m, and 100% at EC 8 ds/m.
Grafting is commonly used for propagation of citrus trees. The method includes insertion of sprouts of a desired variety on to a stock grown from seed of another variety.
Normally citrus trees are transplanted. Planting distances differ according to a number of parameters, such as soil conditions, general topography, variety and the type of tree to be planted.
Planting spacing: generally, from 4 x 4m to 8 x 8m.
Tree density: varies from 200 to 800 trees/ha.
GET YOUR FREE TRIAL
Application of fertilizers has a great impact on almost all of the citrus growth stages. From the germination and roots development, through vegetative stage and ripening to maturing and fruits color break.
When providing nutrition to citrus trees, it is important to consider both the specific nutrients requirements of the plant and the soil conditions which it grows in.
Also, since different stages of the citrus trees require different quantities of nutrients, timing is crucial.
Giving the right nutrients at the right time will ensure high and quality yields, with no fertilizer waste and minimum environmental damage.
Citrus trees will grow poorly and produce sub-optimal yield and fruit quality due to excess or deficiency of nutrients. Analysis of potential nutritional problems should be part of a routine citrus-growing practice.
Testing nutrients in soils and leaves eliminates guesswork when creating a fertilizer program that is specific to your field conditions.
Leaf tissue analysis is the quantitative determination of the total mineral nutrient concentrations in the leaf. Tissue testing includes analysis of the following nutrients: nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), sulfur (S), manganese (Mn), zinc (Zn), copper (Cu), iron (Fe), and boron (B).
Chlorine (Cl) concentration is usually sufficient in most field conditions, but Cl may become excessive if soil or irrigation water is saline. Molybdenum (Mo) deficiency or toxicity is rare.
The goal of doing tissue analysis is to adjust fertilization program so that nutritional problems and their costly consequences are prevented.
Every citrus genus has its own nutrient expected content in the leaves in a specific time of growth. Every plant sample has to be taken from a certain tissue. Example nutrient leaf analysis standards:
The graph below presents the interpretation of tissue samples of orange genus variety Valencia. the tissues sampled are the mature leaves from the vegetative shoots.
Sampling time was before bearing first fruit.