Classification crop: Fruit crops trees > Citrus fruits
The orange (Citrus sinensis L.) belongs to the Citrus genus, of the Rutaceae family. It is an ancient hybrid, probably between pomelo (Citrus maxima) and mandarin (Citrus reticulata), but for centuries it has grown as an autonomous species. it is propagated by grafting and cutting.
It is mainly cultivated for the production of fruits to be destined for fresh consumption or for industrial transformation, but also for ornamental purposes.
It has different origins and almost always fall in a large area of ??Southeast Asia.
It has spread to many other parts of the world, from the Mediterranean basin to America and South Africa. In Italy it has found an area of ??choice in the southern regions, due to the mild climate and the type of soil.
The main producing region is Sicily which alone produces 62% of the oranges. Calabria (20%), Puglia (6%), Basilicata (4%), Sardinia (3%), Campania (2%), Lazio (1%) and other regions (2%) follow in order. ).
It has a low resistance to low temperatures and prefers temperatures between 13 and 30 ° C. It suffers frost damage with temperatures just below 0 ° C. Temperatures above 35-37 ° C are harmful, especially if they occur in coincidence with conditions of low relative humidity and during the fruit setting phase.
The presence of strong and persistent winds can cause serious damage (drying of the leaves and young shoots, mechanical breakage of branches, wounds from rubbing on the same fruits). To overcome these problems, we often resort to windbreaks (live or dead).
In our climates, to obtain a valid production, irrigation is almost always necessary.
Orange prefers loose or medium-textured soils, deep, fertile, well-drained (it cannot stand water stagnation), with a pH between 6.5 and 7.5 and well endowed with organic substance. It avoids too clayey, calcareous and salty soils.
In general, the removal of nutrients also depends on the age of the plant.
In order to calculate the dose of fertilizers, in adult plants in production, can be considered only net removals, while in young plants, in whose soil an adequate cycle of mineralization of fallen leaves and pruning wood has probably not yet been established, it is better to use total removals. Nitrogen represents the most important element. A substantial part of the absorbed nitrogen returns to the soil - with leaves and pruning - while the quantities removed from the fruit depend very much on the quantity of the production itself. Unlike other arboreal fruit crops, the removal of potassium is significantly lower than that of nitrogen and calcium, also in relation to its lower concentration in the fruit.
The production of orange crops is very variable: they can reach and exceed 40 tons / ha, especially with late varieties such as Valencia. The average yield varies between 20-30 tons / ha.
For production of about 20-22 tons/ha, the annual net removals can be approximated by multiplying the expected fruit production (in tons of fresh weight / ha) by a coefficient of 1.5 for nitrogen, 0.2 for phosphorus, 1.0 for potassium, 0.7 for calcium and 0.1 for magnesium.
Nitrogen is a fundamental component of enzymes, vitamins, chlorophyll and other cellular constituents that are essential for the growth and development of crops. Therefore, nitrogen is one of the most important nutrients for obtaining high yields in citrus production.
In the soil, the analytical value of total nitrogen is found for the most part (97-98%) as an organic substance and is not available to plants until after the mineralization process. The remaining 2-3% is found in mineral form (majority in form of ammonia retained by the Cation-Excange Capacity of the soil) and available for cultivation.
Crops with adequate nitrogen levels have a fruit with a thicker skin and therefore with a reduced risk of mechanical damage and the incidence of diseases. Too much nitrogen can lead to too thick a peel, reducing the juice content and fruit size.
Much of the increase in yield is due to the increase in the number of fruits. Nitrogen is usually administered in 3-5 applications during the growing season of the plant.
Phosphorus is a component of nucleic acids and lipids and plays an important role in the metabolism, energy transfer and transport of photosynthesis products.
The absorption of Phosphorus occurs throughout the growth period, after flowering and until the fruit matures. Good availability is important during periods of active root growth, for example in the spring.
The limited availability for crops is due to the fact that phosphorus tends to immobilize in the soil mainly due to its reaction as phosphate with calcium.
The lack of phosphorus occurs rarely, but when this occurs it can cause a reduction in flowering, and a consequent drop in production and reduced fruit size, with a lower juice content. Poor phosphorus leaves turn bronze in color and are smaller than normal. The older leaves necrotize at the edges and at the tip.
Potassium is characterized by high mobility in plants at all levels: cellular, histological and in long-distance transport via xylem and phloem. It is also extremely important in the translocation of photosynthesates.
Together with nitrogen, potassium is one of the most important nutrients for citrus production.
Potassium is responsible for various internal and external qualitative characteristics of the fruit, such as size, skin thickness or color.
One of the first symptoms of potassium deficiency may be the appearance of yellow / bronze colored spots along the edge of the leaves. These spots grow and come together until they completely cover the leaf, which thus assumes the same yellowish color. Fruit rupture is another symptom of low potassium levels. To avoid the occurrence of such problems, it is necessary to periodically analyze the tissues of the leaves. The administration of potassium contributes to the development of vigorous dark green leaves.
In some cases it may be that the application of K to the soil may be ineffective, for example on clay soils with a high ability to fix the K and where there are high levels in the soil of Calcium and Magnesium. In this case, foliar application of potassium is necessary.
Calcium is a fundamental component of cell walls and also has a direct influence on the regulation of enzyme systems and on the activity of phytohormones. Calcium also influences the elongation of the pollen tubes and the formation of seeds.
Calcium intake is important, especially during the early stages of growth and throughout the period of increase in fruit size. Calcium is the element present in greater quantities in citrus leaves and its repeated administration during the season produces high yield with optimal fruit quality. Calcium is the third most used nutrient. It is important to take note of the level of nutrients consumed in the fruit. The amounts vary significantly between the various types of citrus fruit.
In the event of a calcium deficiency, the leaves may exhibit symptoms in the internerval areas similar to those caused by the iron or manganese deficiency, but they are quite rare. Deficiency is defined when the calcium level in the leaves is less than 1.6%. However, trees lose vigor and begin to lose leaves when the calcium level in the leaves drops below 3%.
Magnesium is necessary for many processes in citrus trees, in particular for the production of chlorophyll. The yield increases are mainly due to the increase in the weight of the fruit. However, an optimal use of magnesium also increases the juice content in the fruit.
In the event of magnesium deficiencies, the leaves present internerval chlorosis at the tip and margins, while the base of the leaf remains green. Such symptoms occur most often in cultivars that produce higher levels of seeds in fruits, which require more magnesium for nutrition. Magnesium deficiencies are most likely to occur in degraded and acids soils that naturally contain low levels of magnesium. Absorption can also be reduced in calcareous soils with high levels of free calcium.
For a correct fertilization, soil analysis is always necessary, to be integrated with the foliar analysis that allows to know what the nutritional levels are reached by the plant and thus diagnose any situations of deficiency or excess of the different nutrients. For foliar analysis, the sampling must be done at the end of summer-early autumn, taking leaves issued five-seven months before from non-fruiting branches.
Irrigation
The Mediterranean environment is characterized by low rainfall, moreover concentrated in the autumn-winter period. The use of irrigation is therefore absolutely necessary to meet irrigation needs in the summer.
Furthermore, citrus fruits are particularly demanding towards the quality of irrigated water; in fact a high content of chlorine, boron and sodium and other elements cause a characteristic symptomatology due to their accumulation in the soil and in the leaves and in severe cases a reduction in the quality and quantity of production. The tolerance towards the various salts is highly variable in relation to the rootstock and the species.
Regarding irrigation systems, in addition to the traditional methods of basin and furrow irrigation, under canopy sprinkler and drip or micro-irrigation is currently preferred.
Weed management
For the control of weeds, responsible for exercising a strong watercompetition in the spring-summer period, weeding is generally practiced (rarely mulching), generally seasonal, i.e. it is implemented only in the spring-summer period after having been processed. superficially, the herbs grown during the previous two seasons were shredded. In this way, during the year there is the coexistence of grassing and weeding, which allows you to not give up the benefits of the first (e.g. accumulation of organic matter).
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