Introduction Citrus (Citrus spp) is grown in almost all the states of India. Although the citrus industry in India has faced many challenges, there has been a consistent increase in area and production owing to the awareness for sustained production. Citrus fruits, consisting of mandarin orange (Citrus reticulata Blanco), sweet orange [C. sinensis (L.) Osbeck] and lime [C. aurantifolia Swing le] are grown commercially in tropical, subtropical, arid irrigated and mountainous regions in varying soil and weather conditions. Citrus is grown practically all over India. However the states of Andhra Pradesh, and Maharashtra have the largest share. Although citrus trees on the whole do well in dry climate, with a rainfall between 75 and 125 cm, certain species, such as pummel and certain mandarin oranges, thrive in heavy-rainfall areas of Konkan, Assam and Coorg.

Citrus trees the grown in almost all kinds of soil, varying from heavy black soils to shallow open soils. Some of the varieties of citrus seem to adapt them-selves to soil conditions better than others. They thrive in free-draining alluvial or medium black soils of loamy texture. A hard substratum or a sticky impervious layer is very injurious. Soils having a high water-table should be avoided. Click on individual citrus fruits to view their basics:

(Citrus limon (L.) Burm. f) is not cultivated to any great extent in India, as it requires a comparatively cool climate for regular bearing. Its fruit is not so highly flavoured as that of sour lime. The lime (Citrus aurantiifolia Swingle), both sour and sweet, known as kaghzi nimboo and mitha respectively, are more prized in India than lemon. Sour lime is propagated mainly from seed. Budding on rough lemon rootstock, layering and moreotting are also practiced to some extent. The tree is susceptible to frost. It flowers twice a year in February-March and again in August. The main crop is obtained in August from the first flowering. The second crop is ready in the following February. The propagation of sweet lime is done from mature wood cuttings, which root readily. It can also be propagated from seeds and the seedlings, usually come true to type. Planting of limes and their pruning, manuring, etc. are the same as for the sweet orange.

Mandarin is largely grown in Arunachal Pradesh, Karnataka, Maharashtra, Meghalaya, Nagaland, Punjab, Tamil Nadu, Tripura and West Bengal. In Punjab, Kinnow is a commercial cultivar, whereas ecotype of Nagpur mandarin is grown in different regions known by different names..

Climate and Soil

Santra or mandarin orange (Citrus reticulata Balanco) grows successfully in all tropical and subtropical parts of the country. It tolerates more humidity in summer and winter than the sweet orange. It is grown under rain-fed conditions in Coorg, Wynad tract, Palni Hills and the Nilgiris in the south between elevations of 600 and 1,500 metres. In Assam, the main centres of production are the Khasi, Jaintia and Lushai Hills. The region around Nagpur (elevation about 370 metres) produces a superior quality of mandarins. It is mainly grown under irrigation. In Punjab, its cultivation is confined mainly to the submontane districts up to about 600 metres. It can be grown successfully on a wide range of soils, but the ideal soil is medium or light loam with slightly heavier subsoil. Heavy black soil, underlain with murram and having good drainage, is also suitable. In the Khasi Hills of Assam, oranges are grown on sandy or gravelly soils.

Varieties

The important varieties cultivated on a commercial scale are the `Nagpur’ orange, the `Khasi’ orange, the `Coorg’ orange, `Desi Emperor’ and the `Sikkim orange.
Propagation

The propagation of mandarin orange is largely through seed, except the `Nagpur’ and `Emperor’ varieties, which are propagted by budding. Like other citrus species, the seed is polyembryonic. Therefore, while propagating by seed, the sexual seedlings, which are usually stunted, and poor are rogued out and the rest that are produced from the cells of the nucellus are allowed to grow. The seedlings, thus selected, are more or less uniform in growth and production. They are, however, late in bearing and remain tall and slender. Budded plants do not suffer from these defects. The santra orange is usually budded on rough lemon (jambhiri, Soh-myndong or jatli khatti) rootstock. The variety `Emperor’ is budded on the kharna khatta rootstock. Studies at the Citrus Experiment Station, Coorg, of the Indian Institute of Horticultural Research, has shown that Trifoliate, Rangpur lime, Kodakithuli and Troyer citrange are good rootstocks for mandarin.
Planting

In the hills and humid regions, where plantings are generally done on steep slopes, the land is properly terraced. In the plains, where the trees have to be irrigated, the land should be leveled. The trees are usually transplanted during the monsoon. In heavy-rainfall areas, the planting is generally done at the end of the heavy rains. They are planted 4.5 to 6 metres apart.

Pruning Prune young trees to build up a strong framework, as recommended for sweet orange. The bearing trees require little or no pruning. Undesirable growths, like water-shoots and crossing branches, should be removed once or twice a year. In Bombay-Deacon, root exposure or resting treatment is given to santra trees to make them flower to order. The treatment is the same as for the sweet orange.
Manuring

Farmyard manure, 20 to 25 kg per tree, is applied at planting, together with about half a kilo of each of N, P and K per tree may be applied in the first year after planting, and the dose is gradually increased to 0.45 kg of each of N and P and to 0.90 kg of K per tree in the seventh year and kept constant thereafter. The dose of farmyard manure is increased to 50 kg per tree. It may be replaced by green manuring. In northern India, manuring is generally done in winter, whereas in Bombay-Deccan it is done before the advent of the monsoon or at the time of root exposure.
Water Management

Citrus plants responds well to irrigation. Water management constitutes an important input in citrus orchard, which determines productivity and longevity. Normally no irrigation is practiced in heavy rainfall areas of North-Eastern states. Plants that receive 1 or 2 irrigation during dry period have healthy growth and produce heavier fruits in these areas. At the same time consecutive irrigation without definite period of soil-moisture stress is detrimental to crop yield, as such as situation leads to more vegetative growth. Monitoring of soil moisture is effective for regulating flowering and fruiting in acid lime under tropical situation. Of late drip irrigation is becoming very popular in water-scarce area of Maharashtra, parts of Tamil Nadu and Andhra Pradesh. Many young citrus orchards were planned and planted wit drip system of irrigation. The economic analysis of these 2 systems favoured for the use of drip irrigation, which is viable. The system improved the yield, uniformity in fruits and gave brilliant quality of fruits in respect of shape, colour and edible quality. The growers apply the nitrogenous fertilizer through the drip which further economize on the fertilizer use.
Harvesting

Seedling trees bear their, first crop in the eighth year and the full crop from the tenth year onwards. Budded trees start bearing from the fourth year and full crop is had from the seventh year onwards. The harvesting periods differ in different parts of the country. While picking the fruit, the stem-end should be cut close to the fruit without damaging rind. Packing is done by putting the fruits of different size grades in separate wooden crates.

(Citrus sinensis (L.) Osbeek) is grown under both subtropical and tropical conditions.
Area of Cultivation

In sweet oranges, Musambi is largely grown in Maharashtra, whereas Sathgudi or Chini is the basis of commercial cultivars in Andhra Pradesh. Blood Red Malta, Malta, Jaffa and Valencia are grown in Punjab.
Season

Dry and arid conditions, coupled with distinct summer and winter having low rainfall, are most favourable to the growth of the sweet orange. Rainfall seems to be unimportant if irrigation is provided, but atmospheric humidity exerts a great influence.
Soil

The sweet orange can be grown on a wide range of soils, from heavy clays to very light sands, with pH ranging, from 6.0 to 8.0. The tree is particularly sensitive to high concentrations of salts and cannot stand water-logging.
Varieties

The important varieties of sweet orange grown in each, region are `Blood Red’, `Pineapple’, `Hamlin’, `Jaffa’ and `Valeneia Late’ in northern India, mosambi in Western India and `Sathgudi’ and `Batavian’ orange in southern India.
Propagation and Planting

Usually, propagated by budding. The most suitable rootstock is Jamberi or jatti khatti. For `Pineapple’, `Hamlin’, `Jaffa’ and `Valencia Late’ varieties, kharna khatta also provide a suitable root-stock. The trees are planted 6 to 7.5 metres apart each way in January or August-September in the north and in July-August in the south. The bud-union should be kept at least 15 cm above the ground while planting.
Pruning

The pruning of citrus-trees begins in the nursery. All branches that start within a few centimetres of the union are removed, leaving about half a metre of clean straight stem with a few well-placed branches. All unwanted branches are removed once a month during the first year after planting, and once in two to three months in subsequent years. The bearing trees require little or no pruning. After the crop is picked, the branches touching the ground should be cut close to the laterals so that no stubs are formed. All diseased injured and crossing branches, water-sprouts and dead wood should be removed periodically.

Root Exposure

In the Bombay-Decean region root exposure is given to the year. Water is withheld for about two months in advance of the normal flowering season, and after about a month, the roots are exposed by removing about 10 cm of the soil in the case of light soils and about 20 cm in the case of heavy soils. After about 10 days, the soil is returned mixed with manure, and a light irrigation is given. After four or five days, a more copious watering is given, followed by 10 days later by the full dose of water. In the case of light soils, the withholding of water without root exposure is sufficient to check vegetative growth and force blossoming. In southern India, no root exposure is given nor is it feasible. In the north, the root-exposure treatment is not necessary as the trees normally rest in winter and flower once a year. It should be mentioned that in most situations, the root exposure of citrus trees is a devitalizing process and should be resorted to only under expert advice and direction.

Manuring

Manuring may be followed as in the case of the santra orange.

Water Management