Introduction

Citrus is native to a large area, which extends from Himalayan foot hills of northeast India to northcentral China, the Philippines in east and Burma, Thailand, Indonesia and New Caledonia in Southeast. In India, in terms of area under cultivation, citrus is the third largest fruit crop after Banana and Mango. The average yield of citrus fruits in India is alarmingly low (8.8 t/ha) compared to other developed countries like Indonesia, Turkey, Brazil and USA (22-35 t/ha). Among mandarins, Nagpur mandarin (Central India), Kinnow mandarin (North–West India), Coorg mandarin (South India) and Khasi mandarin (North-East India) are the commercial cultivars of India. Whereas, Mosambi (Maharashtra), Sathgudi (Andhra Pradesh) and Malta and Jaffa (Punjab) are the sweet orange cultivars traditionally grown.

Scope for Citrus Cultivation and its National Importance

Citrus cultivation in India is plagued with various problems due to limiting growing conditions, limiting water resources and high incidence of pests and diseases warranting great care from planting till the plants come to bearing in order to sustain a productive life of a minimum of 15-20 years. There is growing interest/awareness among the citrus growers for adoption of latest technologies for commercial cultivation of citrus. The National Research Centre (NRC) for Citrus (ICAR), Nagpur has come out with the package of practices for citrus cultivation in different regions of the country. In the present bankable project on citrus, recommendations of the NRC for Citrus and the views of the citrus growers and their experience has been taken into consideration. The distribution of major citrus fruits is given in Table 1. Table 1 : Distribution of major citrus fruits Global Scenario National Scenario Mandarin 13% 44% Lime & lemon 10% 28% Sweet orange 71% 18% Others 6% 10%

Technical Requirements of Citrus Cultivation

1 Climate

Citrus fruits in India are cultivated under varied agro-ecological conditions right from arid and semiarid areas of southwest region to humid tropical climate of northeast India. Citrus trees are evergreen, grown in truly subtropical climates of the world although in tropical regions of the world they tend to produce cyclic growth flushes and hence regulating cropping in tropical areas for forcing them into concentrated bloom needs judicious management of water deficit stress according to soil type and growing season. Citrus fruits grow best between a temperature range of 130C to 370C. Temperatures below – 4 0C are harmful for the young plants. Soil temperature around 250C seems to be optimum for root growth. High humidity favours spread of many diseases. Frost is highly injurious. Hot wind during summer results in desiccation and drop of flowers and developing fruits. Barring these limitations citrus is grown in all subtropical and tropical areas of the world. The subtropical climate is best suited for citrus growth and development. Khasi and Darjeeling mandarins are grown in high altitudes upto 2000 m as it is adapted to a cooler climate.

2 Soil

Citrus plants are grown in a wide range of soils ranging from sandy loam or alluvial soils of north India to clay loam or deep clay loam or lateritic/acidic soils in the Deccan plateau and north-eastern hills. Citrus orchards flourish well in light soils with good drainage properties. Deep soils with pH range of 5.5 to 7.5 are considered ideal. However, they can also be grown in a pH range of 4.0 to 9.0. High calcium carbonate concentration in feeder root zone may adversely affect the growth.

3 Planting Material

Availability of quality planting material is of utmost importance in citrus cultivation. Citrus plants are very sensitive to various biotic and abiotic stresses. Therefore selection of an ideal rootstock is a continuing challenge for the citrus industry of India. Currently used rootstocks viz. rough lemon and Rangpur lime have gone through a lot of variation over the last five decades. Therefore ideal selections developed from the conventional rootstocks by National Research Centre for Citrus (NRCC), Nagpur and at other places under State Agriculture Universities may be obtained for propagating quality planting material. For budwood selection, disease free mother plants developed from the elite progeny of known pedigree through shoot tip grafting method available at NRCC, Nagpur may only be used. Primary nursery beds are prepared on light fertile soils or in the HDPE trays under shade net structures. Selection of nucellar seedlings is done by eliminating weak seedlings, off types and non uniform seedlings in 2-3 stages in the nursery beds. Secondary nursery seedlings may be raised in polythene bags also as they become ready for plantation in the main field after attaining the height of about 30-40 cm after one year.

4 Land preparation

Land needs to be thoroughly ploughed and levelled. In hilly areas, planting is done on terraces against the slopes and on such lands, high density planting is possible as more aerial space is available than in flat lands. Since citrus trees are highly sensitive to water logging and water stagnation during rainy season providing drainage channels of 3-4 feet depth along the slopes around the orchard is essential.

5 Plant density

a. Mandarin (Citrus reticulata Blanco) Normal spacing – 6 m x 6 m ; Plant population – 277 / ha b. Sweet orange (Citrus sinensis Osbeck) Normal spacing - 5 m x 5 m, 5.5 x 5.5 m; Plant population – 400/330 per ha c. Limes/lemons (Citrus aurantifolia Swingle & Citrus limon) Normal spacing – 6 x 6 m / 5 x 5 m, Plant population – 277/400 per ha In light soils, spacing will be 4.5 x 4.5 m or 5 x 5 m

6 Planting

The best season of planting is June to August. Pits of the size of 1m x 1m x 1m may be dug for planting seedlings. 15-20 kg of FYM and 500 g of super phosphate is applied per pit while planting. With good irrigation system, planting can be done in other months also.

7 Irrigation

Citrus requires critical stage watering in the initial year. It further reduces fruit drop and increases the fruit size. Diseases like root rot and collar rot occur in flooded conditions. Light irrigation with high frequency is beneficial. Irrigation water containing more than 1000 ppm salts is injurious. Quantity of water and frequency of irrigation depends on the soil texture and growth stage. Micro irrigation systems not only saves water and nutrients but also ensure good retention of fruits during crucial stages of crop growth in March – April even in situations where water is not a limitation.