Introduction Success of mango orchards depends upon availability of rain or artificial irrigation during critical periods of tree growth and fruit development. Irrigation requirements are governed by various factors such as soil type, climate, root distribution etc. There are some other specific characteristics of mango and these characteristics should be taken into consideration to judge the irrigation requirements of mango. The deep and well spread root system of mango plant. Fruit-bud differentiation takes place in terminal shoots of eight to ten months. During fruit-bud differentiation and vegetative phase requirements are antagonistic. The fruit quality depends upon moisture content in soil during fruit development and maturity. The irrigation requirements of young and non-bearing orchards differ from the bearing orchards.

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Irrigation in Young and Non-Bearing Orchards The principal object of irrigation of young and non-bearing orchards is to boost fast and vigorous growth of the plants. In initial stage the root spread of the plants is limited. Light irrigation at frequent intervals is required to wet the soil. The non-bearing trees 4-5 years of age are irrigated at weekly interval. The interval of irrigation depends upon tree age, soil and climate. For the first six months after planting, interval should be 2 to 6 days, for 6 to 12 months old plant at weekly interval and 7 to 20 days till the plants attain bearing age. In light soil irrigation frequency is more than in heavy soils. During winter, the irrigation is specially required for protection against frost. In heavy soils, frequent irrigation causes damage to root system and stem so it should be avoided. But the interval should not be too long so that plant faces moisture stress and the growth and spread is checked.

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Irrigation in Bearing Orchards The irrigation of bearing orchards at regular intervals (10 to 15 days) is prime necessity during fruit set and for full fruit development. It is helpful in attaining full fruit size and reducing fruit drop. But to obtain good flowering, the irrigation during winter months (2-3 months) flower bud differentiation should be stopped. Irrigation during this period promotes vegetative growth, which will be detrimental to flowering. In North India 3-5 irrigations are required starting from February (at panicle emergence stage) to May (at full fruit size) at 15 days interval. In light soils, the interval of irrigation would be high during hot, dry and windy weather than in cold and calm atmosphere. The annual precipitation in most of mango growing regions varies from 100 to 250 cm. The most of these regions require little irrigation. Irrigation in mango orchards, whether it is young, non-bearing or in bearing stage, generally depends upon soil, climate, root system etc.

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Principles of Irrigation Irrigation in Relation to Soil and Climate The irrigation requirements of mango are closely related to soil and climate of the orchard. The fine textured deep and well drained soil generally found in Indo-gangetic plains, red soils of Dharwar and the laterite soils which have the property of retention of water, require less irrigation. Very fine textured and sticky soil, like black cotton requires no irrigation. Other groups of soils like light and medium textured require adequate surface irrigation, provided they are well drained. Any type of soil having water table upto 3 metre from surface requires no water as the roots of mango tree travel to this depth in search of water. Irrigation in mango is also associated with climate including humidity, rainfall and temperature. Mango orchards situated in humid tropics do not require irrigation irrespective of soil type while under dry climate having low humidity and high temperature, irrigation is needed at 15 days interval. Irrigation in Relation to Root System Mango tree has deep, well spread and extensive root system in most of the soils. The main root develops secondary roots that go to sub-soil layer. The one set of root system is found in the first 60 to 90 cm of the soil. This extensive type of root system helps the mango tree for its success and in most of the situations only light surface irrigation is sufficient. This extensive root system of mango draws and gets the moisture from far and wide. In some odd conditions, the extensive root system development is checked by hard pan rock, stony layer or the dwarfing rootstock used in grafting. In this situation root zone is kept restricted and ultimately it restricts the vegetative growth of plant. Trees under such situations require more frequent irrigation to get good yield and quality fruits. Irrigation in Relation to Fruit Bud Differentiation The carbohydrate accumulation in mango is accompanied by fruit bud differentiation and at this time there is no active growth, so little or no carbohydrate is utilized by plant. Irrigation promotes vegetative growth under favourable climatic conditions. Therefore, it is suggested that during fruit bud differentiation period irrigation of mango bearing plants should be stopped, otherwise irrigation during this period converts fruit/flower bud into vegetative bud which ultimately adversely affects the fruit yield. Irrigation in Relation to Fruit Set, Size and Quality Fruit set in mango does not have any relation to soil moisture unless the soil moisture is deficit for longer period. However, soil moisture influences the fruit size, quality as well as the drop of immature fruits. During fruit development period, under hot and dry climate, the irrigation prevents the drop of immature fruits. The moisture deficit in soil brings early maturity to fruits. So regular and normal irrigation to plants during fruit development and maturity period improves the quality of fruits. The fruits are of better size and more juicy from irrigated plants than those from tree under deficit soil moisture. Therefore, regular and timely irrigation of bearing plants becomes necessary.

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Methods of Irrigation A number of irrigation systems like basin, ring, furrow, flood, sprinkler and drip are employed. Each system has advantages and disadvantages as one system may be suitable for one set of conditions but unsuitable for another. Therefore, proper selection of the irrigation method is important for better orchard management practices. Basin Method In this system of irrigation, small circular basins are made around the tree trunks. These basins are connected with each other through a straight channel. The water passing through these channels touch the tree trunk directly. Such type of flow from plant to plant may cause damage and manures and fertilizers may be washed away with water and deposited at the end of the channel. The disease present in one plant may spread to other plants. In this way it increases the infection. The effective root zone is not properly irrigated. Therefore, this system is considered as defective one. Modified Basin System This system is similar to that of basin system except that instead of circular ring, the rectangular shape basin having bigger size is made. This system is also not adopted on large scale. Ring System This system is an improvement over previous systems. The irrigation channel is made between two rows of mango trees. Here the basins are kept small having circular shape. The individual basin is connected by sub-channel to the channel formed between two rows. Due to small size of basin, adequate amount of water is not accommodated which is sufficient for plant requirement. It is the disadvantage of the system. Modified Ring System This system is exactly similar to that of ring method. The only difference is the size of the ring. Here the ring is made upto the spread of plant canopy, which accommodates sufficient water, required by tree. Furrow Method of Irrigation Here the 2-3 furrows are made along the row on both sides. This system is suitable for the places where the flow of water is so regulated that it moves with slow speed. Here the plants are irrigated through lateral movement of water. Although this system is good but not adopted at large scale. Flood Irrigation This system is adopted in such orchards where sufficient water is available. Here entire area of orchard is wetted and meets the water requirement of tree and suited best to the extensive root system of mango. Trickle or Drip System of Irrigation This system is applied in those orchards where the water is in limited quantity and available water is used more judiciously. Here the irrigation to the mango plants is applied through drippers/emitters connected through microtube to the lateral. The laterals are connected to sub-main or main line in which water is supplied through a pumping unit from the source. Generally, for young mango orchards two drippers of 81/ha are placed at a distance of 1.0 m on lateral line. The full grown trees are supplied water with double lateral lines and two drippers on each lateral line are placed at 1 to 1.50 m distance. The young mango plants require 9-12 litre/day/plant water for better growth. The plants of 3-6 years, 6-10 years, 9-12 years and full grown trees require approximately 30-35 litre, 50-60 litre, 80-90 litre and 120 litre/day/plant. This system has several advantages such as plant attains quick growth, water saving, weed control, labour saving, easy nutrient application and increase in yield of good quality fruits. The only disadvantage is the high initial cost of installation.

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