The objective of irrigation is to apply the required quantity of water as per tree requirement at the right time. The frequency and amount of irrigation need depends on the type of soil, its properties, prevailing climatic conditions, rainfall and distribution, age and size of trees.

Mango tree is evergreen grown in tropical and subtropical regions of the world. Due to its superb juicy, tasty and colourful fruit, mango is known as the ‘king of fruits’.

In Pakistan, mango is grown over an area of about 10,000 hectares with an annual production of around one million tons. Pakistan ranks fifth with four per cent of world’s total mango production.

Mango tree is considered drought resistant to some extent; however soil moisture influences the fruit size, quality as well as the drop of immature fruits. Under hot and dry climate, irrigation prevents drop of immature fruits during fruit development period. It is also observed that moisture deficit in soil results in early maturity to fruits resulting in poor quality. Properly irrigated trees have fruits of better size and juicier than those trees with soil moisture deficit.

Mango orchards are usually irrigated by conventional methods such as flood, basin, ring and furrow. However, some of the progressive growers have changed irrigation strategies and now they are irrigating their orchards with modern micro-irrigation methods such as drip and under tree sprinkler system. 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 an irrigation method is imperative for better yield and quality of mango production.

The water requirement of a mango tree increases with the increase in the age of a tree and becomes constant when the full canopy has been developed at the age of about 20 years to 25 years. In light soil (sand to sandy loam) irrigation frequency should be more than in heavy (clay) soils. The more sandy and gravelly the soil, the more frequent irrigations it needs.

Depending on soil type, climatic conditions, plant density, variety, size and age of trees, the annual water requirements vary from 50 to 400 liters/day/plant. Plant water requirement increases dramatically during fruit development. The moisture can be extracted by plant within 2-7 days depending on soil type, age of tree and climatic conditions.

As per mango tree phenology, there are five stages of life cycle viz. flowering, fruit development, vegetative growth, root development, and dormancy. About 80 per cent water is required by tree during flowering and fruit development stages. It is advisable to stop irrigation at least 10 to 15 days before harvest. Irrigation during maturity will stimulate growth of new buds and leaves resulting in poor fruit quality.

During visits of various mango farms located in outskirts of Hyderabad city it was observed that mango trees were facing dry stress at some farms which were irrigated with under tree sprinkler irrigation system having 3-4 jet sprinklers per tree. Due to lack of proper design and management, the system did not deliver the required quantity of water to the entire diameter of the canopy. Only about half of the diameter of canopy cover received the required water (field capacity), while remaining area was under water deficit.

Application of water only on half of root’s lateral spread did not meet the requirements of the tree at maturity under the scorching heat of Sindh. Thus, plant leaves appeared unnourished with wilted tips. Lack of required moisture content in root zone caused higher fruit drop, poor fruit quality and lower yield.

While selecting an irrigation system, it is advisable to consider available water resource, soil type, age and canopy of tree and climatic conditions of the area. Basin system has given better results where sufficient water is available. It is advisable to irrigate the entire soil surface up to plant canopy. With limited water resources and climatic conditions where annual evaporation is higher than annual rainfall, drip (trickle) irrigation is more appropriate than that of under tree sprinkler system.

It is better to make sure that the irrigation system is designed to deliver the seasonal and peak water requirements throughout the life span of the irrigation system.

Technical staff to run the system should have quantitative knowledge of tree water requirements and relationships among soil, water, weather and plant characteristics for proper irrigation scheduling and management. It is also advised to flood irrigate once the entire land of orchard with so as to avoid any salinity development at the periphery of canopy due to drip irrigation.