Principles: Irrigation is an important factor and perhaps the costliest input in viticulture. The total amount of irrigation required for grapes is not high but the time of application and the amount should be determined by several factors, such as varieties of the vine growing, the density of planting, soil texture and depth, climate, and rainfall. Prevailing high and hot wind, cultural practices, manures, and fertilizers applied, mulching practice and intercropping if any done, plant protection measures adopted, anti-transpirant chemical if applied, and availability of irrigation water.
For grapes grown in the north of India, both frequency and amount of irrigation are needed to be high in summer. During the dormant condition of the vines in winter, irrigation is not required but 1-2 rounds of irrigation could be necessary at this time if the soil is dried so that bud sprouting is not hampered in the spring. During pruning of the vines, high soil moisture is not desirable and irrigation should be started in February- March soon after pruning is done. The amount of irrigation can be low but the frequency should be more after pruning because moisture stress during the growth of shoots results in their stunted growth with short internodes, the incidence of powdery mildew disease, and even drying.
Irrigation is avoided in blooming conditions but it has a great necessity during the development of the berries to prevent shriveling or drop or shot formation of berries. With the onset of the formation of berry ripening, irrigation should be discontinued as it may be delays the ripening of berries and causes their splitting.
In the South Indian vineyards, not more than three heavy irrigations are usually necessary after pruning in April and till the southwest monsoon sets in by June. During the rainy season, irrigation is not usually necessary and it should be started after the second round of pruning is done in October. But if the soil remains reasonably moist due to the late rain of the southwest monsoon, irrigation can be dispensed with until the middle of November when the berries would become the size of peas.
high soil moisture at this time can produce high vegetative growth and for this, the production of flowering shoots will be lesser. Nevertheless, one or two light irrigations just after pruning should not be disregarded if the soil goes dry. At the subsequent period, irrigations should be given depending on the soil moisture status and in general, should be applied at 12-15 day intervals from November to January and thereafter at shorter intervals till February- March.
Methods of Irrigation:
Almost all the irrigation methods that are practiced in fruit crops are known to be used in vineyards across the world. In some parts of India, basin, ring, and furrow methods of irrigation are in practice but these are now being replaced by other methods.
in the conventional ‘basin’ method (Fig 1), circular enclosures termed basins are made around each vine with raised soil bund at the periphery and its diameter is continued to increase during the first few years with the growth of the vines. All the basins are interconnected by sub-channels and the water flowing from the main channel is at first let out to its nearest basin. In this way, after irrigating the last basin, the remaining water moves to the drainage channel.
The method is beneficial in loose textured soil as it makes deep percolation of water and prevents stagnation of water around the vines. However, much of the nutrients are washed away from the basins to the drainage channels.
In the ‘ring’ method (Fig.2), a basin is made around each vine and the irrigating channels connecting them are laid out between alternate rows of vines. The basins lying on both sides of an irrigation channel are connected at the other side of the channels, laid in alternative rows of irrigation channels. Though the method can be somewhat better than the basin method, there is a difficulty in that, water stagnation can result in a basin if the percolation rate is slow and the delivery of water is not regulated.
In the ‘furrow’ method of irrigation (Fig 3), ridges and furrows are opened all the vineyard and irrigation water is made to flow slowly through the furrows. Hence, furrows should be made wide and shallow and their length should be restricted. The water is distributed uniformly through the furrows and it moves to greater depth also. Hence, in many Indian vineyards, where the soil water evaporation rate is higher than the precipitation received, the method is much more useful but it is not so where the soil is porous.
Regular choking of furrows by soil deposits is a hazard in these methods that necessitates their regular cleaning. However, a combination of the basin or ring method with that of furrow laid out in the inter-row spaces offers a greater advantage where the vine is highly vigorous and the percolation rate of water in the soil is high.
There is a drawback in the above methods and also in flood irrigation. This is the contamination of healthy vines with a very serious fungal disease, known as anthracnose. This happens when the pruned parts infected with the fungus are drifted away by the irrigation water and which on coming with the healthy vines causes them to infect. As a protective measure, a sufficiently raised small ring should be made with a soil bund so that water does not enter the ring (Fig 4). Thus, in the case of basin and ring systems, as shown in Fig 1 & 2, two rings that are bunded are to be made around a vine. One bund should be on the outer side and the other on the inner side and the irrigation water should be let out only between two rings. In the furrow method, the making of the outer ring is not necessary. Besides making the double rings, it is also necessary that the pruned parts of the vines should be removed from the vineyards instead of leaving them in the vineyard.
These protective measures are particularly advisable for grape varieties that are more susceptible to anthracnose disease, viz, Pusa seedless, perlette, delight black muscat, fakir, Thompson seedless, etc.
An expedient irrigation system of the present age that holds great promise in viticulture is ‘drip’ irrigation. In this system (Fig 5), irrigation water is delivered very slowly in drops to make them reach close to the water-absorbing feeder roots of the vines and thus, upholds the fact that every drop of water that lets out goes directly to the close vicinity of those roots instead of being wasted.
For high efficiency, the method is extensively used in many grape-growing countries now. The system consists of a filter station, a control panel having a network of sub and lateral pipelines, and emission points which are spaced at required distances on the pipelines. Water is made to flow through the pipelines at very low pressure and is discharged drop by drop from the drippers that are emitters. Sometimes the pipelines and the drippers are even buried under the ground and in such cases, short tubes of small diameters are connected to the emitters which open above the ground to make the dripping system.
There are many advantages of using drip irrigation. More pertinent ones are cited as:
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The high economy of water
better growth of vines in receiving only the required amount of water
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Control of weeds by preventing large part of the land from getting moistened
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Proper aeration of the soil
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Conservation of soil warmth
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Fertigation to make the economy of fertilizer application possible and so on
Many growers in Maharashtra have adopted this system in their vineyards. Despite advantages, difficulties also stand in the way of the smooth functioning of drip irrigation. Clogging of the dripper orifice is by far, a great problem that occurs particularly when narrowing of the orifice is done to allow a very low rate of water flow. On making the dripper outlets very narrow, they are often clogged and this necessitates washing of the pores. Clearing of those with dilute mineral acids is necessary to get rid of clogging but it may cause serious harm to the roots. Clogging is intense when ordinary water is used which contains impurities. To avoid this, water needs to be filtered before it is conveyed through pipelines and all these involve extra expenditure in its running condition.
Of the high cost of installation and running of drip irrigation, it is difficult for many grape growers in India to afford that, particularly those whose vineyards are not large. For such growers, the author advises a crude type of dripping method as has been devised and modified by him and described in the following.
The method (Fig 6) which may also be termed ‘pitcher’ irrigation is installed 0only by the use of large-sized earthen or plastic pitchers. To work out the device, a fine hole should be made at the bottom of each pitcher (Fig 6) preferably with a drill, and then it should be brought near the trunk of each vine to be irrigated.
The pitcher should be suitably held o 3 or 4 bricks placed on the ground respectively in the form of a triangle or square, ensuring that the bottom hole of it is not obstructed. It should then be filled with irrigable water and the water will dribble out through the bottom hole to function in irrigating by dripping. The water level in the pitchers needs to be examined regularly and refilled up to the level desired.
Or better effect, at least two pitchers should be used for a vine, placed on either side of it (Fig 6b). If necessary, fertilizers can be dissolved in the pitcher water in the desired concentration. In fertigation, the open mouth of the pitcher should be covered with a weighty type of nettling lid to prevent drinking of its content by birds (Fig 6c).
The pitchers to be used should be strongly built. They should also be regularly checked and replaced if found broken. The method has the drawback in that, regulation of water flow is difficult to be done for which over-dripping may result. Regular filling of the pitchers also involves labor costs. The method is not equally efficient as with the mechanized form of the device but may have been used to reduce irrigation costs, water is available in plenty and the vineyard is small in size.
Dr. Bibhas Chandra Manumdar
M.SC Agri, PH.D
Prtofessor in Horticulture institute of Agriculture Sciences
Calcutta University
Kolkata, West Bengal – 700029
Mob- 09830272846
Email.- profbcmazumdar@yahoo.com