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Blog at Jains - HOW MUCH WATER DOES MY CROP NEED? Part 6. Potato

India is the 2nd largest Potato producer in the world with a production of about 48.6 million ton from about 2.1 million hectares with 22.3 t/ha productivity. The major potato producing states are UP , West Bengal , Bihar, Punjab, Gujarat and Madhya Pradesh and they jointly contribute about 90% of the total potato production of the country. West Bengal tops in potato productivity with 24.7 t/ha followed by Haryana with 24.6 t/ha, Gujarat with 23.9 t/ha and Uttar Pradesh with 20.9 t/ha.

In a relatively short period of time Potato consumption has grown several fold in Asia, mainly India and China. Potato, historically is a staple diet in cold and the Americas, which now has changed as a major vegetable or snack food in Asia. This is not only the result of population growth, but the change of life style and consumer preference in Asia. The urban population of Asia , especially India see potato as valuable food and its demand increases parallel to the economic growth. Globally, the annual turn over of industrially prepared French fries is in the order of 11 million ton. Potato is also used as a source of starch in industry.

Potato is botanically known as Solanum tuberosum L., is one of the largest genera in the vegetable kingdom, with about 900 species. It is only six of these that grow filler potatoes.

Potato is a perennial but as a crop it is treated as an annual. It is vegetatively propagated by means of tubers. Now it is also propagated by true potato seed (TPS).The tuber is an enlarged underground stem produced on the end of a stolon.

Drip irrigation for Potato crop.

Inline drip system is suitable for Potato. The drip laterals are spaced on a skip row basis i.e. at 180 cm spacing where Potato is planted on ridges at 90 cm spacing. When the ridges are spaced at 1.2 m, an inline tube is placed at every row. Potato is also planted on raised broad beds 1.2 m wide. Two rows are planted on the bed at 90 cm space between the two rows. The drip line is placed in the centre of the bed serving the rows on either side. In case of inline the entire strip is wetted by placing drippers at 60 cm or 75 cm (based on soil texture) along the drip line.

Sprinkler irrigation for Potato crop

Controlled sprinkler irrigation is also suitable for Potato crop. In fact in certain parts of the country (Gujarat) farmers prefer sprinkler systems for potato.

Nevertheless, drip method is most efficient in terms water and fertilizer use efficiencies. From an application point of view fertigation thru drip is more precise and effective.

Different models of sprinklers of Jain are found suitable for Potato. One may select from Sprinkler models 5022 U, 501U, Super 10. The placement and discharges are given below.

Using sprinkler, water is applied every 3 or 5 days depending upon the soil texture and water holding duration of the soil. But irrigation with this system will create cyclic water excesses and shortages; both of which affect the growth and production of the crop. Irrigation efficiency is also lower (60%) than that of drip.

Sprinkler system is less expensive and farmers may find this more affordable than drip system.

Critical stages of water requirement for Potato

 In Potato, following stages are considered critical from point of view of maintenance of adequate moisture in the root profile; as even small shortages at any of these stages could result in proportionally very high loss in yield.

1. Germination (Immediately after sowing)
2. Stolonization (30-35 days after sowing)
3. Tuberization (45- 65 days after sowing)

Any let up in irrigation during this phase may give rise to variable size of tubers, with large proportion of chats & fewer ware grade tubers; which results both from uneven growth and uneven (non-synchronous) maturity of tubers at harvest.

Besides being wasteful, excessive use of water in furrow or flood irrigation results in lower yields and adverse environmental effects such as soil salinity and waterlogging. The main reasons for the poor yields in potato are improper irrigation management and long duration waterlogging. Therefore a precision technology like drip method is very essential for potato.

A large amount of water is lost in seepage and deep percolation in conventional method. Loss from deep percolation is estimated at 50 per cent in heavy textured clay soils and about 85 per cent in light textured loamy sands and laterite soils. The water consumption in these cases are more than the water requirement of the crop.

Where does all the water go after one irrigates a crop field? Water moves out of the field in 7 different ways after an irrigation that floods the field: 1.Direct evaporation from the water surface, 2. Drift of water away from the field due to wind, 3. Transpiration through the body of the crop plant (Mainly thru leaves), 4. Evaporation from the wet ground exposed to the atmosphere, 5. Run off of water from the field, 6. Infiltration to lower soil strata and 7. Deep percolation to far deep soil profile.

Among these, the essential components of crop water use are only two: transpiration and soil surface evaporation. Hence water use by crop is referred to as ETP, Evapotranspiration. As the crop grows the surface evaporation gets reduced and when the soil surface is fully covered by the canopy (leaf and tillers of the crop) there is only one dominant component of crop water use: Transpiration.

In precision Irrigation the water given should only be equivalent to ETP. The goal of perfect irrigation for is to reduce the components of wasteful water losses, like surface flow and general soil evaporation and percolation. In conventional irrigation major part of water loss are in fact the rest of the 7 listed above.

When a farmer asks the question, HOW MUCH WATER DOES MY CROP NEED? The answer is the ETP (evaporation plus transpiration). Accordingly, I have estimated the water required for a good high productive rice crop. The difference among the regions is due to difference in evaporation rate during the growing season of the crop.

How Much water I need for Potato crop?

Table Water requirement for Potato and Irrigation Volumes required to satisfy the WR in drip and sprinkler methods

Table Water Requirement of Wheat crop WR
Temperate Himalayan base region (Jammu) 116.1 1161  
Temperate Punjab Plains (Ludhiana) 593.0 5930  
Dry Central Plain region ( Indore) 338.5 3385  
Dry North-Western Plain (Banaskantha) 349.0 3490 5236 **
Northern Gangetic Plain (Agra) 640.8 6408  
Southern Peninsular Plain (Chitoor) 574.6 5746  
**In Banaskantha, Farmers prefer sprinkler systems
which has only 60% irrigation efficiency.
Potato under ridge and furrow flood irrigation m3/ha for 4 month crop

Precision wetting of the soil is maintained in irrigation for Potato through drip method. In conventional method water is applied till the field is flooded full or all furrows are filled up. Therefore a major portion of the applied water moves away from the field and the crop does not use it. This fraction of water is actually wasted and not used by the crop resulting in very low water use efficiency and water productivity.

For a 120 to 150 day growing period, Potato requires 1161- 6408 m3 water per hectare based on the evaporation rate of different locations. Yield under drip - fertigation assisted precision farming vary from 28-30t/ha. Applying water as per the estimates above is possible only through drip method of irrigation. For Banaskantha, Gujarat where sprinkler method is more popular among the farmers, the water use would be higher, 5236 m3/ha (and thru drip it would be only 3490 m3/ha). The difference is not related to the crop but only to the application method. Sprinkler is less efficient (60%) while drip method is 90%.

In conventional irrigation with flow in furrows, the whole season consumes an average of 7000 m3 in all the above regions and the average productivity recorded ranged from 16-18 t/ha only in farmers field.