HOW MUCH WATER DOES MY CROP NEED? Part-2

B y: Dr.P.Soman, Posted: April 2020

Water resources are drying up. Humans find it challenging to measure, and estimate water use by the crop. They are also looking for opportunities to improve water productivity, by conserving water or reducing its consumption. At this point one started asking ‘ How much water does my crop need ?’

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 leaf bearing branches 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 is to reduce the second component of water loss, surface evaporation. 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 DOES MY CROP NEED? The answer is the ETP (evaporation plus transpiration). Accordingly I have estimated the water required for a good high yielding Banana crop. The difference among the regions is due to difference in evaporation rate during the growing season of the crop; the 11 month irrigation period for Banana.

How Much water I need for Banana crop?

  WR mm WR m3/ha
Peninsular region (Theni, TN)
October planting
866 8663
Dry Peninsular region (Cudappah, AP) June Planting 1621 16210
Central dry Plain region (north Jalgaon) June planting 1094 10944
North temperate region (Punjab/UP) July Planting 745 7456

Precision is maintained in irrigation for Banana through drip method. In conventional method water is applied till the field/or field channels between rows of Banana are filled up with water and therefore a major portion of the applied water moves away from the field. 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 12 month period, Banana requires only 8663 m3 to 16210 m3 water per hectare to produce 85 - 105 t/ha yield under drip –fertigation assisted precision farming in the central and south peninsular India. Its requirement is 7456 m3 in north temperate region where low temperature restricts growth for 3–4 months. In this region the productivity is also comparatively low, 78–85 t/ha. Applying water as per the estimates above is possible only through drip method of irrigation. In conventional irrigation system the whole season consumes 19000– 22000 m3 in all these regions and the productivity of sugarcane ranged from 40–52 t/ha only.

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