Water Resources Management - Practices of Irrigation and On-farm Water Management - page 166

C X = ( C i × r i ) + ( C j × r j ) (5.4)

where

C X = salt concentration of mixed water, mg/l

C i = salt concentration of first category of water, mg/l

r i = proportion of first category of water

C j = salt concentration of second category of water

r j = proportion of second category of water

and r i + r j =

1

Alternate Irrigation of Saline and Fresh Water

Fresh and saline water can be applied in alternate sequence (fresh-saline-fresh-
saline) to increase irrigable water and minimize salinity hazard. In such a practice,
some sort of stress hardening is developed in plants for salinity stress.

Irrigation with Saline Water at Less Sensitive Growth Stages

Where fresh water is unavailable or very costly, fresh water should be applied when
it is essential. All growth stages of crops are not equally responsive to salinity stress.
Hence, irrigation with fresh water at most sensitive growth stage(s), and irrigation
with saline water (or a mix) at relatively insensitive stage(s) can facilitate reasonable
plant growth and yield.

Rainwater Harvesting at Farm Ponds, Lakes

The source of all water is rain. The harvesting of rainwater simply involves the col-
lection of water from surface on which rain falls and subsequently storing this water
for later use. As a definition, it can be defined as the collection of rainfall or rainfall
runoff for agricultural production, or domestic purposes, or livestock watering. In
areas where there is inadequate groundwater supply, or surface resources are either
lacking or insufficient, rainwater harvesting offers an ideal solution. Countries like
Germany, Japan, United States, and Singapore are adopting rainwater harvesting. In
urban areas, rainwater harvesting from the building roof and storing it underground
can serve the need of about 40% of the demand of the urban people during rainy
season. Productivity of rainfed agriculture can be improved through supplemental
irrigation via water harvesting. Rainwater harvesting in existing local ponds, and
using them for dry season cropping (particularly low water demanding crops, such
as pulses, oilseed, wheat), seems a prospect in dry areas. Ali and Rahman ( 2009 )
found that 20:1 ratio of land area to pond area is sufficient to cultivate low-water
demanding dryland crops (other than rice) in saline area. The details of water har-
vesting procedures have been discussed in Chapter 11 ( Water Conservation and
Harvesting ), Volume 1.