SOIL MOISTURE DISTRIBUTION UNDER MICRO IRRIGATION - Management, Performance, and Applications of Micro Irrigation Systems - page 134

10.1 INTRODUCTION
Water is an important or perhaps the most important natural resource for survival of
life on the earth. Geographical area of India is 3.29 million km 2 , which is only 2.4%
of total geographical area of the world and has only 4% share of the world fresh water
to support over 16% of the world population. India receives annual average rainfall
of about 119 cm, which is highly variable temporally and spatially. Maximum rainfall
received during three to four monsoon months is spatially highly variable. The areas
receiving heavy rainfall during monsoon months invariably face water scarcity during
the nonrainy season every year. Therefore, it is absolutely essential that every drop of
water is conserved and efficiently used for long-term sustainability of scarce water
resource for survival of mankind.
Agriculture sector is the major consumer of water but its share is declining due to
its increasing demand for industrial and urban sectors due to ever growing population.
Consequently the share of water for agriculture is expected to reduce from the present
85 to 69% by 2025 [8]. Irrigation, one of the most important agricultural operations
performed in crop production consumes around 70% of the total available and usable
water resources. There is a considerable scope to increase the water use effi ciency and
agricultural productivity. Therefore, it is of paramount importance to maximize irriga-
tion effi ciency in order to use the available water resource for long-term sustainability.
Micro-irrigation is an effi cient and advanced irrigation method to enhance wa-
ter use effi ciency (WUE). The highest water application effi ciency (WAE) of about
90% may be achieved in drip irrigation methods resulting in 50-100% water saving
as compared to surface irrigation. Drip irrigation, which allows frequent application
of shallow irrigation depths, helps reduce soil moisture stress and achieve optimum
moisture regime leading to higher water use effi ciencies and better quality of produce.
In depth understanding of water application rate and soil properties, that affect the soil
wetting zone developed around the crop root zone, is important for proper designing
and management of drip irrigation system [3]. Water application rate is an input factor
in determining the soil water content around the dripper and the water uptake pattern
by plant [5, 7].
Moisture distribution pattern under a drip source is one of the basic requirements
for effi cient design of drip irrigation. The extent of soil wetted volume in drip irriga-
tion system determines the optimal amount of water needed to wet the effective root
zone. The amount of soil water stored in the root zone can be estimated by the volume
of wetted soil. Design parameters, such as percent of root zone to be wetted, spacing
and location of drippers, application rates, frequency and amount of irrigation, etc.
are governed by the moisture distribution patterns in the soil profi le in drip irrigation
which need to be thoroughly investigated. The wetting of soil volume is mainly a
function of the soil texture, structure, water application rate as well as the quantity of
water applied. The depth of the wetted volume should coincide with the depth of the
root system while its width is related to the spacing between drippers and drip laterals
[10]. Water movement in soil under drip irrigation is infl uenced by the type of soil and
rate of water application [9]. The soil hydraulic properties, number of drippers, drip-
per discharge and irrigation frequency greatly affect the shape of the wetted volume