Agriculture Reference
In-Depth Information
6
Fig. 10.4
Wheat yield versus
applied water
4
y = 1.7506 + 0.1317x - 0.0014x
2
a
2
0
0
10
20
30
40
50
60
Water applied, cm
irrigation) to satisfy individual versus community demand for more production.
Production functions are used to optimize on-farm irrigation and economic evalua-
tion of irrigation water application. The crop production functions are also essential
for improving water productivity (also termed as “water use efficiency,” WUE) and
effective allocation of water resources among crops/cropping patterns and soil types
in a region under conditions of water shortage.
10.4.3 Basic Considerations in Crop Production Function
The yield of dry-land crops can be considered in terms of water use, dry matter
production per unit of water use, and dry matter distribution to the grain or har-
vest index (or harvest ratio). In case of crop production, photosynthetically active
radiation (PAR) is used by the plant as the energy in the photosynthesis process
to convert CO
2
into biomass using the water, transpired by plant. Obviously, soil
evaporation is not a function of crop production. Thus, actually yield is a function
of transpiration. Since independent measurement of evaporation and transpiration
is hard and requires specific equipment and expertise, evapotranspiration (ET) is
normally used instead of transpiration.
10.4.4 Pattern of Crop Production Function
Crop yield relationship with seasonal evapotranspiration (ET) has been reported as
linear by many investigators (Singh et al., 1979; Mogensen et al., 1985; Musick
et al., 1994). The functional relationship between water applied and yield can
be quadratic, polynomial, or exponential (Hexem and Heady, 1978; Martin et al.,
1984). Zhang and Oweis (1999) developed quadratic crop production function with
the total applied water for wheat in the Mediterranean region. For the same amount
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