Agriculture Reference
In-Depth Information
Table 1. Soil properties
particle size in percentage
of mineral parts
CaCO
3
(%)
% water
(v/v)
bulk density
(kg/dm
3
)
soil
2-50µm
>50µm
pF2.0
pF4.2
<2 μm
loam
19
49
32
25
36.3
20.4
1.45
clay
47
37
16
5
42
24
1.45
Table 2. Chemical composition of irrigation water (meq/l), electrical conductivity
(dS/m), and Sodium Adsorption Ratio (SAR)
Ca
2+
Mg
2+
Na
+
K
+
Cl
-
HCO
3
-
SO
4
2-
Water quality
EC(dS/m)
SAR
C (fresh water)
6.2
3.1
2.3
0.4
3.7
7.3
0.6
0.9
1.1
15 (15 meq Cl/l)
10.8
3.1
8.7
0.4
15
0.8
0.8
2.3
3.3
30 (30 meq Cl/l)
16.7
3.4
16.2
0.4
30
0.7
0.7
3.6
5.1
Just before sowing, 10 litres of fresh water were applied to all treatments to obtain a
sufficient emergence. Once the different qualities of water were applied, at each irrigation
surplus of water was added to provide a leaching fraction of about 0.2.
The evapotranspiration between the irrigation interval was calculated as the difference
between the amounts of irrigation and drainage water. Soil moisture sampling in the past had
shown almost the same moisture content after each irrigation, corresponding to the field
capacity.
To determine the soil salinity, the average chloride concentration of the soil water was
calculated from the balance of irrigation and drainage water (Katerji et al., 1992) and
converted into EC of the soil water by the equation ln EC = 0.824 ln Cl - 1.42, established for
this type of irrigation water and soil (van Hoorn et al., 1993). This EC value of soil water was
divided by two for the conversion into ECe. Owing to leaching at each water application, the
soil salinity remained almost constant or increased slightly from the start to the end of the
plant life cycle. The salt balance has the advantage of covering the whole soil volume of the
lysimeter, as compared to the point measurements of soil or soil water sampling.
3- Water Stress of the Plant
The parameters used to characterise the water stress of the plant were the leaf-water
potential and stomatal conductance. The leaf-water potential was determined with a pressure
chamber (Scholander et al., 1965) on one leaf per lysimeter (five leaves per treatment), taken
from the upper part of the canopy to avoid senescent leaves. The stomatal conductance was
measured with a diffusion porometer on the upper leaf surface of two leaves per lysimeter
(ten leaves per treatment).
These measurements were carried out at two time periods. During the entire vegetative
cycle, the predawn leaf-water potential was regularly determined at sunrise. Throughout the
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