Agriculture Reference
In-Depth Information
TABLE 7
Effects of irrigation systems on soil aggregation.
Irrigation
systems
MWD
(mm)
Aggregation
(%)
Season
Drip
Low-head bubbler
Modified gated pipes
16.23
17.09
13.86
36.15
38.76
27.79
2002/2003
LSD 0.05
0.01
0.001
Drip
Low-head bubbler
Modified gated pipes
17.6
13.34
15.21
32.93
32.05
31.91
2003/2004
LSD 0.05
0.02
0.002
Both MWD and aggregation percentage were affected each irrigation system. Ac-
cording to the value of the MWD and Agg.%, irrigation systems followed the ascend-
ing order of GPIS<DIS<LHBIS at the beginning of season 2002/2003. Differences in
both the MWD and Agg.% between any two irrigation systems were signifi cant at the
5% level. In other words, the changes in both MWD and Agg.% were (17.1; 30%) and
(23.3; 39.5%) when DIS and LHBIS were compared with GPIS, respectively, at the
beginning of season 2002/2003.
At the end of season 2003/2004, irrigation systems followed the order of
DIS>GPIS>LHBIS for MWD and DIS>LHBIS>GPIS for Agg%, respectively. The
changes in both MWD and Agg% were (15.6; 3.2%) and (-12.3; 4.4%), when both
DIS and LHBIS were compared with GPIS, respectively. Generally, the differences in
both MWD and Agg.% between any two irrigation systems were signifi cant at the 5%
level in the two seasons.
For forming a seed bed with a good tilth, clay soil must be: 1) wetted slowly and 2)
dried thoroughly. Since the GPIS in grapevines is considered furrow irrigation (broad
ridges), the soil is rapidly wetted relative to DIS and LHBIS.
Also in localized irrigation systems, soil is not dried thoroughly before irrigation.
This can lead to aggregates deterioration for the following reasons: 1) ion hydration
and osmotic swelling forces pull water in between clay platelets pushing them apart
and causing swelling of the aggregates; 2) the wetted portion of the aggregates can
swell appreciably compared to the dry one causing a shear plane to accompany the
wetting front which can break many of the bonds; 3) some of the bonding materials
are soluble and dissolve while others are hydratable and may become weaker and more
fl exible as water enters the soil; and 4) displacing the O 2 and N 2 molecules by the more
tightly adsorbed water molecules and joining the air entrapped inside the aggregates
pores leading to increasing pressure, aggregate ruptures and emerging air bubbles.
 
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