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ON.PA t-
<br /> 4 6
<br /> 3'5 I -- Inlet
<br /> N — Top basin
<br /> 3':0 - Middle basing
<br /> 2:5 — Bottom basin
<br /> rptth
<br /> ul
<br /> bottom basin
<br /> 1 r st
<br /> 1.0}
<br /> Fig.3.Electrical conductivity of rice field water at
<br /> "' 2:1 the inlet,top,middle and bottom basins from a
<br /> Ur m
<br /> salt-affected field intensively monitored in 1995.
<br /> The water holding period can substantially
<br /> increase salinity in the bottom basin.
<br /> vexr:.�xa5s�gaeu� tta .. �t
<br /> salinity increases in bottom or lower yield (r=0.29).At this site, poor weed Coping with salinity
<br /> basins to some degree in most fields control in the top basin had likely af- Rice growers have made great
<br /> during the water holding period (data fected yield more than salinity in the strides in reducing pesticide loads into
<br /> not shown).They also showed that dif- bottom basin, thereby reducing the rivers by holding water on fields longer
<br /> ferent irrigation systems influence field salinity-yield correlation.At a second and using various alternative irrigation
<br /> water salinity patterns (fig.4A-13). In location with lower salinity levels but a systems. At the same time,increased
<br /> conventional systems salinity levels in- similar salinity range,stands (r=-0.22) soil and water salinity levels,particu-
<br /> c:reased from top to lower basins.In and yields (r=-0.30)were negatively larly in bottom basins,have been asso-
<br /> static systems each basin was irrigated correlated with ECI`w during the water ciated with reduced rice stands and
<br /> independently,and salinity levels holding period. yield. Higher salinity in bottom basins
<br /> among basins varied somewhat but
<br /> were not significantly different. How y,
<br /> ever, in both systems salinity increased
<br /> with distance from the water inlet.The a <
<br /> soil salinity and water flow patterns may
<br /> contribute to spatial variation between
<br /> and among basins in the static irrigation
<br /> systems.After the water holding period, p, i } ,°ert ('�rir ° t ` I': a �Isper Miabie tower
<br /> differences among and within basins
<br /> a a ',txrc��` s ..1 1 v r�,q�,�w,m7_• �..�S.Fk LX H � � �.�d� � +#s .-�.
<br /> declined sharply.ECfw levels increased
<br /> during the water holding period,but
<br /> decreased later when irrigation water Early.'WH 1,a;DA'p s Early WHP, 14 DAP
<br /> was again added to the field.
<br /> l 0.10-0.49
<br /> In the static system,the measured
<br /> peak EC,,.occurred at the middle of the 0.50-0.99 9,
<br /> water holding period—water was 1.00-1.99
<br /> added just prior to the late sample time, " " "' "'
<br /> Late WHP,36 DAP
<br /> «:.. , t -1 -2.99
<br /> most likely lowering the EC level. Al r °"�I } 2.00
<br /> , x'
<br /> F
<br /> though not illustrated in figure 4,data 3.00-3.99
<br /> from earlier studies showed increases
<br /> ,�� , f^
<br /> in late-season ECf levels in static and 4.00-4.99
<br /> other closed-basin systems.The mean 5.00-5.99
<br /> EC,(51 samples) for all basins was 3.1
<br /> x {
<br /> dS/m in the conventional and 1.7 dS/
<br /> m in the static system.
<br /> Yield data from the 1997 field study c 45 " a •'
<br /> was inconsistent.EC at one location, t�� anvr ,fr�;
<br /> which ranged from less than 1 dS/m y�� ?' tt' #� '��} f` ` `�P° i' fvllddl'e tower
<br /> to greater than 4.0 dS/m at the end of
<br /> +nrv. 7A1
<br /> the water holding period,was nega- WHP Water holding period DAP Days after planting Al. Water flow ... water outlet blocked•
<br /> tively correlated with reduced stand ; water outflow
<br /> r .�nr~,+:�:t�r nrsxnc�raawwst.udreaeurwtrrra.+:r�a+rs.aepr�aw,M1..a.,4vare+.ter..„.,.,.wa�c.wF ti� �rrr,.., �,. ...:.. ,
<br /> (r=-0.38,mean water holding period Fig.4.Field-water electrical conductivity patterns in rice fields with(A)conventional and
<br /> ECt,, versus stand density),but not to (B)static irrigation systems,at three monitoring times after planting.
<br /> httlY//danr.ucop.edu/calag NOVEMBER DECEMBEI?2002 187
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