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,
<br /> a
<br /> N y
<br /> M Inlet ECS„ i'
<br /> 3 s
<br /> 4 0 Top basin ECS,,, 5
<br /> a>. 4�s 'F a We u {ai 3
<br /> ® Bottom Bottbasin EC 1R (°
<br /> fw a �r3uS
<br /> 1yp e 1 :!x{Yt A � ,a 14v1 ii � t,fr r4 fq 1 r
<br /> v
<br /> W ;
<br /> a br, `. 1 " n
<br /> 1 3 ave 1Y'i �+ i I�r l*f 25 mmm
<br /> 27
<br /> r i sf Y, xlV4 Id ^�
<br /> Fig.2.Electrical conductivity of water at field inlet(EC.)and in field water(EC,)in top and bottom basins
<br /> from 27 rice fields in Colusa and Glenn counties,June 1995.
<br /> clined later in the season after water the water holding period, particularly without experiencing stand problems
<br /> flow and depths increased. Similar re- in bottom basins. Conversely,the low and yield losses.
<br /> sults were observed with soil EC (data salinity field,which held water season- Multiyear analysis of yield data indi-
<br /> not shown). Frorn 1993 through 1995, long, had low salinity levels all season cates a significant decrease in grain in
<br /> the mean ECr1,for June was 0.70 dS/m (0.1 to 0.2 dS/m), bottom basins compared to top basins
<br /> in the top basins and 1.28 dS/m in the In one of the high-salinity fields, the (9,700 versus 10,300 pounds/acre).
<br /> bottom basins of all fields monitored. EC of inlet water (ECj was similar to Single-year analysis indicates that top
<br /> Similar patterns were found in 1994.In that in the top basin,regardless of time and bottom basin yields were signifi-
<br /> fields with higher salinity levels, rice after flooding (fig. 3). During the water cantly different in 1994 but not in 1995
<br /> stand establishment was affected more holding period,water salinity levels in (10,960 versus 9,880 pounds/acre,re-
<br /> in bottom basins than top basins, the bottom basin increased rapidly, spectively).The absence of yield de-
<br /> In 1994,during the June sample, which we attribute to a combination of cline in 1995 was probably due to lower
<br /> field water and soil salinity levels corre- no outflow,reduced inflow rates and EC levels in some irrigation water
<br /> lated significantly in both top and bottom evapoconcentration of salts.This sug- sources,lower cumulative ET during
<br /> basins(r'=0.52 and rz=0.70,respec- gests salinity can be a serious problem the season and lower salinity levels in a
<br /> tively),The relationship between ECTµ, in some fields during the water holding number of rice fields.Grattan et al. (see
<br /> and the average root-zone salinity(EC) period. However,adding fresh water p. 189) subsequently conducted con-
<br /> varied between top and bottom basins (lower EC) to the bottom basin toward trolled studies to better understand and
<br /> and at different times during the season. the end of the holding period increased quantify the relationship between salin-
<br /> In 1995,water salinity was moni- the field's water level and reduced sa- ity,crop performance and yield.
<br /> tored more frequently in several fields, linity, indicating that monitoring and
<br /> two with high salinity and one with management can help moderate a salin- Impact of irrigation systems
<br /> lower salinity.Salinity data was similar ity problem. In bottom basins of some In 1997,extensive sampling was con-
<br /> in both fields with the highest salinity, fields,salinity increases made it diffi- ducted in six rice fields to compare dif-
<br /> indicating that EC, was highest during cult for some growers to hold water ferent irrigation systems and determine
<br /> what influence they have on salinity
<br /> patterns in the field. In the conven-
<br /> tional.system, water flows in series
<br /> ,7w from basin to basin while in the static
<br /> system water is independently deliv-
<br /> ered to each basin from a supply/
<br /> drain ditch perpendicular to the ba-
<br /> sins. Flap-gated pipes prevent water
<br /> i; mixing between basins. Seventeen lo-
<br /> cations were monitored in each of an
<br /> upper, middle and lower basin in
<br /> each field (51 samples per field). At all
<br /> locations, field water salinity was mea-
<br /> sured throughout the season and soil
<br /> i' salinity was measured at harvest. At
<br /> two sites,soil salinity was measured at
<br /> Appropriate water management in fields can help to reduce salinity damage and produce rrridseason and yields at harvest.
<br /> a healthier rice crop.This normal rice, above,was irrigated with water at 0.6 dS/m,well
<br /> below the threshold for salinity stress. These studies confirmed that water
<br /> 186 CALIFORNIA AGRICULTURE,VOLUME 56,NUMBER 6
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