SU0006554 SSCRPT - Laserfiche WebLink

Home Browse Search

e growing areas. In the early 1990s some 1993 � , , rice growers noticed problems with " ,^t U stand establishment in parts of their ■ 199q "k r. ? fields.They suggested that salinity + problems might develop with the 995 longer water holding periods and/or in closed irrigation systems.The late- season no-spill policy was discontinued in 1995,and other less restrictive modi- fications have been made since. Rice is sensitive to salinity,particu- larly during the early seedling (Maas 1990) and pollination stages (Khatun and Flowers 1995).Salinity stress dur- ing these periods may reduce ricemaw growth and/or yield.In rice,salinity during the seedling stage causes a re tr n r 'ti 5;itt ' fly` 'r sltir duction in stand density and seedling biomass (Shannon et al. 1998). During Fig.1.Electrical conductivity among district(D)and nondistrict(ND) irrigation water pollination salinity may cause panicle sources in Glenn and Colusa counties.(Readers may e-mail srgrattoncaucdavis.edu for blanking (sterile florets) or sterility, identities of district and nondistrict irrigation water sources.) leading to a reduction in grain yield. conductance of the water supply,which these fields varied considerably,as has Rice is more tolerant of salinity at other is related to its saltiness.) been previously described (Hill et al. growth stages,and salinity stress dur- Irrigation districts that divert water 1995). Salinity of the water was moni- ing these periods has less impact on from the Sacramento River had the tored at the inlet., top and bottom ba- yield (see Grattan et al.,p. 189). lowest mean summertime salinity lev- sins of each field in June,July and We initiated salinity investigations els (0.13 to 0.31 dS/m).Other district August.The June sample time was in the early 1990s to determine if salin- and nondistrict sources had low but during or close to the water holding ity was adversely affecting rice produc- slightly higher mean summertime sa- period in many of the fields studied. tion in California and to determine linity levels (0.40 to 0.54 dS/m). Soil salinity was also monitored in impacts on yield.Different irrigation Nondistrict water sources that used a these fields at the same times but was systems that limit the discharge of field mixture of drain and well water had not initiated until midway through water into waterways were monitored higher mean salinity levels (0.62 to 1.47 the 1993 season. Some fields utilized to evaluate the distribution of salinity dS/m). Drain water from nonrice field recirculating,gravity or static systems within particular fields. sources may have also affected water to manage water during the water quality at some sites. holding period while others held wa- Irrigation water salinity The mean summertime EC.for all ter for the required holding period or Thirteen irrigation district and irrigation water sources was highest in season-long. Yield data was collected nondistrict water sources in Colusa and 1994 and lowest in 1993 and 1.995.For in 1994 and 1995 from 3.3-feet-by-3.3- Glenn counties were monitored for sa- example, the mean salinity level in the feet (1 square meter) plots near the sa- linity in June.July and August from Colusa Basin Drain at the Davis Weir linity monitoring locations in each of 1993 through 1995. District water was 1.22 dS/m in 1994,but only 0.73 the top and bottom basins. comes directly from an irrigation and 0.75 dS/m in 1993 and 1995,re- Mean bottom-basin water salinity agency such as the Glenn-Colusa Irriga- spectively.The higher salinity levels in levels were significantly higher than tion District,while nondistrict water 1994 (compared to 1995) can likely be those in top basins,while EC of the in- provides a mix of river water,well wa- attributed to higher cumulative evapo- let water was often the same as EC of tet-and/or recaptured drain water. transpiration (ET) and lower rainfall the field water (EC,.) in the top basin Data indicated that most irrigation wa- during the summer (June to August) (fig.2).Fields with low EC,,levels ters had low mean surnmertime salin- months, in addition to stricter water showed little difference between top ity levels. For example, the electrical conservation practices. and bottom basins. conductivity of the inflow water Data for June is presented because (EC j —which goes up as water Field salinity monitoring the water salinity levels were higher salinity increases—was less than We also monitored 27 rice fields that and the differences between the top 0.7 deciSiernens/meter (dS/m), but used conventional,recirculating and and bottom basins were greater during some sources had moderate levels of gravity irrigation systems for salinity in or after the water holding period.The 0.7 to 1.47 dS/m (fig. 1). (DeciSiemens Colusa and Glenn counties,annually salinity level and relative differences per meter is a measure of the electrical from 1993 to 1995.Management of between top and bottom basins de- http://danr.ucop.edu/calag NOVEMBER-DECEMBER 2002 185