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This file contains Figures S1-S10. (PDF 8610 kb)

Twelve, 19.5 acre test plots arranged in a randomized complete block design are set within two 155 acre fields to provide a realistic production environment. These blocks of welldrained Panoche clay loam were formerly irrigated with California Aqueduct water and sprinklers for the last 30 years. Overall the field electrical conductivity (EC) ranged from 0.5 to 4.5, averaging 1.57 dS/m to a 3-foot depth. Saturation extract boron was 0.6 ppm. The area is underlain by a semi-saline aquifer that has been made worse over the decades by contamination from oilfield leachate water. Several production wells were drilled in fall 2003 to begin using this water. A drip tape irrigation system was set up to allow the planting of 6 rows of cotton every 22 feet the first year of the project (2004) followed with the planting of 1 year old pistachio seedling rootstocks March 2005 in 22 foot rows interplanted with 4, 38 inch rows of pima cotton. Salinity of the shallow groundwater for the test fields has varied from 4 to 7.5 dS/m with 8 to 11 ppm B. Three treatments were imposed: AQUEDUCT/CONTROL: EC ~ 0.4 dS/m (Aqueduct water only), BLEND: EC ~ 2.5 dS/m (50/50 mix) and WELL: EC ~ 5 dS/m. Chloride and boron contents in late season cotton petioles and pistachio leaf tissues were significantly higher in the WELL treatment compared to the Control. Saturation extract EC and B in the top three feet of rootzone were significantly increased in the BLEND and WELL treatments over the Control at the end of the season, with most salts increasing significantly to 3 feet with a significant increase in Cl to 5 feet. Cotton yield and tree development: Pima cotton lint yields were nearly 4 bale/acre in 2004, but crashed to about 2 bale/acre in 2005 due to very cool spring conditions that made for poor stand establishment. Cotton yields and plant height were unaffected by salinity. Spring 2006 provided excellent conditions for cotton growth, but excessive salts accumulated in the top 4 inches of the Well treatment beds reduced cotton emergence by 14% (statistically insignificant) and lint yield from the saline Well treatment was reduced by 275 lb/ac compared to the Aqueduct water. However, the Well treatment yield was still excellent at 3.12 bale/ac. Increase in pistachio rootstock diameter and general tree development was unaffected by salinity for both rootstocks for the first three years, but PG1 rootstocks showed a significant 7% decrease at the end of 4th leaf (Figure 1). However, Photoshop® pixel counts of green foliage down the row show an equal amount of green foliage for all treatments as of 10/18/08. Salinity and sustainability: At the end of 2006, after three seasons of cotton irrigation this program applied about 6,600, 32,500 and 54,000 lb/ac of salt in the Aqueduct, Blend and Well treatments, respectively. Rootzone salinity to 5 feet in the wettest part of the profile (between the two hoses) measured by Spring and Fall soil samples has remained surprisingly stable at about an ECe of 2.5 dS/m for the Aqueduct and about 5 to 6 dS/m for the Well treatment. However, in-season ECe in the top two feet is much higher as water and salts sub up from the buried drip tape. Without 6 to 10 inches of effective rainfall or fresh water winter irrigation for efficient leaching this system may not be sustainable. Due to the decrease in cotton yield in 2006, combined with a 50% increase in the Well water EC over the last four years we reduced the salinity of the Well treatment (by blending with Aqueduct water) down to 4.5 dS/m. This is about the salinity of the Well at the start of the test in 2004. After one year of cotton and four years of drip tape irrigation in the pistachios a total of 73,823 lb salt/wetted acre (about a 9.5 foot wide zone of subbing) was applied in the active rootzone of the Well treatment compared to 8,050 lb salt/wetted acre for Aqueduct water. At an average pima price of $1.08/lb, an economic analysis of cotton production and yields for the year prior to and first two years after planting pistachios shows a net return of $2,120 for Aqueduct water @ $120/ac-ft and $2,249 for Well water @ $45/ac-ft for this system.

California Pima cotton production has and been particularly hard hit resulting in acreage declines caused by water supply reductions in the western San Joaquin Valley. Water management methods that improve water use efficiency while maintaining high agronomic yield are of value to the cotton producers that face water supply limitations. We tested structured and predictive approaches to water management and collected field water management information that evaluated our ability to match varying water supply amounts in a way that maximized production and limited economic losses due to reductions in crop quality. Evaluations at four separate sites conducted during the 2005 and 2006 cropping seasons confirmed Pima cotton’s ability to respond favorably to irrigation guidelines recently developed by the UCCE and to modest deficit irrigation approaches that have been developed for Acala type Upland cottons. Variations in soil water storage at each site were large and played a critical role in how Pima cotton responded to in-season water deficits.

The purpose of this research was to determine the magnitude of photorespiration in field-grown cotton (Gossypium hirsutum L.) as a function of environmental and plant-related factors. Photorespiration rates were estimated as the difference between measured gross and net photosynthetic rates.A linear increase in photorespiration was observed as air temperature increased from 22 to 40 degrees C at saturating photon flux density. At 22 degrees C, photorespiration was less than 15 per cent of net photosynthesis and very comparable to the dark respiration rate. At 40 degrees C, photorespiration represented about 50 per cent of net photosynthesis. Gross photosynthesis had a temperature optimum of 32 to 34 degrees C. Water stress, as indicated by Psi(L), did not alter the ratio of gross photosynthesis to net photosynthesis when the confounding effects of leaf temperature differences were accounted for in the data analyses. A reduction in both gross and net photosynthesis was apparent as Psi(L) declined from -2.0 megapascals indicating direct effects of water stress on the photosynthetic process. Photorespiration expressed as a proportion of net photosynthesis increased as water stress intensified.Cotton cultivars possessing a fruit load had significantly higher gross and net photosynthetic rates and lower photorespiration rates than did photoperiod-sensitive cotton strains without a fruit load. Within the fruiting types, which were genetically very similar, only minor differences were observed in the photorespiration:net photosynthesis ratios. However, in the photoperiod-sensitive strains, considerable genetic variability existed when photorespiration was expressed as a proportion of net photosynthesis. These results suggest that the kinetics of ribulose-1,5-bisphosphate carboxylase:oxygenase may be different and, thus, the possibility of genetically reducing photorespiration exists.

The nature of the relationship between photosynthesis and stomatal conductance of 00« was investigated in field-grown cotton (Gossypium hirsutum L.) and sorghum (Sorghum bicolor L. Moench) across growth stages and a range of soil water conditions. The purpose of the study was to determine the degree to which the stomata represent a direct limitation of the photosynthetic process under field environmental conditions. Potential genetic variation in photosynthetic rates, leaf conductances, and photosynthesis:leaf conductance ratios was investigated in 14 strains of cotton and in 20 lines and 9 hybrids of sorghum under both irrigated and dryland conditions. The results of the research provide insight into the potential for genetically increasing C0« fixation without concurrently increasing water loss. Diurnal and seasonal observations made across numerous strains of cotton indicated that gross photosynthetic rates were related to stomatal conductances of upper canopy leaves in a curvilinear rather than a strictly linear manner. Increases in leaf conductance of CO^ in excess of 0.8 to 1.2 cm s" did not result in consistent increases in gross photosynthetic rates. Increases in external C0« concentration to levels above ambient did not produce consistent increases in photosynthetic rates even though intercellular COp availability increased. These results indicate that factors in addition to stomatal control of CO^ diffusion are involved in determining photosynthetic rates of cotton. A more nearly linear photosynthesis: conductance relationship was observed in sorghum, but observed photosynthesis and conductance levels were poorly correlated on a long term basis. Data collected across the entire season and including all lines and hybrids resulted in low coefficients of determination (r) for the photosynthesis: conductance relationship, generally less than 0.3. A portion of the variability in the longterm relationship between photosynthesis and conductance was associated with the influence of growth stage and moderate to severe water stress on the photosynthesis:conductance relationship. Pooling across all genotypes, photosynthesis:conductance ratios were generally lower during grain filling than prior to flowering, and also declined with moderate to severe water stress. In both crop species, measurements were made throughout both vegetative and reproductive growth stages to evaluate the consistency of genetic ranking in each parameter. On all sampling dates, significant variation existed among strains within each species for gross photosynthesis, leaf conductance, and photosynthesis per unit leaf conductance. Variation in these parameters was evident among cotton strains, but conductance levels were more variable than photosynthetic rates, In contrast, considerable genetic variability was evident in both photosynthesis and conductance among sorghum lines and hybrids. Particularly in some strains of sorghum, the relative genetic ranking of photosynthesis and leaf conductance was variable both with irrigation treatment and growth stage. However, individual entries were identified which exhibited consistently high photosynthetic rates and photosynthesis: conductance ratios over a considerable portion of the season. The large genetic variability in photosynthesis, conductance, and. photosynthesis:conductance ratios identified a viable approach toward genetic improvement of photosynthetic productivity and water use efficiency in cotton and sorghum.