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In an effort to elucidate the physiological processes involved in cowpea differential growth response of four major USA cowpea cultivars (CB5, CB27, 8517 and 7964) to increasing salinity, we investigated the effect of salinity on leaf gas exchange of net photosynthetic rate per unit leafmass(Pnm)andperunitleafarea(Pna),andstomatalconductance(gs)ofthefourcowpeacultivars.Theexperimentwassetupasastandard split-plot design in which cowpea plants were grown in greenhouse sand tanks irrigated with nutrient solutions. Seven salinities ranging from 2.6 to 20.5 dS m � 1 were constructed based on Colorado River water salt composition with NaCl, CaCl2 and MgSO4 as the salinization salts. Light-saturated Pnm, Pna and gs of fully expanded trifoliage were examined at the vegetative growth and flowering stages, and the data were analyzed using a split-plot analysis of variance (ANOVA) model. We found a highly significant (P � 0.0001) reduction of Pnm, Pna and gs due to salinity. The responses of Pnm, Pna and gs to salinity could be further described by a general model of log(y )= a1 + a2x + a3x 2 ,w herey represents either Pnm, Pna, or gs; a1, a2 and a3, empirical constants; x, salinity. We found that Pnm was more sensitive to salinity than Pna. Additionally, we found that increasing stomatal closure with increasing salinity might limit Pnm or Pna. While we did not find any significant difference (P > 0.05) of Pnm and Pna among the four cultivars, we did find a significant difference (P � 0.05) in gs. No significant

Over the last several years, there has been increasing interest in amending the soil using cover crops, especially in desert agriculture. One cover crop of interest in the desert Coachella Valley of California is cowpea [Vigna unguiculata (L.) Walp.]. Cowpea is particularly useful in that as an excellent cover crop, fixing abundant amounts of nitrogen which can reduce fertilizer costs. However, soil salinity problems are of increasing concern in the Coachella Valley of California where the Colorado River water is a major source of irrigation water. Unfortunately, little information is available on the response of cowpea growth to salt stress. Thus, we investigated the growth response of 12 major cowpea cultivars (`CB5', `CB27', `CB46', `IT89KD-288', `IT93K-503-1', `Iron Clay', `Speckled Purple Hall', `UCR 134', `UCR 671', `UCR 730', `8517', and `7964') to increasing salinity levels. The experiment was set up as a standard Split Plot design. Seven salinity levels ranging from 2.6 to 20.1 dS·m–1 were constructed, based on Colorado River water salt composition, to have NaCl, CaCl2 and MgSO4 as the salinization salts. The osmotic potential ranged from –0.075 to –0.82 MPa. Salt stress began 7 days after planting by adding the salts into irrigating nutrient solution and ended after 5 consecutive days. The plants were harvested during flowering period for biomass measurement (53 days after planting). Data analysis using SAS analysis of variance indicated that the salinity in the range between 2.6 and 20.1 dS·m–1 significantly reduced leaf area, leaf dry weight, stem dry weight and root dry weight (P ≤ 0.05). We applied the data to a salt-tolerance model, log(Y) = a1 + a2X + a3X2, where Y represents biomass, a1, a2 and a3 are empirical constants, and X represents salinity, and found that the model accounted for 99%, 97%, 96%, 99%, and 96% of salt effect for cowpea shoot, leaf area, leaf dry weight, stem dry weight and root dry weight, respectively. We also found significant differences (P ≤ 0.05) of each biomass parameter among the 12 cultivars and obtained different sets of the empirical constants to quantitatively describe the response of each biomass parameter to salinity for individual cowpea cultivars. Since a significant salt × cultivar interaction effect (P ≤ 0.05) was found on leaf area and leaf dry weight, we concluded that salt tolerance differences exist among the tested cultivars.

Soybean is an important crop worldwide. Soybean cultivars differ in their sensitivity to soil salinity and herbicide damage. In these experiments, we examined the impact of salinization an...

An assessment of field-scale variation and the characterization of correlated crop response are the first steps in evaluating the potential for variable-rate technologies and other techniques used in site-specific management (SSM). The responses of sugar beets to salinity and to residual and applied soil N were studied at sites in California's Imperial and San Joaquin Valleys to evaluate the potential of electromagnetic induction (EMI) techniques for SSM. Electromagnetic induction was used to create geo-referenced assessments of apparent soil electrical conductivity (EC"a) and correlated soil properties in salt-affected fields in the Imperial (IV) and San Joaquin (SJV) Valleys. Soils at the two sites were primarily fine, smectitic (calcareous) thermic, vertic Torifluvents and Fluvequents, respectively. Two crops were grown in the IV and one in the SJV. Root and gross sugar yields were evaluated at field scale using a yield monitor and in subplots centered on soil sampling locations chosen using ESAP-95 (v. 2.01) software that were harvested by hand. Average subplot root yields differed from field-scale averages derived from the yield monitor by less than 4% for all three crops. In the IV field, average salinity increased with depth, indicating leaching of salts. The natural logs of electrical conductivity of the saturation paste extract (EC"e) and saturation percentage (SP) were strongly correlated with measured EC"a (r=0.97 and r=0.86, respectively) and nitrate was moderately correlated (r=0.55). Root and sugar yields declined at the higher salinity levels from 18.0 to 8.0mgha^-^1. The SJV site was poorly drained and leaching was not apparent. EC"e was strongly correlated with EC"a (r=0.94), but SP was not (r=0.20). Gross sugar yields apparently were influenced by SP rather than by EC"e and varied from 2.9 to 14.1mgha^-^1. Where crop growth and yield are influenced by salinity, EMI is useful for estimating optimum fertilizer N application rates and for identifying areas of the field that will have unprofitable yields. Irrigation might be withheld from these areas and the water saved for other beneficial uses.

Greenhouse experiments were conducted to determine the effect of salinity, imazethapyr, and chlorimuron on weed growth. Five species, barnyardgrass, common cocklebur, ivyleaf morningglory, common purslane, and yellow nutsedge, were grown in potting soil and irrigated with nonsaline (EC ∼ 2 dS m−1) or sulfate-dominated saline (EC ∼ 7 dS m−1) nutrient solution. Plants were treated after emergence with imazethapyr (Pursuit formulation) at 70 g ae ha−1 or chlorimuron ethyl (Classic formulation) at 8.8 g ai ha−1. Results indicated that irrigation with saline water had no overall effect on the growth or survival of most tested weed species. Growth of yellow nutsedge (maximum height and stem diameter) was reduced for plants irrigated with saline water. Observed growth and survival trends in saline and nonsaline treatments were consistent with information on the herbicide label. Complete control of common purslane was not achieved by either chlorimuron or imazethapyr. Growth and survival of ivyleaf morni...

Due in large measure to the prodigious research efforts of Rhoades and his colleagues at the George E. Brown, Jr., Salinity Laboratory over the past two decades, soil electrical conductivity (EC), measured using electrical resistivity and electromagnetic induction (EM), is among the most useful and easily obtained spatial properties of soil that influences crop productivity. As a result, soil EC has become one of the most frequently used measurements to characterize field variability for application to precision agriculture. The value of spatial measurements of soil EC to precision agriculture is widely acknowledged, but soil EC is still often misunderstood and misinterpreted. To help clarify misconceptions, a general overview of the application of soil EC to precision agriculture is presented. The following areas are discussed with particular emphasis on spatial EC measurements: a brief history of the measurement of soil salinity with EC, the basic theories and principles of the soil EC measurement and what it actually measures, an overview of the measurement of soil salinity with various EC measurement techniques and equipment (specifically, electrical resistivity with the Wenner array and EM), examples of spatial EC surveys and their interpretation, applications and value of spatial measurements of soil EC to precision agriculture, and current and future developments. Precision agriculture is an outgrowth of technological developments, such as the soil EC measurement, which facilitate a spatial understanding of soil-water-plant relationships. The future of precision agriculture rests on the reliability, reproducibility, and understanding of these technologies.

Crop yield inconsistently correlates with apparent soil electrical conductivity (EC a ) because of the influence of soil properties (e.g., salinity, water content, texture, etc.) that may or may not influence yield within a particular field and because of a temporal component of yield variability that is poorly captured by a state variable such as EC a . Nevertheless, in instances where yield correlates with EC., maps of EC, are useful for devising soil sampling schemes to identify soil properties influencing yield within a fleld. A west side San Joaquin Valley field (32A ha) was used to demonstrate how spatial distributions of EC a can guide a soil sample design to determine the soil properties influencing seed cotton (Gossypium hirsutum L.; 'MAXXA' variety) yield. Soil sample sites were selected with a statistical sample design utilizing spatial EC, measurements. Statistical results are presented from correlation and regression analyses between cotton yield and the properties of pH, B, NO 3 -N, Cl - , salinity, leaching fraction (LF), gravimetric water content, bulk density, percentage clay, and saturation percentage. Correlation coefficients of -0.01, 0.50, -0.03, 0.25, 0.53, -0.49, 0.42, -0.29, 0.36, and 0.38, respectively, were determined. A site-specific response model of cotton yield was developed based on ordinary least squares regression analysis and adjusted for spatial autocorrelation using maximum likelihood. The response model indicated that salinity, plant-available water, LF, and pH were the most significant soil properties influencing cotton yield at the study site. The correlations and response model provide valuable information for site-specific management.

The correlation structure between apparent soil electrical conductivity (EC a ) and various soil properties can often appear radically dissimilar in different field surveys. Ideally, some type of methodology for survey data validation should be developed that can predict the expected correlation structure between EC, survey data and various soil properties, given information about the soil properties themselves. In this paper, we review an existing model for EC a and hypothesize that this model can be used to accurately predict the expected correlation structure between EC, data and multiple soil properties of interest (such as soil salinity, saturation-paste percentage, and soil water content). Our objective is twofold: (i) to demonstrate how this model can be employed to produce the expected correlation structure and (ii) to extend this EC, model to handle survey data collected under low water content situations by dynamically adjusting the model's assumed water content function. This adjustment can be estimated using acquired EC, signal and soil sample data, and its statistical significance can be determined for each specific survey situation. We demonstrate both of these techniques using acquired electromagnetic induction signal data and measured soil properties of interest from 12 different field salinity surveys performed in California and Colorado and in Alberta, Canada. Results from these 12 surveys suggest that the ordinary model is able to accurately predict the expected correlation structure between conductivity and soil property when the water content is near field capacity and that the dynamically adjusted model is able to substantially improve the accuracy of the predicted correlation structure when the water content is significantly below field capacity.

Depth of standing water in rice paddy fields is an important agronomic parameter in the management of irrigation-related salinity problems. It was hypothesized that reductions in the yield of rice under salinity stress can be ameliorated by adjusting the water depth. This study was designed to determine the interactive effects of salinity and water depth on seedling establishment and grain yield in rice. Plants were grown in a greenhouse and irrigated with nutrient solutions amended with NaCl and CaCl2 (5:1 molar concentrations). Treatments were three salt levels with electrical conductivities at 0.9, 3.3 and 6.0 dS m−1 and six water depths at 4, 7, 10, 13, 16 and 20 cm. The effects of both salinity and water depth were significant on plant growth and yield. However, there was no interaction between the effects of salinity and water depth. Reductions in seedling establishment and grain yield with increases of salinity and water depth resulted from a simple combination of the two different stresses on plants. Highly significant negative correlations were identified between water depth and seedling establishment and also between water depth and grain yield when data were combined across salt levels. Generally, plants performed better with respect to seedling establishment and grain yield in shallow water (i.e. 10 cm). Under salt stress, the effect of water depth was significant for panicle number, but not significant for panicle weight. The loss of grain yield under salt stress with the increases of water depth was mainly due to reduction in fertile tiller number. We suggest that water depth be lowered during the initiation and growth of productive tillers. However, the practice by lowering water depth must be incorporated with appropriate field management such as the increase of irrigation frequency, precision leveling, and effective weed control methods.

Management options for reducing drainage water volumes on the west side of the San Joaquin Valley of California, such as reuse of saline drainage water and water table control, have the potential to adversely impact crop yields due to a build up in soil solution boron concentration. An earlier experiment had shown that extrapolation of B soil tests to field conditions provided poor predictability of B content of melons despite statistically significant relationships. Consequently, three tests for extractable soil B were evaluated for their ability to predict conditions of potential B toxicity in melons grown under controlled conditions. Melons were grown for 95 days in two consecutive years in containers of Lillis soil (very-fine, smectitic, thermic Halic Haploxerert) that had been pretreated with solutions containing B concentrations as great as 5.3 mmol L −1 . Extractable soil B was determined using ammonium acetate, DTPA-sorbitol, and a 1:1 aqueous soil extract at the beginning and end of the experiment. The B treatments caused various deleterious effects on melon growth and development. Fresh and dry plant matter decreased significantly with increasing B concentrations, while B concentration of plant leaves, stems, and fruits increased significantly with increasing B. The number of days to first flowering was significantly delayed from 35 days at B treatments 3 mmol L −1 . Fruit set was completely inhibited at the highest B treatment of 5.3 mmol L −1 . Plant analysis revealed a highly significant relationship between soil extract B obtained with all three extractants and leaf, stem, and fruit B content. Correlation coefficients for plant stems and fruits were much higher than for plant leaves. Correlation coefficients for all soil tests were almost equivalent, although the highest values were obtained for the DTPA-sorbitol extract indicating the greatest predictive capability. The soil tests were well able to predict B damage to melons in a container experiment.

Differential sensitivity during growth stages is one of the major issues in the management of saline water for irrigation. This study was designed to analyze the effects of salinity on plant growth and yield components of rice by composing 20-day periods of salinization at different growth stages. Plants were grown in sand tanks in a greenhouse and irrigated with nutrient solutions. Treatments were three levels of salinity with electrical conductivities at 1.8, 3.2 and 4.6 dS m−1 and five timing treatments. Plants were salinized on the day of seeding, 1-leaf, 3-leaf, panicle initiation (PI), and booting stages, respectively, and stress was relieved after 20 days in each timing treatment. Salinity-induced reductions in shoot dry weights of plants harvested before PI were significant, but there were no significant differences among timing treatments. Reduction in shoot dry weight of plants harvested at seed maturity was significant only when plants were salinized for a 20-day duration before booting, but not after booting. Reduction in tiller number per plant was significant only when plants were salinized for a 20-day duration before PI. The reductions in spikelets per panicle and seed weight per panicle were most pronounced when plants were stressed between the 3-leaf and PI stages or between PI and booting stages and minor when stressed at the other stages. A 20-day period between 3-leaf and PI stages was most sensitive to salinity in terms of seed yield. These results indicate that the differential sensitivity at growth stages can be clearly shown when stages are well defined in the timing treatments and the stress is quantified at growth stages based on the same duration of salinization. The interaction between cultivar and timing treatment was not significant. Uniform management options can be developed for irrigation using saline water for the cultivars with similar genetic backgrounds.

ADDITIONAL INDEX WORDS. salinity, salt stress, water reuse, irrigation water, drainage water ABSTRACT. Saline agricultural drainage water may be used as a resource to grow high value horticultural crops and reduce the volume of drainage for eventual disposal. To explore reuse options the effects of salinity and timing of application were tested on selected leafy vegetables grown in 24 sand culture plots in Riverside, Calif. The leafy winter vegetables included 'Ruby Red Chard' Swiss chard ( Beta vulgaris L. var. flavescens (Lam.) Lam.), 'Space' spinach ( Spinacia oleracea L.), 'Vitamin Green' salad greens ( Brassica rapa L. (Narinosa Group)), 'Red Giant' mustard greens ( Brassica juncea L. (Czerniak)), pac choi (Brassica rapa L. (Chinensis Group)), 'Winterbor' kale ( Brassica oleracea L. (Acephala Group)), tatsoi (Brassica rapa L. (Narinosa Group)), 'Salad King' curly endive ( Cichorium endivia L.), and 'Red Preco No. 1' radicchio (Cichorium intybus L.). All vegetables were planted at the same time and irrigated initially with tap water and nutrients. At 3 and 7 weeks after seeding (application times), six salinity treatments were initiated by adding salts to the irrigation water to represent the chemical compositions of drainage waters found typically in the San Joaquin Valley, Calif. The six salinity treatments had electrical conductivities of 3 (control), 7, 11, 15, 19, or 23 dS·m -1 . A randomized complete block design was used with (6 salinities × 2 application times × 2 replications). Within each plot a 1.5-m row of each of the nine vegetables was grown as split plots. Salinity reduced fresh weight (FW) yields of all species. Salt stress applied at 3 weeks after seeding reduced FWs for seven of the nine vegetables compared to salination at 7 weeks. Analyses of salt tolerance curves, maximum yields, and the point of 50% yield reduction (C 50) were conducted. Greens produced the highest biomass at 874 g/plant, but was the most affected by application time. Swiss chard and radicchio were not significantly affected by timing of salinity application, and Swiss chard was the most salt tolerant overall. Greens, kale, pac choi, and to a lesser extent, tatsoi, have potential as winter-grown, leafy vegetables in drainage water reuse systems. markets. Potential crops include winter vegetables, flowers, herbs, medicinals, and other species that are tolerant to drainage water irrigation and would provide high economic return (Shan- non and Grieve, 1999, 2000). In this study, we used synthetic drainage water with ion composition similar to that found typically in the San Joaquin Valley to irrigate nine leafy winter vegetables. The purpose of the study was to determine potential yield and salt tolerance over a range of salinities and to determine if improved yields could be obtained if initial salination were delayed past the early plant establishment stage in which most plants are considered to be salt sensitive (Shannon et al., 1994).

Perchlorate (ClO₄⁻) has been detected in edible leafy vegetables irrigated with Colorado River water. The primary concern has been the ClO₄⁻ concentration in lettuce (Lactuca sativa L. var. capitata L.). There has been a limited number of studies on ClO₄⁻ uptake, but the interactive effect of other anions on ClO₄⁻ uptake is not known in detail. We conducted a greenhouse ClO₄⁻ uptake experiment using two types of lettuce (iceberg and butterhead) to investigate the interaction of uptake of ClO₄⁻, Cl⁻, and NO₃⁻ on ClO₄⁻ uptake under controlled conditions. We examined three concentrations of ClO₄⁻, 40, 220, and 400 nmolc/L; Cl⁻ at 2.5, 13.75, and 25 mmolc/L; and NO₃⁻ at 2, 11, and 20 mmolc/L. Perchlorate was taken up the most in lettuce when ClO₄⁻ was the greatest and NO₃⁻ and Cl⁻ were lowest in concentration in the irrigation water. More ClO₄⁻ was detected in leafy material than in root tissue. In general, the outer leaves of iceberg and butterhead lettuce contained more ClO₄⁻ than did the inner leaves. The results indicate that selective ClO₄⁻ uptake occurs for green leaf lettuce. A predictive model was developed to describe the ClO₄⁻ concentration in lettuce as related to the Cl⁻, NO₃⁻, and ClO₄⁻ concentration in the irrigation water. Research results can be utilized to elucidate the effect of salts on the accumulation and uptake of ClO₄⁻ by edible leafy vegetables.

Grain yield in wheat (Triticum aestivum L. emend. Thell.) is highly dependent upon the number of spike-hearing tillers produced by each plant. Soil salinity can greatly decrease their number and productivity. Knowing the contribution of specific tillers is essential for breeding salt-tolerant genotypes and for developing wheat growth simulation models. Our objective was to determine the effects of soil salinity on the contribution of individual cuhns to total grain and dry matter yields of two spring wheat cultivars, Anza and Yecora Rojo. Plants were grown in Pacbappa fine sandy loam soil (mixed, thermic, Mollic Haploxeralf) in outdoor lysimeters for 2 yr. Three salinity treatments were imposed by irrigating with waters containing equal weights of NaCl and CaClr (electrical conductivities z 1, 12, or 18 dS m-r). Despite substantial losses in the number of tillers at moderate levels of salt stress, grain yields of the main stem (MS) and tillers Tl and T2 were as great or greater than those on nonstressed plants of both cultivars. The contribution of the MS to yield on a land area basis increased from about 25 to 35% in nonsaline treatments to over 80% with increasing salinity. The contribution of primary tillers (E 5865% in nonsaline conditions) decreased substantially only at the highest salinity levels. Salinity stress significantly decreased the number of spikelets per spike but the number of kernels per spike either increased or was unaffected except at the highest level of stress. Increasing salinity decreased total straw yields primarily because of fewer tillers, but dry weights of the MSs and remaining tillers were also smaller. Results show that loss of spike-bearing tillers accounts for most of the yield reduction in salt-stressed wheat.

Wheat (Triticum aestivum L. emend. Thell.) grain yields are highly dependent upon the number of spike-bearing tillers produced per plant. Salinity, drought, and other environmental stresses can greatly affect the development and viability of tillers. We determined the effects of soil salinity on the occurrence and rate of tiller development and the incidence of tiller abortion in spring wheat cultivars, Anza and Yecora Rojo. Plants were grown in Pachappa fine sandy loam soil (mixed, thermic, Mollic Haploxeralf) in outdoor lysimeters. Three salinity treatments were imposed by irrigating with waters containing equal weights of NaCl and CaCl 2 (electrical conductivities of ≃ 1, 12, or 18 dS m −1 ). Salinity significantly decreased the number of primary and secondary tillers in both cultivars [...]

Salt tolerance of wheat (Triticum aestivum L.) is known to change during different stages of growth. The effects of salinity on growth and yield components of wheat at different stages of growth were determined in a 2-yr field plot study at Brawley, CA. Four salinity levels were imposed on a Holtville silty clay [clayey over loamy, montmorillonitic (calcareous), hyperthermic Typic Torrifluvent] by irrigating with waters salinized with NaCl and CaCl 2 (1:1 w/w). Electrical conductvities of the irrigation waters were 1.4, 10.0, 20.0, and 30.0 dS m −1 in 1989), and 1.4, 8.0, 16.0, and 24.0 dS m −1 in 1990. The three irrigation treatments were (i) salinity imposed throughout the growing season, (ii) szaline irrigation initiated after terminal spikelet differentiation (TSD), and (iii) saline irrigation discontinued at TSD [...]

Grain development in wheat (Triticum aestivum L.) is a complex process tha tresponds to interactions among primary genotypic factors and the environment. This study was conducted to determine the effects of salinity stress on kernel occurence and kernel mass distributions within the main spike. Mexican semidwarf wheat cultivars Yecora Rojo and Anza were grown in sand tanks in the greenhouse with saline and nonsaline nutrient solutions. At harvest, each spikelet position and grain position was identified and the weight of every kernel was determined (...)

Grain yield potential of wheat (Triticum aestivum L.) main spikes is genetically determined and depends upon the number of spikelets per spike, the number of kernels per spikelet, and the weight of individual kernels. Environmental factors may interact with the genotype to influence the expression of these components. This study was initiated to determine the effects of salinity on main-spike yield components of two Mexican semidwarf, hard red spring wheat cultivars, Yecora Rojo and Anza (...)