Abstracts

Foderaro, M. and Ungar, I. 1997, 'Growth and Survival of Polygonum aviculare L. at a Brine-contaminated Site in Southeastern Ohio', American Midlands Naturalist, vol. 138, pp. 140-152.

Populations of Polygonum aviculare from low-salinity and high-salinity sites at a brine spill location in Ohio were studied to determine the effects of edaphic factors and intraspecific competition on seed germination, growth and survival. The effects of salinity and plant density on the growth, reproductive output and survival of P. aviculare were investigated in the field. An additional study was performed in incubators to determine the effect of thermoperiod and salinity on seed germination. Seed germination was inhibited by increasing salinity and a thermoperiod of 35 C-day/25 C-night. High summer temperatures and increased soil salinity may explain why viable seeds remained in the soil after the spring germination period in both high- and low-salinity plots during the growth season, while soil moisture levels did not differ (P<0.05) between them. Low-salinity plots had higher plant densities and lower mortality than high-salinity plots. Survival was density-dependent in the low-salinity plots, but regulated primarily by salinity stress in the high-salinity plots. Biomass production was lower in the high-salinity than in low-salinity plots. Both intraspecific competition and salinity stress reduced growth and survival of P. aviculare.

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Homaee, M., Feddes, R.A., et al. 2002, 'A Macroscopic Water Extraction Model for Nonuniform Transient Salinity and Water Stress', Soil Science Society of America Journal, vol. 66, pp. 1764-1772.

Quantitative description of root-water uptake under combined salinity and water stress is needed to optimize crop yields and water management in arid and semiarid regions. This study was conducted to develop a simple macroscopic root-water uptake model for nonuniform transient soil water content and salinity conditions in the root zone. This new model and previous models were tested against detailed experimental data obtained with Alfalfa (Medicago sativa L.) grown in the greenhouse in packed sandy loam (Typic Haplaquent) columns. Soil water content, pressure head, and osmotic head distributions in the root zone were varied by means of the amounts, application intervals, and salinities of the irrigation water. Experimental data under separate and combined stresses were used to test the various models using mean values of soil solution osmotic and pressure heads. The simple additive reduction function provided the worst agreement with the experimental data, while for most cases the multiplicative reduction functions could not adequately account for both water and salinity stress conditions. The newly proposed linear reduction function is neither additive nor multiplicative, but was assumed that both the intersect and slope of the reduction function increased with salinity. This model provided excellent agreement with the experimental data, particularly at higher soil solution salinities. The new reduction funtion could be used with any other nonlinear salinity reduction function.

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Ingvalson, R.D., Oster, J.D., et al. 1970, 'Measurement of Water Potential and Osmotic Potential in Soil with a Combined Thermocouple Psychrometer and Salinity Sensor', Soil Science Society of America Proceedings, vol. 34, pp. 570-574.

A combined thermocouple psychrometer and salinity sensor, which is embedded in a single ceramic body, is described. This design makes possible the measurement of the water and osmotic potentials of soil water at the same location in the soil. Errors produced by spatial variations in soil solution concentration, shown to be large, were eliminated by the instrument's ability to make both measurements on a single sample of soil solution. The instrument was tested in a soil-plant-water system, and the data obtained are reported. Desaturation of the ceramic at matric potentials more negative than -2 bars was shown to have a significant effect on conductance of the salinity sensor. Correction for this effect is discussed. Measurements showed that cotton plants extracted more water from the lesssaline zones in the soil. This had the effect of lowering the water potential to approximately the same value at two depths in the soil profile at the end of a drying cycle.

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McIntyre, D.S. 1980, 'Basic Relationships for Salinity Evaluation from Measurements on Soil Solution', Australian Journal of Soil Research, vol. 18, pp. 199-206.

Relationships among total ion concentration, electrical conductivity and osmotic potential have been determined on 137 saturation extracts from Australian soils. The results are presented in graphical form with linear regression equations of best fit, and are compared with the results for western U.S.A. soils. If the relationships fitted to the U. S. data are corrected to the temperature at which the present measurements were made, the differences between the two are less than 20%. As well, the electrical conductivity, and the osmotic potential, have been estimated from the measured compositions of the extracts, and compared with the measured values. Good agreement is found for electrical conductivity over a large range, but only over a small range for osmotic potential.

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McIntyre, D.S. 1982, 'Capillary Rise from Saline Groundwater in Clay Soil Cores', Australian Journal of Soil Research, vol. 20, pp. 305-313.

The rate of salinization by capillary rise from a saline water table in wet clay soil cores, 0.60, 0.75 and 0.90 m long, and 0.25 m in diameter, is described. Tensiometer-pressure potential and electrical conductivity were measured as a function of time at vertical spacings of 0.15 m. Initially a relatively rapid rise of saline water occurred to a height of 0.30 m above the water table, but subsequent movement was very slow. Although the potential evaporation rate was only 1.0 mm/day, drying of the surface occurred quickly, and proceeded down the cores, reducing the upward moisture flux to a very low value. The salinization hazard of such a soil is low, but the possibility of application of the measurement to more permeable soils, in which salinization may be more likely, is discussed.

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McIntyre, D.S., Loveday, J., et al. 1982, 'Field Studies of Water and Salt Movement in an Irrigated Swelling Clay Soil. I: Infiltration During Ponding', Australian Journal of Soil Research, vol. 20, pp. 81-90.

Infiltration and deep percolation were measured during ponding of a saline sodic cracking clay soil, commonly used for rice production in the Riverina of New South Wales. Because gypsum may be used to ameliorate this soil for row cropping, the effect of incorporating gypsum into the plough layer was determined. Without gypsum, 292 mm water infiltrated in 379 days of ponding, wetting the profile to approximately 2.1 m. In contrast when gypsum was incorporated in the plough layer, 605 mm of water infiltrated in 145 days, and the water had penetrated beyond 4.5 m in 57 days. In the latter case, sufficient water percolated below 2.0m to raise the groundwater level by as much as 10 m. The infiltration rate for the unameliorated soil was similar to values determined by others; for the ameliorated soil, infiltration behaviour was more like that of non-sodic self-mulching grey or brown clays, and raises the questions regarding the amount of deep percolation when rice is grown on such soils.

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McIntyre, D.S., Loveday, J., et al. 1982, 'Field Studies of Water and Salt Movement in an Irrigated Swelling Clay Soil. II: Profile Hydrology During Ponding', Australian Journal of Soil Research, vol. 20, pp. 91-99.

Two plots on a saline sodic cracking clay soil, to one of which gypsum was applied at 10 t/ha, were instrumented to 4.5 m from a pit, in order to observe wetting patterns during extended inundation.

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McIntyre, D.S., Loveday, J., et al. 1982, 'Field Studies of Water and Salt Movement in an Irrigated Swelling Clay Soil. III: Salt Movement During Ponding', Australian Journal of Soil Research, vol. 20, pp. 101-105.

The effect of gypsum, incorporated into the plough layer of a saline, sodic, clay profile, on the leaching of salt, was determined from both in situ measurements, and from chloride determinations using samples taken before and after ponding. Observed differences in leaching patterns are attributed to water in the treated profile moving through interpedal macropores as well as through micropores within the peds (or matrix), but only through micropores in the untreated profile. The efficiency of the two mechanisms is discussed.

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Oster, J.D. and Ingvalson, R. 1967, 'In Situ Measurement of Soil Salinity with a Sensor', Soil Science Society of America Proceedings, vol. 31, pp. 572-574.

The electrical conductivity (EC) of the soil solution was measured in situ in a soil-plant system during three irrigation cycles. The salinity sensors used to make the measurements responded to changes in EC resulting from water uptake by the plant and salt movement in the soil profile by convection of salt in soil water. The accuracy of the measurements was estimated to be ± mmho/cm throughout the irrigation cycles.

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Richards, L.A. 1966, 'A Soil Salinity Sensor of Improved Design', Soil Science Society of America Proceedings, vol. 30, pp. 333-337.

Kemper (1959) showed that an electrical conductivity cell with spaced electrodes in fine-pored ceramic that is in contact with the film of water in soil can provide continuous measurement of the salt concentration of the soil solution. Information is given on an improved sensor of this type. The response time has been reduced to about 1 hour for bulk solutions by using a ceramic plate 1 mm thick for the sensitive element. The effect of external current paths has been eliminated by shielding and insulation, and temperature compensation has been added. Information is given on calibration procedure, along with data on the use of the sensor in irrigation tests and the relation of such data to leaching-requirement theory.

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Schaan, C.M., Devitt, D.A., et al. 2003, 'Cyclic irrigation of turfgrass using a shallow saline aquifer', Agronomy Journal, vol. 95, pp. 660-667.

A 2-yr cyclic irrigation study using shallow saline groundwater was conducted on a sports field in southern Nevada [bermudagrass (Cynodon dactylon L. 'Tifway') overseeded with perennial ryegrass (Lolium perenne L. 'Champion')]. Shallow groundwater with a salinity of 3.3 dS m^-1 was substituted for municipal water (0.9 dS m^-1) at a rate of one, two, three, or four times per seven irrigation events during the peak water demand periods of 15 May to 15 October. Salinity sensors and tensiometers were installed at depths of 10, 25, and 40 cm and recorded weekly. Midday leaf xylem water potential, canopy temperature, and turfgrass color and cover ratings were taken on a bimonthly basis. Soil salinity cycled up (as high as 24 dS m^-1) and down (baseline values of 4.0-10.0 dS m^-1) in response to substitution periods. However, the duration in which soil salinity exceeded salt tolerance threshold values for bermudagrass were short in all treatments (<21 d during the 2-yr period at the 10-cm depth). These short durations of threshold values being exceeded combined with the successful return to baseline soil salinity values during the cyclic off periods (freshwater only) led to little change in turfgrass color, cover, and plant water status. Freshwater savings as high as 50 cm yr^-1 and a reduction in as many as 62 municipal irrigation days (days irrigations took place) during the peak water demand periods occurred. Results of this experiment indicate that the cyclic irrigation strategy is feasible in the urban setting with large turfgrass areas.

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Scholl, D.G. 1978, 'A Two-element Ceramic Sensor for Matric Potential and Salinity Measurements', Soil Science Society of America Journal, vol. 42, pp. 429-432.

A two-element ceramic sensor was developed to produce optimum electricl response both to soil water matric potential and salinity. A spring-loaded housing was developed for the elements for either drill-hole or pit-face placement. The sensors were calibrated under various matric potential, salinity, and temperature conditions. An initial field test with 72 sensors was conducted under irrigated coal mine spoil conditions Laboratory and field results indicated reasonable instrument precision over a wide range of matric potential and salinity. The correlation between sensor output and water content in the field was best where the mean of several sensors was used.

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Slavich, P.G. and Petterson, G.H. 1993, 'Estimating the Electrical Conductivity of Saturated Paste Extracts from 1:5 Soil:Water Suspensions and Texture', Australian Journal of Soil Research, vol. 31, pp. 73-81.

This paper presents a method of estimating the electrical conductivity (EC) of a saturated paste extract (ECe) from the EC of a 1 to 5 soil/water suspension (EC_1:5) and an estimate of soil texture. The method has application in soil testing laboratories which routinely determine EC_1:5 but not ECe. The method of preparing the saturated paste by capillary wetting is also compared with the standard method of hand mixing.

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Todd, R.M. and Kemper, W.D. 1972, 'Soil dispersion coefficients near an evaporating surface', Soil Science Society of America Proceedings, vol. 36, no. 4, pp. 539-543.

A series of laboratory experiments was conducted to gain detailed information on water and salt movements near an evaporating surface.

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Wesseling, J. and Oster, J.D. 1973, 'Response of Salinity Sensors to Rapidly Changing Salinity', Soil Science Society of America Proceedings, vol. 37, pp. 553-557.

Based on the assumption that diffusion of solutes into and out of the sensitive element of a salinity sensor determines its response time, a theory was developed to describe the response of the sensor to changes in soil salinity. This theory was experimentally verified in solution and in soils. The response of a sensor was shown to be adequately described by a single response factor. Proper use of this factor permits the actual electrical conductivity of the soil solution to be inferred from sensor readings where soil salinity changes rapidly.

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Wood, J.D. 1978, 'Calibration Stability and Response Time for Salinity Sensors', Soil Science Society of America Journal, vol. 42, pp. 248-250.

Commercially produced salinity sensors removed from field and lysimeter experiments lasting from 3 to 5 years were tested for calibration stability relative to the original factory calibration. Significant changes in calibration occurred in up to 14% of the sensors after 4 and 5 years of use. Response to a step-change hi salinity was also examined for commercial units in a field installation. Calculated response factors were lower than those found in a previous laboratory experiment. However, response was sufficiently rapid to assure accurate readings if changes in salinity occur in time intervals exceeding 5 days.

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