Extract Electrical Conductivity Research Articles

Land Application of Treated Industrial Wastewater on a Chihuahuan Desert Shrubland: Implications for Water Quality and Mineral Deposition

Land application of wastewater conserves fresh water and recycles nutrients, but little is known of its impacts on arid and semiarid landscapes. Lagoon treated saline−sodic industrial effluent was applied from 2002–2005 to a 0.4-ha Chihuahuan Desert shrubland to assess the deposition and recovery of effluent components and changes in soil quality vis-à-vis a non-irrigated area. Effluent irrigation supplied 26% of the average annual nonstressed evapotranspiration (ET) of the native shrubs [Larrea tridentata (DC.) Coville and Prosopis glandulosa Torr. var. glandulosa], and increased both soil stress factors (sodicity, salinity, and pH) and soil fertility (N, P, and K). After 3 yr, the soil saturation extract electrical conductivity (ECe) reached as high as 6.1 dS m−1 and Cl− 76 molc m−3 at 105 cm depth under irrigated L. tridentata. After 4 yr, saturation extract sodium adsorption ratio (SARe) reached 25–35 at 7.5 cm under the irrigated shrubs and intershrub spaces. There were 27 Mg ha−1 of cumulative ionic deposits to the site comprised mostly of Na+, Cl−, and CaCO3 equivalent alkalinity, with soil analysis recovering most of the deposits (>57%) except for K+ and Na+ (8% to 13%). Subsurface leaching of and P was detected within the upper 1 m soil depth after 4 yr, and a high downward mobility of Cl− revealed the potential for deeper leaching at higher N loading rates. While long-term effects on the natural vegetation are unknown, results contribute to a limited scientific database for sustainable wastewater land application in semiarid regions.

Evaluation of 1:5 soil to water extract electrical conductivity methods

Conducting a 1:5 soil:water extract to measure electrical conductivity (EC) is an approach to assess salinity and has been the preferred method in Australia, but not commonly used in the United States where the 1:1 soil to water ratio is preferred. The objectives of this research were to 1) compare methods of agitation for determining EC1:5 and 2) to determine optimal times for equilibration for each method across a range of salinity levels determined from EC values achieved from saturated paste extracts (ECe). Soils evaluated for this study were from north central North Dakota (USA) and had ECe values ranging from 0.96 to 21.2dSm−1. For each method, nine agitation times were used, up to 48h. The three agitation methods were shaking plus centrifuging, shaking, and stirring. Agitation methods resulted in significantly different EC1:5 values for 13 out of 20 soils across the three agitation methods, and shaking plus centrifuging was significantly different (p=0.05) from stirring for all soils. In addition, 75% of the shaking plus centrifuging soils were significantly different from shaking. Based on these results, methods were analyzed separately for optimal equilibration times. The agitation times required for the three methods to reach 95 and 98% of equilibration were a function of the level of soil salinity. For soils with ECe values below 4dSm−1, over 24h was needed to obtain both 95 and 98% of equilibration for the three methods. However, less than 3 and 8h were needed to reach 95 and 98% equilibration, respectively, across methods for soils having ECe values greater than 4dSm−1. These results indicate that investigating the effect of agitation methods and times is important to help reduce variations across EC1:5 measurements.

Salinity on chalk cliffs and its influence on maritime vegetation

AbstractThe chalk cliffs of south-eastern England are liable to catastrophic cliff falls, giving edaphic conditions very variable in space and time. Chalk has ∼50% porosity, holding much water between 100 kPa and 1,000 kPa, but its availability to plants is restricted by salinity. The electrical conductivity of extracts of saturated pastes (ECs), as commonly used for agricultural soils, was used to measure the salinity of chalk and chalky soils. Studies along cliff transects between Folkestone and Dover showed that salinity thus measured was a good predictor of the distribution of both individual plant species and associations. Cliff geomorphology was far more important than distance from the sea in explaining salinity and plant distribution. We suggest that moist chalk surfaces are effectively impermeable, causing salt spray to run off during storms and concentrate in crevices, ledges and the topmost part of talus slopes, even at 400 m from the sea, which then support halophytes. We suggest that ECs coul...

IONIC DISPLACEMENT AND RECLAMATION OF SALINE‐SODIC SOILS USING CHEMICAL AMENDMENTS AND CROP ROTATION

ABSTRACTBiological, chemical and bio‐chemical strategies have been tested in the past for reclamation of saline‐sodic and sodic soils. The efficiency of two crop rotations (rice‐wheat and Sesbania‐wheat) alone or in combination with either gypsum (CaSO4.2H2O) or sulfuric acid (H2SO4) was tested for ionic displacement from four saline‐sodic soils. Pure gypsum was applied at 50 per cent of soil gypsum requirement at the time of planting rice and Sesbania, whereas 95 per cent pure sulfuric acid was added at 50 per cent soil gypsum requirement as one‐third applications by mixing with the first three irrigations. The rice crop biomass decreased at a soil saturation extract electrical conductivity (ECe) of 8 dS m−1, whereas wheat and Sesbania were influenced at a sodium adsorption ratio (SAR) of ≥40. Gypsum treatment helped the crops flourish well at these ECe and SAR levels. The infiltrated volume of water dropped with decrease in ECe : SAR ratio of soils and increase in crop biomass production. Crops rotation treatments alone helped leach sodium (Na+) and other ions successfully at SAR ≤ 21 but were less effective at SAR ≥ 40 at which point plants growth was also curtailed. Gypsum and H2SO4 treatments significantly aided leaching of Na+ and other ions with water at SAR ≥ 40 under both the crop rotations. Hence, crops effectively reclaimed soil at low sodicity level, whereas at high SAR, chemical amendments are obligatory in order to reclaim soils. This study also suggests that the required dose of H2SO4 should be applied with pre‐planting irrigation for better yield of the first crop. Copyright © 2011 John Wiley & Sons, Ltd.

Dry Bean Response to Salinity in Southern Manitoba

Expansion of dry bean (Phaseolus vulgaris L.) production into saline soil areas of Manitoba has led to increased concern regarding its yield and quality response to soil salinity. The objective of this study was to evaluate the impact of salinity on dry bean productivity in southern Manitoba, including the application of a salt tolerance model for dry bean crops. Using a coulter‐based sensor (Veris 3100, Veris Technologies, Salina, KS) to measure apparent soil electrical conductivity (ECa), surveys of dry bean fields with five levels of soil salinity conditions (very low to very high salinity zones) were created for four sites over 2 yr. High values of ECa were associated with high values of soil saturation extract electrical conductivity (ECe). Across all site years, average root‐zone salinity (ECe) values ranged from 0.77 to 11.16 dS m−1 The lowest salinity zones resulted in greater crop biomass, grain yield, harvested seed weight, and grain number, and tended to have greater plant stand densities and grain protein content than the highest salinity zones. A 50% decrease in relative crop yield was caused by ECe values between 4.88 and 8.35 dS m−1 ECa surveys were found to be an excellent tool for assessing the relative soil salinity status of study fields.

Performance of a Mobile Salinity Monitoring Device Developed for Turfgrass Situations

Spatial salinity mapping with a mobile sensor platform allowing GPS‐labeled data on turfgrass areas would facilitate site‐specific leaching programs for salinity management. A salinity monitoring device (SMD) based on 4‐Wenner array electrical resistivity (ER) electrode configuration was developed for turfgrass sites and tested on three soils at Griffin, GA and a golf course fairway in Naples, FL on two dates where the fairway received saline irrigation water. Using directed soil sampling, the SMD resulted in soil apparent soil electrical conductivity (ECa) vs. laboratory saturated paste extract electrical conductivity (ECe) linear relationships with r2 of 0.59 to 0.87 (p < 0.0002) for 0 to 10 cm and 0 to 20 cm zones at Griffin, GA. For two mapping events varying two‐ to threefold in salinity levels at the golf course fairway, the ECa vs. ECe linear regressions exhibited similar slopes, different intercepts (due to two to threefold difference in background salinity), and r2 of 0.53 to 0.58 (p < 0.002). On another fairway, a detailed spatial salinity map using geographic information systems (GIS) methods was developed using a sampling grid of 2 by 3 m, which was well within the 19 m range determined for spatial autocorrelation of the data. Our data suggest the empirical methods developed for agricultural soils for relating ECa to ECe and for determining average ECa of discrete subsurface zones may differ under turfgrass conditions due to stratification of the surface organic matter layer influencing water holding capacity, soluble salt retention, and averaging ECa within a subsurface zone.

Improvement of soil properties by application of olive oil waste

Wet olive pomace is an organic lignocellulosic material, a by-product of the olive milling process, a typical and traditional activity in many Mediterranean countries. Wet olive pomace has difficult commercialization due to its high moisture content of 55–65%, that causes a noticeable increase in oil extraction costs. However, it could be conveniently reused in agriculture as a valid soil amendment to improve soil fertility and structure. Here, we studied the effects of the application of increasing amounts of non-fermented wet pomace on the fertility of a silty-clay soil, grown with 3 crops in succession: sunflower-wheat-wheat. The experiments were conducted at the Agricultural Faculty of Bari, Italy, on a Pachic Hoploxeroll soil characterized by illite and kaolinite and large amounts of Fe and Al sesquioxides. We compared the effect of wet pomace applied at amounts ranging from 0 to 210 Mg ha−1, incorporated 60 days prior to sunflower sowing. In the wheat late season of the second year, average samples from the 0–0.60 m layer were taken and tested for structural stability, organic matter, total nitrogen, available phosphorus, exchangeable potassium, pH and saturation extract electrical conductivity. The results indicate that the application of wet pomace induces a general improvement in soil fertility. In particular, the incorporation of increasing amounts of wet pomace improved nutrient content. For instance, an application of 210 Mg ha−1 of wet pomace increased soil organic matter by +84%, total N by +0.90 g kg−1, available P by +79.40 mg kg−1 and exchangeable K by +80 mg kg−1. We also observed an improvement in soil structure, which is of particular importance in hot, arid environments and in sustainable agricultural systems.

Soil solution and exchange complex response to repeated wetting–drying with modestly saline–sodic water

Coal bed natural gas (CBNG) extraction in the Powder River (PR) Basin of Wyoming and Montana produces modestly saline-sodic wastewater, which may have electrical conductivity (EC) and sodium adsorption ratios (SAR) exceeding accepted thresholds for irrigation (EC = 3 dS m−1, SAR = 12 (mmolc l−1)1/2. As an approach to managing large volumes of CBNG-produced water, treatment processes have been developed to adjust produced water salinity and sodicity to published irrigation guidelines and legislated in-stream standards. The objective of this laboratory study was to assess acute and chronic soil solution EC and SAR responses to various wetting regimes simulating repeated flood irrigation with treated CBNG product water, followed by single rainfall events. Fifty-four soil samples from irrigated fields in southeast Montana were subjected to simulated PR water or CBNG water treated to EC and SAR values accepted as thresholds for designation of saline × sodic water, in a single wetting event, five wetting–drying events, or five wetting–drying events, followed by leaching with distilled water. Resultant saturated paste extract EC (ECe) and SAR of soils having 33% clay. Repeated wetting with PR water having EC of 1.56 dS m−1 and SAR of 4.54 led to SAR 3 dS m−1 and SAR near 12. Subsequent inundation and drainage with distilled water, simulating rainfall-quality leaching, reduced ECe and SAR more often in coarse-textured, high salt content soils than in finer-textured, lower salt content soils. Decreases in ECe upon leaching with distilled water were of greater magnitude than corresponding decreases in SAR, reinforcing supposition of sodium-induced dispersion of fine-textured soils as a consequence of rainfall following irrigation with water having salinity and sodicity levels equal to previously published thresholds.

Phytotoxicity of Biosolids Compost at Different Degrees of Maturity Compared to Biosolids and Animal Manures

Biosolids compost is a good organic amendment but immature compost can exhibit phytotoxic behavior which can be attributed to different toxic substances. Our objective was to determine the phytotoxicity of: i) Biosolids; ii) Mix of biosolids and wood sawdust sampled a day after composting started; iii) The same material sampled at the end of the thermophilic stage; iv) cured compost; v) cow manure and vi) horse manure A germination bioassay was carried out using Lolium perenne (ryegrass) seeds: germination and root growth percentage were determined as well as electrical conductivity, pH, phenol content and volatile organic acids. In three treatments, Ni, Pb, Zn, Cu and Cd were also determined. Ammonia volatilization was determined during biosolids composting. The germination percentage varied from 67% to 95% but the inhibition of root growth appears to be a more sensitive phytotoxicity indicator (18% to 74%. Phytotoxic effects on germinating ryegrass were mainly related to extract pH and electrical conductivity. Potentially toxic elements, volatile organic acids, phenolic compounds and ammonia were not related to germination.

Variability in the Physical and Chemical Properties of Retail Potting Media

Popular press articles report that consumers often experience inconsistent results with retail potting media; however, few reports in the popular or scientific literature have quantified the variability in media properties. The purpose of this study was to assess the variability in physical and chemical properties among different brands of retail potting media and within certain brands. Twenty-four different packages of branded media, and multiple packages of five brands, were acquired from nine regional and national retail chain stores located in the Salt Lake City, Utah, area. Samples were analyzed for five physical and nine chemical properties. The coefficients of variation (cvs) among brands for initial gravimetric water content, bulk density, porosity, water retention, and air space were 85%, 74%, 21%, 59%, and 44%, respectively. The cvs among brands for saturated media (SM) pH, SM extract electrical conductivity (EC), nitrate-nitrogen (NO3-N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), total carbon (C), total nitrogen (N), and C:N ratio were 18%, 81%, 132%, 153%, 96%, 78%, 71%, 36%, 45%, and 49%, respectively. Only one of the 24 brands met all published standards for chemical properties of premium media. Thirteen of the brands did not meet standards for NO3-N; 12 did not meet standards for pH; and six did not meet standards for EC. There was more variation in physical and chemical properties among brands than within a brand of media. Label information describing media composition was not consistent with certain physical and chemical properties. No recommendations can be made which would allow consumers to select media that meets published standards. These results indicate better awareness of and/or adherence to standards is needed by the retail media industry to improve product quality and consistency.

A survey of the cation content of piggery effluents and some consequences of their use to irrigate soils

Piggery effluent contains high concentrations of potassium, and its repeated irrigation raises soil exchangeable potassium to levels, relative to divalent cations, that may degrade soil structure. We surveyed 6 big piggeries extending from south-eastern Queensland on a self-mulching Vertosol, to an Arenic Rudosol in south-eastern South Australia. We sampled effluent used for irrigation and also soil profiles to permit 'fenceline' comparisons between soils that had and had not been irrigated. The major water-soluble cations sodium (Na+), potassium (K+), calcium (Ca2+), and magnesium (Mg2+) were measured in the effluent and the soil saturation extracts, and also their exchangeable forms on air-dried soil samples. Ammonium-nitrogen (NH4+-N) was also assayed. The effluents were similar, with pH values between 7.5 and 8 together with very high water-soluble NH4-N, lower values for K+ and Na+, and quite low concentrations of Ca2+ and Mg2+. Cation concentrations varied across effluents; sodium and potassium adsorption ratios (SAR and KAR) were relatively constant but smaller than an ammonium adsorption ratio (Am-AR), which we conceive to estimate the influence of NH4+-N relative to the divalent cations in the effluent. Exchangeable K+ ratios in all profiles that had been irrigated were greater than their non-irrigated partners, as were the KAR values in their saturation extracts. Despite high concentrations of NH4+-N and high values of Am-AR in the effluents, there was no evidence of exchangeable NH4+ in the soils when sampled, which, we presume, is rapidly taken up by plants or oxidised. We present data that support a useful relationship between total cation content and effluent and the soil saturation extract electrical conductivity (EC), We also observed a modest increase in the EC of the saturation extract of irrigated soils. Farm records were insufficient to permit material balance calculations.

Changes in antioxidant activity in sub-cellular fractions of tolerant and susceptible wheat genotypes in response to long term salt stress

Effects of long term, medium level (electrical conductivity of extract (ECe)=6.85 dS m −1) sodium chloride (NaCl) salinity were studied in tolerant (Kharchia 65) and susceptible (HD 2687) wheat genotypes. NaCl salinity caused decrease in relative water content (RWC), chlorophyll (CHL), membrane stability index (MSI) and ascorbic acid (AA) content, and increased the contents of hydrogen peroxide (H 2O 2), thiobarbituric acid reactive substances (TBARS) (measure of lipid peroxidation) and activities of superoxide dismutase (SOD), its various isozymes, ascorbate peroxidase (APOX) and glutathione reductase (GR) in wheat genotypes Kharchia 65 (tolerant) and HD 2687 (susceptible). Salinity tolerant wheat cv. Kharchia 65 showed less decline in RWC, CHL, MSI estimated in whole tissue than salt sensitive HD 2687. Kharchia 65 also exhibited less decrease in AA content, less increase in H 2O 2, TBARS contents and higher increase in SOD and its isozymes, APOX and GR in all sub-cellular fractions than salt sensitive HD 2687. H 2O 2, TBARS contents and AA contents were higher in chloroplastic fraction. Chloroplastic fraction showed higher total SOD, APOX and GR activity, followed by mitochondrial fraction in case of total SOD and GR, while cytosolic fraction was in second place in case of APOX activity. Though Mn–SOD activity was highest in mitochondrial fraction, but residual activity was also observed in cytosolic fraction. Cu/Zn–SOD and Fe–SOD were observed in all the sub-cellular fractions, however, the activities were higher in chloroplastic fraction for both the isoforms. Total Cu/Zn–SOD activity, sum of activity observed in all the fractions, was higher than other SOD isoforms. Susceptibility of HD 2687 to long-term salinity stress seems to be due to relatively less induction of SOD isozymes, no induction in chloroplastic and mitochondrial APOX and cytosolic GR and decrease in chloroplastic GR under salt stress resulting in higher oxidative stress in the form of H 2O 2 and TBARS contents and decrease in MSI and CHL.

Water use and salt accumulation by Eucalyptus camaldulensis and Casuarina cunninghamiana on a site with shallow saline groundwater

Tree growth, water use, climate, soil salinity and groundwater conditions were monitored over a 3-year period in an unirrigated 5–8-year-old plantation in northern Victoria, within an area where groundwater pumping is in use for control of shallow watertables and salinisation of irrigated farmland. Diameter and sapwood area of Casuarina cunninghamiana increased twice as rapidly as Eucalyptus camaldulensis, in plots with initially equal mean diameter. C. cunninghamiana had greater sapwood area but lower sap flux density, so that the daily and annual water use did not differ significantly between species. Average single tree water use determined by the heat pulse method varied from less than 10 l day −1 in winter to over 30 l day −1 in summer. Stand water use averaged 0.9–1.0 mm day −1 over 2 years, and was evidently limited by soil water availability. The leaf area index (LAI) of the E. camaldulensis stand was estimated as 2.07 and the mean ratio of leaf area to sapwood area as 3815 m 2 m −2. This ratio increased with sapwood area in small trees. Hydraulic properties of the soil profile were inferred from measurements of moisture content and matric potential at 30 cm depth intervals to 390 cm, indicating the presence of a medium clay layer with heavy clay above and below. Salinity and chloride distribution were also determined, indicating slight-to-moderate salinity below 30 cm depth reaching a maximum (saturation extract electrical conductivity 8 dS m −1) at around 200 cm. Saturated hydraulic conductivity of the heavy clay was estimated as 3 mm day −1. Daily watertable depth observations were used to parameterise a water balance model to predict the uptake of water from unsaturated soil and shallow groundwater based on measured daily water use and rainfall, and accounting for the influence of groundwater pumping. Modelled results indicated that more than half the tree water uptake (170–220 mm year −1) was drawn from the groundwater. Both recharge and discharge of the groundwater occurred annually, but discharge was predominant. Intensive monitoring of soil salinity at 100–400 cm depth using buried sensors demonstrated substantial seasonal variation, apparently related to watertable movements. The average soil solution salinity rose by over 5 dS m −1 in 32 months of monitoring, estimated to correspond to chloride accumulation of more than 4 kg m −2. These values cannot be reconciled with the observed water use and salinity below the maximum watertable depth, and may indicate lateral inflow of more saline perched groundwater within the medium clay layer. The results are expected to contribute toward the development and validation of models for predicting the sustainability and environmental benefit of tree plantations in areas with shallow saline groundwater.

Sulfate uptake by salinity‐tolerant plant species

Abstract High soluble‐sulfate (SO4) concentrations affect water quality, soil chemistry, plant sulfur (S) levels, and possibly ruminant‐animal health. The objective of this greenhouse pot study was to determine the potential for accumulating high levels of S by tansy mustard (Descurainia pinnata (Walt.) Britton), kochia (Kochia scoparia L. Schrad.), yellow sweet clover (Melilotus officinalis L.), slender wheatgrass (Elymus trachycaulus (Link) Gould ex Shinners), and sunflower (Helianthus annuus L.). Plants were grown on both a Brinegar (fine‐loamy Ultic Argixeroll) and Portneuf (coarse silty Durixerollic Calciorthid) soil. Each species received five‐SO4 levels. The saturation extract electrical conductivity (EC) of the cropped soils ranged from 6 to 16 dS/m, while the soluble SO4 varied from 16 to 200 mmolc/kg soil. Soil solutions were saturated or very nearly saturated with respect to gypsum at the conclusion of each study. Plant dry matter yield, except of grass growing on the non‐calcareous soil, was not reduced by SO4 treatment nor by the sulfate‐induced decrease in mole fraction of calcium (Ca)/(sum cations) to values less than 0.10 for kochia and grass. Sulfur concentration in the plants ranged from 2.5 mg/g in grass to 10 mg/g in mustard and for each species was linearly related to the SO4 treatment and soil‐SO4 activity. Plant SO4‐S values ranged from 70 μg/g in the grass to nearly 900 μg/g in mustard. Total nitrogen (N): organic S was 4.4, 7.5, 11.4, 16.5, and 5.8 for mustard, kochia, clover, grass, and sunflower, respectively. It was concluded that these species could accumulate high levels of S in the above ground tissue.

Corn Yield and Salinity Response to Irrigation on Slowly Permeable Subsoils

AbstractCrop yields in the northern Great Plains often could be improved with irrigation but many soils of this region have been considered nonirrigable because of their low hydraulic conductivity. This project was initiated to determine the leaching characteristics when irrigating two of these soils and to determine if harmful salinity increases would result from irrigation. We measured corn (Zea mays L.) yield and soil saturation extract electrical conductivity (ECe) and sodium adsorption ratio (SARe) in response to irrigation plus precipitation of one, two, and three times the calculated evapotranspiration and to N fertility of 100 and 200 kg N/ha. The study was conducted for 5 yr at one site and 6 yr at another site, both in the northern Great Plains. Yield and increase of ECe at 100 kg N/ha were less than at 200 kg N/ha. At both sites, ECe increased but corn yield did not decrease during this experiment. The SARe increased for all treatments but the maximum observed was <10. Excess irrigation usually had no effect on yield and did not decrease yield. Such excess irrigation provided salinity control by leaching. Precipitation also leached these soils. Our data indicate that the soils tested, the top 2.3 m of the soil profiles at two sites, allow enough leaching to permit effective well‐managed irrigation.

Sodium Adsorption Ratio Screening Procedure for Soils Using pH and Electrical Conductivity

AbstractSoils with sodium adsorption ratios (SAR) <10 are generally considered to be below the threshold for potential Na hazard. The impetus for developing this screening procedure was to reduce the resources dedicated to determining precise SAR values in situations when simply knowing that the SAR is below the designated threshold is sufficient. The model was developed using 1000 samples and validated on a 24 000‐sample data set from two different laboratories operating in the western USA. The screening procedure uses empirically derived combinations of saturated soil paste pH (pHs) and extract electrical conductivity (ECe) to predict if the SAR is above or below 10, or whether Ca + Mg and Na must be analyzed to determine the SAR. For some combinations of pHs and ECe, the ratio of Ca + Mg to estimated total cations [ETC = ECe(10)] is used to decide whether Na must be analyzed. On average, the model incorrectly predicted that the SAR was <10 when the actual value was > 10 in only six out of 1000 samples. In addition, about 20% of the samples required Ca + Mg and Na analyses when the SAR was < 10. For the data sets tested, the screening procedure could have reduced the number of Ca + Mg and Na analyses by 50% with little loss of information about the potential Na hazard of the soils.

Application of Härtel's turbidity test across Europe

The history and development of Härtel's turbidity test ("Trübungstest") for investigating the effects of sulphur dioxide on conifer needles are briefly reviewed. The turbidity test was applied to samples of Norway spruce (Piceaabies (L.) Karst.) and Scots pine (Pinussylvestris L.) needles from 13 sites in western Europe, from southwestern Germany to northeastern Scotland. Turbidity and electrical conductivity of the needle extracts were measured on duplicate samples of current-year, 1-year-old, and 2-year-old needles. The greatest differences among sites were observed for 2-year-old needles, but these differences were not related to needle sulphur content, nor to exposure to sulphur dioxide. The largest values were from British sites, and the smallest were from Dutch sites, with German sites intermediate. Turbidity values for both tree species were positively correlated (p < 0.01) with electrical conductivity of extracts, amounts of leaf surface dust, and total foliar calcium and magnesium; they were negatively correlated with amounts of chloroform-extractable wax and the acidity of macerated needles. Turbidity values for 2-year-old Norway spruce needles and conductivity values for 2-year old Scots pine needles were significantly greater (p < 0.05) within sites for trees with visible decline symptoms (needle loss and discoloration). The large differences in turbidity values among sites suggest that the turbidity test provides a simple method for characterizing conifer needles, and that a better understanding of the basis of the test may lead to a better understanding of the physiological and biochemical status of conifer foliage.

The role of soil spatial variability investigation in the management of the Chad Basin vertisols of N.E. Nigeria

The Chad Basin of North-Eastern Nigeria is endowed with a vast expanse of vertisols that are not only rich in plant nutrient elements but also have a high water-holding capacity. These soils therefore are capable of supporting a large-scale production of food and forage crops alike. The ability of the soils to support large scale cultivation of forage crops is particularly significant in view of the fact that the North-East is the leading producer of livestock in Nigeria. Prediction of soil behaviour and crop productivity are conventionally based on soil test results. The reliability of soil test results on which management decisions are based cannot be greater than the reliability of the soil samples from which the results are obtained. The samples collected from the field must therefore be representative of that field. A procedure for obtaining representative soil samples, based on an adequate assessment of the soil spatial variability, is therefore presented. Surface soil samples (0–15 cm) were collected from 100 locations spaced at regular intervals of 2 m within a transect sited in the middle of a 2 ha field in the Chad Basin of North-Eastern Nigeria. The samples were analysed for exchangeable cations, saturation extract electrical conductivity (EC e ), particle size distribution, bulk density, organic carbon and pH. All the soil properties investigated were found to be normally distributed. Estimated sample autocorrelograms suggested that the observations of Exchangeable Na + , Exchangeable sodium percentage (ESP), EC e , Bulk density and silt content were spatially independent. Exchangeable Potassium and Magnesium, pH, percent sand and percent clay exhibited fairly strong spatial dependence while exchangeable calcium and organic carbon exhibited weak spatial dependence. The implications of the spatial dependence or independence of these soil properties in selecting appropriate soil sampling plans are discussed. Sample size calculations revealed that while it requires only one sample to estimate the mean values of clay content and pH within ±10% of the population means of these properties at the 95% confidence level, 696 samples would be required to estimate the mean value of exchangeable magnesium for the study area at the same precision level. The implications of these estimates of sample number requirements in obtaining reliable soil test results for improved management and enhanced productivity of these vertisols are discussed.

SOIL SALINITY STATUS AND ITS RELATION TO SOME OF THE SOIL AND LAND PROPERTIES OF THREE IRRIGATION DISTRICTS IN SOUTHERN ALBERTA

A detailed soil salinity survey was carried out in three of the 13 irrigation districts in southern Alberta. About 30 quarter-sections in each district were randomly selected for soil sampling. The location, distance from water supply ditches, slope of the land, and depth to till and water table at each site were recorded. Soil texture and electrical conductivity of extracts of soil samples were determined in the laboratory. The extent of the area with a soil salinity level of 4 dS/m or more is 5% of the total surveyed land in the Western Block of the St. Mary River Irrigation District (WSMRID), 6% in the Lethbridge Northern Irrigation District (LNID) and 9% in the Taber Irrigation District (TID). These values are not as high as others have previously estimated. The salinity level of the soil at each site was found to vary with its location and distance from water supply ditches in the WSMRID and LNID, clay content in the 0- to 120-cm depth in the WSMRID and TID, and water table level in the TID. Key words: Soil texture, EC, SAR, pH

Predicting Bulk Soil Electrical Conductivity versus Saturation Paste Extract Electrical Conductivity Calibrations from Soil Properties1

Predicting Bulk Soil Electrical Conductivity versus Saturation Paste Extract Electrical Conductivity Calibrations from Soil Properties1