Conductivity Of Saturated Paste Extract Research Articles

Ameliorating saline‐sodic soils: A global meta‐analysis of field studies on the influence of exogenous amendments on crop yield

AbstractAs the demand for food continues to rise, soil salinization and sodification pose an increasingly pressing challenge. Currently, there is a knowledge gap regarding how to effectively improve saline‐sodic soils to support sustainable agricultural production, especially the lack of systematic analysis on the effects of different amendments at a global scale. To address this gap, this study aims to explore the feasibility of using exogenous amendments to ameliorate saline‐sodic soils, conducting a global‐scale meta‐analysis based on 685 data pairs from 70 published studies. Our results showed that applying amendments to saline‐sodic soils significantly reduced electrical conductivity of saturated paste extract (ECe) by 33.0% and exchangeable sodium percentage (ESP) by 44.6%, while simultaneously increasing crop yield by 50.7%. Heterogeneity analysis further unveiled significant variations (p < 0.05) in the overall effect size, driven by factors such as initial soil properties (salinity and ESP levels), amendment type, climate and practical management conditions (application dose and experimental duration). The categorical variable analysis showed that, compared to soils with other salinization levels, the application of amendments in severe salinization soils was most effective in reducing soil ECe and enhancing crop yield. Considering the goals of mitigating soil salinity, sodicity, and increasing crop yield, the study suggests the application of mixed‐type amendments in practical settings. It is noteworthy that while extremely high doses (greater than 40 t ha−1) effectively increased crop yield, they also posed a risk of salt accumulation. In conclusion, this research offers critical insights for sustainable agriculture, guiding future work on soil health and food security in the context of global environmental challenges.

Comparative Evaluation of Methods for Estimation of Soil Salinity

Different methods to estimate electrical conductivity (EC) of saturated soil paste extract (ECe) of 1:2 and 1:5 soil: water suspensions were evaluated. Soil samples were taken from different depths (viz. 0-15, 15-30, 30-45, 45-60, and 60-90 cm) of the wheat field under irrigated saline regimes ranging from 1.5 to 12 dSm-1. The relationship between the electrical conductivity of saturated paste extract (ECe) and soil-water suspension extracts (i.e., EC1:2 and EC1:5) was established beside the development of regression models and conversion factors. Regression models relating ECe with EC1:2, EC1:5 were developed with coefficients of determination (R2) 0.98 and 0.99 respectively. The average conversion factor between ECe~ EC1:2 and ECe~ EC1:5 were 2.7 and 7.7, respectively. Methods standardized in the study can be used to estimate the EC of different saturated soil paste extract ratios, which will be less cumbersome and significantly reduce the estimation time.

A Trade-Off between the Growing Performance and Sowing Density of Sunflower (Helianthus annuus L.) under Fertigation in an Arid Saline Area

Sunflower is one of the pioneer crops cultivated in salt-affected arid areas. The influences of sowing density on the growth performance of this crop under fertigation conditions have not been well studied. This study arranged four sowing density treatments, 41,667, 35,714, 31,250, and 27,778 plants ha−1, marked as D30, D35, D40, and D45, respectively, to reveal the relationships between soil salinity, growth performance, and sowing density under drip fertigation conditions. The results showed that the electrical conductivity of saturated paste extracts (ECe) decreased during the growing seasons but increased on the topsoil during the non-growing seasons in all of the treatments. The sowing densities had remarkable influences on the ECe in the 0–40 cm soil layer (ECe-40). The average ECe-40 during the two seasons for treatments D30–D45 correspondingly decreased by 7.0%, 33.9%, 11.1%, and 15.8% when compared to the original value. The soil pH in the 0–40 cm soil layer during the two seasons for treatments D30–D45 correspondingly decreased by −0.03, 0.20, 0.20, and 0.27 when compared to the original value. Increasing the spacing in the rows could promote the stem diameter, plant biomass, and proportion of biomass allocated underground. The yield and related yield components in this experiment under fertigation were significantly higher than those under surface irrigation. A sowing density between 31,250 and 35,714 plants ha−1 could ensure both the high yield and high morphological quality of the seeds, which could be recommended for sunflower cultivation under drip fertigation conditions.

Evaluation analysis of the saturated paste method for determining typical coastal saline soil salinity

The electrical conductivity of saturated paste extracts (ECe) is more widely used as the laboratory method for estimating soil salinity compared to the soil-water ratio method. However, the current saturated paste process is time consuming and mainly based on subjective experience, and the quantitative relationships among the factors influencing the saturated paste process are not clear. In order to understand and optimize the process of soil salinity determination by saturated paste method, an experiment involving the process of making saturated paste and the key factors in salt determination was carried out on coastal saline silt and sandy loam soils: amount of water added, soaking time, number of centrifugations, and soil particle size. These test factors had clear impact on soil salinity results (both ECe and mass salt content) and pH. Based on the principle of obtaining more mass salt content in this study, suitable parameters for the production of saturated slurries were proposed as follows: (1) the amount of distilled water added to the soil sample should be 2.2 times the saturated water content of the soil; (2) the equilibration time of saturated paste was reduced from 18 to 12 h; (3) only 40 % of the full salt content was obtained by one centrifugation and obtaining 80 % requires three centrifugations; and (4) 0.25–0.50 and 1–2 mm of particle-size sieving should be used to prepare samples of silt and sandy loam soils, respectively.

Plastic film buried in a low-lying strongly salt-affected wasteland: An effective desalinization approach should not be ignored for Amorpha fruticosa afforestation

Cutting off the upward movement of salts by capillary barriers may be an effective approach to control the root-zone salt accumulation in a low-lying salt-affected wasteland with high evaporation. This study aimed to determine whether buried plastic film (BPF), as an ignored desalinization approach, could better sustainably ameliorate salt-affected soil environment especially soil salinity than common capillary barriers (buried maize straw, BMS; buried sand, BS) and CK (a control without buried material) during Amorpha fruticosa afforestation. All the capillary barriers especially BPF effectively reduced electrical conductivity of saturated paste extracts (ECe) compared to CK in both years mainly due to its greater effectiveness of salts isolation, and gravitational washing increasingly via more preferential pathways indicated by its higher fine-root mass density (FRMD). Capillary barriers varyingly improved the fertility and structure in different soil layers. BPF reduced soil organic carbon (SOC) in 0–20 cm most in 2016, but increased it most in 2017; while BMS increased SOC in 20–40 cm most in both years. In both years, available nitrogen (AN) in 0–20 cm increased most for BPF, while AN in 20–40 cm did for BMS. Similarly, BPF improved better in soil structure (mean weight diameter, MWD; soil total porosity, STP) in 0–20 cm while BMS did in 20–40 cm. As the salinity declined, BPF was more beneficial to the stand establishment and plant growth which in turn further bio-physicochemically improved salt-affected soil environment. BPF was not only far less costly than BMS or BS, but also obviously produced more yield and thus greater net revenue in the second year. Thus, BPF is a promising alternative for desalinization during the afforestation of salt-tolerant plants in the similar strongly salt-affected areas.

Morphophysiological responses of table beet irrigated with saline water under application of humic substances

The use of saline water is an alternative for irrigating agricultural crops, especially in the Brazilian Northeastern semi-arid region, where water quality is limited in most cases. Thus, the objective was to evaluate the morphophysiological responses of table beet cv. “Wonder” irrigated with saline waters under the application of humic substances. The experiment was conducted under a randomized block design, with six replications in a 6 x 4 x 5 factorial scheme, referring to six electrical conductivities of irrigation water (ECw): 0.5; 1.5; 2.5; 3.5; 4.5 and 5.5 dS m-¹, four humic substances rates (HS) (0; 10; 20 and 30 ml per plant), and five stages of assessment (23, 38, 53, 68 and 83 days after emergency). The characteristics evaluated were: plant height, number of leaves, leaf area, chlorophyll content (a, b and total), stomatal conductance, transpiration, net photosynthesis and CO2 internal concentration, and in the soil, the soil pH and the electrical conductivity of saturated paste extract. The increase of salinity reduced growth, chlorophyll a content, and the stomatal conductance of beet plants. The application rate of 30 ml per plant of humic substances promotes an increase in stomatal conductance. The application of humic substances raises the pH in sandy acidic soils. It is recommended to irrigate table beet plants with water of 0.5 dS m-1 associated with the application of 30 mL per plant of humic substances

Drip‐irrigation using highly saline groundwater increases sunflower yield in heavily saline soil

AbstractTo improve global food security, techniques for sustainability managing salinity are needed. The objective of this study was to find a sustainable cultivating method for grain production using saline groundwater. A field experiment was conducted to determine the effect of drip irrigation with saline water (EC = 9.5 dS m–1) (DIS), drip irrigation with freshwater (electrical conductivity [EC] = 1.3 dS m–1) (DIF), and flood irrigation with freshwater (CK) on sunflower (Helianthus annuus L.) yields. The cultivation pattern of “scheduled drip irrigation + mulched ridge” was adopted in DIS and DIF, while that in CK was the local pattern of “flood irrigation + flat mulch”. Results showed that drip irrigation with saline water and drip irrigation with freshwater saved 95% and 43 freshwater when compared with CK. After 2 yr, soil electrical conductivity of saturated paste extracts (ECe) in the surface 40 cm decreased from 22.9 to 6.4 dS m–1 in DIS and from 17.9 to 5.4 in DIF. The calculated desalinization rates were 72.1% for DIS and 69.3% for DIF. The sunflower yield in DIS and DIF increased by 12.1 and 37.0% and the economic benefit correspondingly increased by 29.6 and 52.5% when compared with CK after 2 yr. The drip irrigation with saline groundwater had remarkable advantages in saving freshwater, leaching salt, and increasing income.

Soil environment and growth adaptation strategies of Amorpha fruticosa as affected by mulching in a moderately saline wasteland

AbstractUnderstanding the growth adaptive strategies of Amorpha fruticosa in response to the changes of saline soil environment under different mulch types (plastic mulch [PM]; sand mulch [SM]; rice straw mulch [RSM]; and control with non‐mulching [CK]) is very important, as this determines afforestation success in a moderately saline soil. The species' soil microenvironments, fine root traits, and biomass allocation patterns were investigated in 2016 and 2017. Compared to CK, electrical conductivity of saturated paste extracts (ECe) reduced significantly under the mulching treatments especially under PM. Both PM and SM effectively increased soil temperature (Tsoil) and available nitrogen (AN), but reduced soil organic carbon (SOC) in 2016; while RSM increased soil nutrients, but reduced Tsoil. The A. fruticosa under RSM (following PM and SM) invested more biomass, to shoots relative to roots, to coarse roots relative to fine roots, and to stems and leaves at the expense of coarse roots and fine roots from 2016 to 2017, as its saline soil environment especially the low Tsoil improved. In both years, the fine roots of A. fruticosa under PM employed exploitation potential or ‘extensive strategy’ (fine root mass density; fine root length density) more successfully at the 0–40 cm, while the fine roots under CK used higher exploitation efficiency or ‘intensive strategy’ (specific root length; and specific root area). The indicators of intensive strategy at the 40–60 cm were higher under PM than SM and RSM. Therefore, PM will better help A. fruticosa adapt to the harsh soil environment during afforestation in a moderately saline wasteland.

Mulches Improve Ridge‐tillage Tomato Production under Drip Irrigation with Saline Water

Core Ideas Soil salinity three years after first growing season was fluctuated slightly.Soil salinity under wheat straw was lower than both waterproof and pervious plastic mulch.Wheat straw improved tomato yield, followed by black waterproof plastic mulch. Fresh water resources in the North China Plain are declining due to increasing industrial and domestic water use. These uses raise the agricultural demand for low quality water. To provide appropriate management techniques for safely using saline water, different mulching materials were tested on ridge‐tillage tomato (Lycopersicon esculentum Mill.). Four treatments: control (bare land, CK), black plastic (BPM), black sheet net (BSN), and wheat straw (SM) were designed to: (i) evaluate the effects of mulching on the irrigation amount, soil salinity, tomato yield, and irrigation water productivity (IWP); and (ii) develop integrated irrigation strategies using saline water securely. The average required water for the SM and BPM treatments reduced by 12 and 20%, respectively. Electrical conductivity of saturated paste extracts (ECe) increased from 1.91 to 4.07 dS m−1 in 0‐ to 40‐cm root zone and from 2.33 to 4.24 dS m−1 in 0‐ to 120‐cm soil profile after the first year irrigation, and then fluctuated slightly during the next 3 yr due to precipitation and evaporation. The ECe for the SM treatment was always the least in 4 yr. Compared with CK, the BPM and SM treatments over 4 yr increased the average tomato yield by 26 and 42%, and increased the average IWP by 62 and 70%, respectively. Therefore, straw mulching was the best mulching material to safely use saline water of <6.3 dS m−1 for the ridge‐tillage tomato under drip irrigation, followed by black plastic mulching, in a temperate semi humid monsoon climate zone.

Salt leaching of heavy coastal saline silty soil by controlling the soil matric potential

Techniques of drip irrigation are broadly applied for the reclamation of saline-alkali lands, during which effective management of water use to accelerate salt leaching is essential for crop production. In 2017, a field experiment with five treatments of soil matric potential (SMP) levels of −5, −10, −15, −20, and −25 kPa was conducted in heavy saline silty soil land in Bohai Bay, China to study the effects of drip irrigation on salt leaching. The results showed that salt leaching was enhanced with increasing SMP, particularly under an SMP of −5 kPa within a 30 cm soil profile depth and 15 cm distance from the dripper, and the average electrical conductivity of saturated paste extracts (ECe) decreased from 13.8 to 1.52 dS/m. Water consumption increased with increasing SMP, but the yield of oil sunflower did not differ significantly between SMPs of –5 and –10 kPa. These findings indicated that a relatively high crop yield of oil sunflower and effective salt leaching can be achieved if the SMP can be controlled at –10 kPa in heavy saline silty soil.

Empirical model and variability of soil salinity in the coastal zone of Bangladesh

Soil salinity expressed by electrical conductivity is a threat to crop production. The study aims were to establish relationships of electrical conductivity with its relevant soil properties, and analyze variability of soil salinity in the coastal zone of Bangladesh. A total of 150 geo-referenced saline soil samples from three coastal districts (Khulna, Satkhira and Bhola) of Bangladesh were analyzed for electrical conductivity of saturated paste extract (ECe), salt cations and other soil properties related to salinity. Statistical and geostatistical analyses were done as required. Moderate to strong significant regression relationships (R 2 =0.42 to 0.94) were found between ECe and salt cations (ECe=43.12*Na 2 -46.36*Na+13.97; ECe=12.26*K-2.5;ECe=1.16*Ca-1.97; ECe=0.32*Mg 2 -1.60*Mg+3.53) of the soils. On the contrary, weak relationships (R 2 =0.05 to 0.21) were found between ECe and other soil properties (ECe=4.41*organic carbon-0.56; ECe=-1.71*Txw (soil texture)+3.98;ECe=0.35*cation exchange capacity-1.98; ECe=0.06*specific surface area-0.55). Khulna soils (CV=65.99%) showed lower statistical variations while Satkhira (CV=97%) and Bhola (CV=105%) soils showed higher statistical variations for ECe. In contrast, Khulna, Satkhira and Bhola soils showed strong, moderate and weak spatial dependency for ECe, respectively. Interpolated spatial distribution maps of ECe showed variations in individual districts of study areas. The findings would assist soil scientists or farm managers to understand and/or manage saline soils, specially the soils of coastal zone of Bangladesh.

Saline–Sodic Soils: Potential Sources of Nitrous Oxide and Carbon Dioxide Emissions?

Increasing salt–affected agricultural land due to low precipitation, high surface evaporation, irrigation with saline water, and poor cultural practices has triggered the interest to understand the influence of salt on nitrous oxide (N2O) and carbon dioxide (CO2) emissions from soil. Three soils with varying electrical conductivity of saturated paste extract (ECe) (0.44–7.20 dS m−1) and sodium adsorption ratio of saturated paste extract (SARe) (1.0–27.7), two saline–sodic soils (S2 and S3) and a non–saline, non–sodic soil (S1), were incubated at moisture levels of 40%, 60%, and 80% water–filled pore space (WFPS) for 30 d, with or without nitrogen (N) fertilizer addition (urea at 525 µg g−1 soil). Evolving CO2 and N2O were estimated by analyzing the collected gas samples during the incubation period. Across all moisture and N levels, the cumulative N2O emissions increased significantly by 39.8% and 42.4% in S2 and S3, respectively, compared to S1. The cumulative CO2 emission from the three soils did not differ significantly as a result of the complex interactions of salinity and sodicity. Moisture had no significant effect on N2O emissions, but cumulative CO2 emissions increased significantly with an increase in moisture. Addition of N significantly increased cumulative N2O and CO2 emissions. These showed that saline–sodic soils can be a significant contributor of N2O to the environment compared to non–saline, non–sodic soils. The application of N fertilizer, irrigation, and precipitation may potentially increase greenhouse gas (N2O and CO2) releases from saline–sodic soils.

English

Lowland wetlands generally have a high agricultural production potential and can be local hot-spots for biodiversity. Specific seasonal wetland system is largely distributed in north-central Namibia. Seasonal wetlands consist of seasonal river wetlands (locally known as oshanas). However, studies on soil fertility, salinity and sodicity in seasonal river wetlands are still limited in this area. The objective of this study was hence to investigate the soil fertility status of seasonal wetlands and evaluate their potential for agricultural production and consider sustainability of the land use system. Soil samples were collected from 102 different spots of the flood plain within 3 major seasonal rivers, and analyzed for their physico-chemical properties and salinity and sodicity. The findings for average soil organic carbon (1.94 g kg-1) and average clay contents (102.3 g kg-1) of seasonal rivers were drastically lower than the wetland of semi-arid Africa regions (organic carbon, 5.8 g kg-1; clay contents, 340 g kg-1), and organic carbon and clay content significantly (p<0.05) decreased at the lower part of each seasonal river. Most of the seasonal river soil’s’ electrical conductivity of saturated paste extract (ECe) and the sodium adsorption ratio of the saturated paste extract (SAR) were more than 4 dS m-1 and 13, respectively. However, there were large differences in electrical conductivity of saturated paste extract (ECe) and the sodium adsorption ratio of the saturated paste extract (SAR) values among the sampling spots. These findings suggest the high agricultural importance to improve the soil organic matter and clay contents, and land selection to avoid the strongly high saline-sodic soil sites in seasonal river.   Key words: Seasonal flooded wetland soil, soil fertility, soil salinity and sodicity, sustainable land use. &nbsp

Bulk electrical conductivity as an indicator of spatial distribution of nitrogen and phosphorous at feedlots

The increasing demands of producing beef for domestic and international consumption is leading to the development of feedlots in Argentina. Unfortunately, the great amount of manure produces leachate of nitrates and other ions which may affect groundwater quality. The objective of this paper was to identify the spatial distribution of bulk electrical conductivity (ECb) of non-saturated zone and its association with variability of nitrates and bioavailable phosphorous, water content, topography and electrical conductivity of saturated paste extract (EC).The analysis of the impact was done at two pens with different time of confinement of the animals (Pen1 and Pen 2, with 16months and 7years of animal occupation, respectively). The initial exploration phase was done by electrical resistivity tomography (ERT) and electromagnetic induction (EMI) surveys were subsequently performed at a subarea for studying the spatial distribution of ECb. A grid of soil sampling up to 1m depth was done at the same subarea of the EMI survey. A geostatistical interpolation of data was performed in order to map ECb, water content, nitrogen, bioavailable phosphorous and EC.Anomalies of higher conductivity (between 6 and 10 times the background values) were found near the feedbunk and the water trough, being greater on soils with larger period of manure recharge. Water content, nitrogen of nitrates (N-NO3−), bioavailable phosphorous (Pavail.) and EC showed patterns of spatial distribution similar to ECb. These patterns are mainly associated with the runoff movement of water to the lower zones in the case of a steeper slope and the soil compaction as in the Pen 1. In the Pen 2, the patterns of spatial variability are similar for ECb and water content while anomalies of high ECb were found along an abandoned feedbunk. High values of N-NO3−, Pavail. and EC were found at this site. A longer period of manure recharge resulted in higher values of nitrogen and bioavailable phosphorous in soils.It may be stated that bulk electrical conductivity was a good spatial indicator of water, nitrogen and bioavailable phosphorous in sandy loamy soils in these pens for the investigation depth of 1m. The bulk conductivity seems to be primarily associated with water content which is the path of transport of ions through the porous medium. In all the cases, the major contents of nitrogen and bioavailable phosphorous in the soil were associated with high bulk electrical conductivity when water content was above an equivalent depth of water of 100mm. The soil moisture status should be taken into account before an electromagnetic exploration for detecting soil contamination. Regarding the impact on groundwater pollution, the proximity of the water table to the surface seems to be more influential than the animal stocking rate for a longer period.

Spatial variability of soil electrical conductivity in a small watershed on the Loess Plateau of China

Knowledge of soil electrical conductivity of saturated paste extract (ECe) pattern is important to effectively managing farmland and improving crop productivity. The objectives of this study were (1) to characterize the spatial patterns of ECe and electrical conductivity of saturated paste (ECs) and (2) to determine the factors that affect significantly in the estimation of soil ECe. Soil samples were taken at various soil depths (0.1, 0.2, 0.4, 0.6, and 0.8m) of 124 locations in a small watershed. Besides ECe and ECs, various soil, topographical, and vegetation properties were measured. Geostatistical techniques were used to characterize the spatial patterns of ECe and ECs. Ordinary least squares (OLS) and generalized least squares (GLS) models were used to perform multiple regression analyses between ECe and other properties. The OLS model belongs to a non-spatial regression, whereas the GLS model is a spatial regression which considers the autocorrelation in the residuals. Results showed that both ECe and ECs presented moderate variability at the watershed scale. The ECe presented weak to moderate spatial dependency, whereas the ECs presented moderate to strong spatial dependency. The ratio of ECe to ECs differed with soil texture, and it was greater for sand texture than for loam texture. A fair to moderate spatial agreement existed between ECe and ECs at all depths except for 0.2m, where ECe presented a more random distribution. Heteroscedasticity in the residuals between two land uses (grass land and shrub land) and autocorrelation in the residuals only existed at 0.4m soil layer where the GLS model did not improve significantly over the OLS model in terms of explaining variations in ECe. Electrical conductivity of saturated paste was the dominant factor in explaining ECe variation for all depths, while soil separate significant affected the estimation of ECe at 0.1m as well. It is concluded that ECs may be used as a surrogate for ECe especially for homogeneous soil textures. This would greatly reduce the work involved in ECe measurement due to the easier availability of ECs. Our study implies that ECe can be used as an index of soil fertility condition in this area. In addition, OLS model can be accurate enough to describe the relationships between ECe and other properties due to the absence of strong spatial dependency of ECe in this area.

Predicting ECe of the saturated paste extract from value of EC1:5

He, Y., DeSutter, T., Hopkins, D., Jia, X. and Wysocki, D. A. 2013. Predicting EC e of the saturated paste extract from value of EC 1:5 . Can. J. Soil Sci. 93: 585–594. Many laboratories appraise soil salinity from measurement of electrical conductivity of 1:5 soil to water extract (EC1:5) due to its simplicity. However, the influence of salinity on plant growth is mainly based on electrical conductivity of saturated paste extract (ECe), so it is necessary to convert EC1:5 to ECe in order to assess plant response. The objectives of this research were to develop models relating EC1:5 and ECe under four different 1:5 equilibration methods: (1) shaking, (2) shaking plus centrifuging, (3) stirring, and (4) a United States Department of Agriculture-Natural Resources Conservation Service (2011) equilibration method. One hundred soil samples, which were all derived from glacial parent materials in North Dakota, USA, were selected for this study. Non-transformed, non-transformed separated, ln-transformed, and exp...

Predicting ECe of the saturated paste extract from value of EC1:5

He, Y., DeSutter, T., Hopkins, D., Jia, X. and Wysocki, D. A. 2013. Predicting ECeof the saturated paste extract from value of EC1:5. Can. J. Soil Sci. 93: 585-594. Many laboratories appraise soil salinity from measurement of electrical conductivity of 1:5 soil to water extract (EC1:5) due to its simplicity. However, the influence of salinity on plant growth is mainly based on electrical conductivity of saturated paste extract (ECe), so it is necessary to convert EC1:5 to ECe in order to assess plant response. The objectives of this research were to develop models relating EC1:5 and ECe under four different 1:5 equilibration methods: (1) shaking, (2) shaking plus centrifuging, (3) stirring, and (4) a United States Department of Agriculture-Natural Resources Conservation Service (2011) equilibration method. One hundred soil samples, which were all derived from glacial parent materials in North Dakota, USA, were selected for this study. Non-transformed, non-transformed separated, ln-transformed, and exponential models were developed between EC1:5 and ECe. Non-transformed, simple linear regression models had obvious segments for all equilibration methods and the residual distributions varied. Therefore, data were separated at EC of 4 dS m-1 and a quadratic curvilinear model was developed for relating EC1:5 and ECe (r2 values ranged from 0.87 to 0.93) when ECe values were less than 4 dS m-1. Although the linear model was significant (P<0.05), soils having ECe greater than 4 dS m-1 had r2 values less than 0.61. Across all soils, the ln-transformed model had r2 values greater than 0.85, which was greater than the non-transformed or exponential models. By comparison of r2, RMSE, and relative percentage difference, the separated curvilinear model that was established when salinity is less than 4 dS m-1, and ln-transformed models were superior at predicting ECe from EC1:5 data compared to non-transformed and exponential models. These results indicate that across all equilibration methods ECe can reliably be predicted from EC1:5 data for soils from this region.

Measurement of soil salinity using electromagnetic induction in a paddy with a densic pan and shallow water table

Rice (Oryza sativa L.) has become a monoculture in the saline lands of the Ebro Valley, Spain. The studied farm has produced rice since the 1970s; one exception was 1999, which enabled us to map the soil salinity. The farm had lateral salinity variations mirrored by the development of rye grass (Lolium multiflorum Lam.) planted in 1999. Our objective is to prove the value of a non-deterministic method using electromagnetic induction (EMI) to map the salinity of the rootable layer in the unfavorable circumstances of a paddy having shallow saline and quasi-artesian water table underneath a continuous densic layer. From our EMI readings and soil sampling, we draw a map of the electrical conductivity of saturated paste extracts (ECe) of the upper soil layer (0–40 cm), with ECe ranging from 1.6 to 20.8 dS m−1 and a mean of 7.9 dS m−1. A main achievement was the establishment of an easy procedure not requiring either: (i) knowledge regarding the salinity of the water table or the relationships between EMI readings and the deep soil composition; or (ii) a normal distribution of the EMI readings or of the ECe; or (iii) assumptions about the physical dimensions of the EMI readings. Our procedure will allow ECe to be mapped on other similar salt-affected paddies, helping to decide if a paddy can be planted with alternate crops for production, weed control, or soil structure improvement.

Effects of an imbedded gravel–sand layer on reclamation of coastal saline soils under drip irrigation and on plant growth

Governmental goals for the development of new municipalities in areas of very saline soils near shorelines of the Bohai Gulf, in north China, include planting landscape trees and shrubs along streets and highways, and in parks in residential areas. The soils are saline because of the presence of shallow groundwater (45–138cm) with salinity levels of >24dSm−1. Prevention of upward water movement from the saline groundwater could be an important factor in facilitating reclamation of the soil above the water table, as well as the long-term sustainability of any reclamation that is achieved. The possibility of placing a 20-cm thick layer of gravel–sand at a depth of 80cm to block upward water movement was evaluated in a three-year field experiment conducted during 2009–2011. Soil salinity and growth of landscape plant species were measured. Irrigation water was the local deep groundwater with electrical conductivity of 1.7–2.1dSm−1 and SAR (sodium adsorption ratio) of 4.3mmolL−1. Results indicated that the extent of desalinization (the ratio of salt content leached to the initial salt content) for the imbedded gravel–sand layer (GL) was larger than that for the non-gravel–sand layer treatment (NGL). Less salt accumulated in the surface soil during winter in GL compared to NGL. The mean electrical conductivity of saturated paste extracts (ECe) were <5dSm−1 in root distribution zones (0–40cm) for NGL compared to 3dSm−1 for GL; the corresponding pH of saturated paste extracts (pHe) were 8.5 and 8.7. The influences of time, treatment and time×treatment on soil ECe and pHe were significant. At the end of the treatment, the salinity levels in root zones for both treatments were suitable for the growth of plants that were moderately sensitive to salinity (3–4dSm−1). The results provide theoretical and technological guidance for salt leaching and landscaping of highly saline lands located along the coast of the Pacific Ocean.

PHYTODESALINATION OF A MODERATELY-SALT-AFFECTED SOIL BY SULLA CARNOSA

The aim of this investigation was to evaluate the ability of the indifferent halophyte Sulla carnosa Desf. to desalinize a moderately-salt-affected soil. Seeds were sown on a fertile soil added or not with 1.5 g NaCl. kg−1. Analogous treatments without plantation (control and salinized) were also used. Plant culture was performed under greenhouse conditions in non-perforated pots containing 10 kg soil each and irrigated with non-saline tap water. After 80 days of treatment, shoots were harvested. Soil samples were also collected after division of soil column in each pot into two horizons. Our results showed that salt addition increased electrical conductivity of saturation paste extract (ECe) from 3.3 to 8.4 dS. m−1 and soluble sodium concentration from 0.32 to 1.15 g. kg−1 soil in the upper horizon. In the lower horizon however, Na+ concentration was quasi-constant and then ECe was less increased. Plant culture inversed this pattern of sodium accumulation and salinity. Its productivity and phytodesalination capacity in 80 days were 5.0 t DW. ha−1 and 0.3 t Na+. ha−1 (24% of the added quantity), respectively. Interestingly, sodium dilution within biomass (41.5–45.6 mg. g−1 DW) and the non-altered nutrition make this plant suitable for forage as second use after phytodesalination.