The objective of this work was to evaluate eight closed‐form unimodal analytical expressions that describe the soil‐water retention curve across the complete range of soil water contents. To meet this objective, the eight models were compared in terms of their accuracy (RMSE), linearity (coefficient of determination, R2, and adjusted coefficient of determination, R2adj), and prediction potential. The latter was evaluated by correlating the model parameters to basic soil properties. Retention data for 137 undisturbed soils from the Unsaturated Soil Hydraulic Database (UNSODA) were used for the model comparison. The samples showed considerable differences in texture, bulk density, and organic matter content. All functions were found to provide relatively realistic fits and anchored the curve at zero soil water content for the coarse‐textured soils. The performance criteria were similar when averaged across all data sets. The criteria were found to be statistically different between the eight models only for the sandy clay loam soil textural class. An analysis of the individual data sets separately showed that the performance criteria were statistically different between the models for 17 data sets belonging to six different textural classes. We found that the Khlosi model with four parameters was the most consistent among different soils. Its prediction potential was also relatively good due to significant correlation between its parameters and basic soil properties.
The present study aimed to evaluate the influence of environmental factors on essential oils (EOs) composition of Origanum compactum populations sampled all over the distribution area of the species in Morocco, and to determine the extent of the chemical profiles throughout the geographical distribution of the species. The chemical compositions were submitted to canonical correlation analysis and canonical discriminant analysis that indicated a significant relationship between oil components and some environmental factors. According to their chemical composition and edapho-climatic characteristics, two major groups of populations were differentiated. The first group was composed of samples growing in regions with humid climate, clayey, sandy, and alkaline soils. These samples showed high thymol, α-terpineol, linalool, and carvacryl methyl oxide content. The second group consisted of plants belonging to semi-arid climate, and growing at high altitudes and silty soils. These samples were characterized by high carvacrol, α-thujene, α-terpinene, and myrcene content. However, populations exposed to sub-humid climate, appeared less homogeneous and belong mainly either to the first or second group. A significant correlation between some edaphic factors (pH, K O content, soil texture) and the EOs yield of O. compactum plants was evidenced. In spite of the correlation obtained for the oil composition with edapho-climatic factors and the variance explained by the environmental data set, the observed EO diversity might be also genetically determined.
1 2 Irrigated agriculture is threatened by soil salinity in numerous arid and semiarid areas of the Mediterranean 3 basin. The objective of this work was to quantify soil salinity through electromagnetic induction (EMI) 4 techniques and relate it to the physical characteristics and irrigation management of four Mediterranean 5 irrigation districts located in Morocco, Spain, Tunisia and Turkey. The volume and salinity of the main water 6 inputs (irrigation and precipitation) and outputs (crop evapotranspiration and drainage) were measured or 7 estimated in each district. Soil salinity (EC e ) maps were obtained through electromagnetic induction surveys 8 (EC a readings) and district-specific EC a -EC e calibrations. Gravimetric soil water content (WC) and soil 9 saturation percentage (SP) were also measured in the soil calibration samples. The EC a -EC e calibration 10 equations were highly significant (P < 0.001) in all districts. EC a was not significantly correlated (P > 0.1) with 11 WC, and was only significantly correlated (P < 0.1) with soil texture (estimated by SP) in Spain. Hence, EC a 12 mainly depended upon EC e , so that the maps developed could be used effectively to assess soil salinity and 13 its spatial variability. The surface-weighted average EC e values were low to moderate, and ranked the 14 districts in the order: Tunisia (3.4 dS m
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