Saline soils defined

Of the seven macro mineral elements required by dairy cattle, five can be considered fertilizer elements (potassium, calcium, phosphorus, magnesium, and sulfur), but sodium and chloride are both toxic lo plants at high concentrations and present practical problems in areas with saline soils. High salt intakes have also been shown lo increase udder edema in heifers. Because of the importance of chloride in nutrition and mclabolisni. research is needed to define the chloride requirements of lactating cows and clarify mineral relationships, especially between chloride and potassium plus sodium-... 

A distinguishing feature of a sabkha is the presence of salt. Normally the salinity of groundwater rapidly inereases in a landward direction, with the result that the creation of salt crystals, caused by evaporation and desiccation, can form relatively hard crusty surfaces. The salt encrusted surfaces are sufficiently strong and durable. They become impassable upon wetting from rainfall or storm tides. In general a soil with a salt content equal to or more than 0.3% can be defined as a saline soil (Naifeng 1994). Salt can also be transported by wind. 

To promote the use of poor quality water for irrigation, a field research study was conducted in three semi-arid regions with water scarceness in Syria in order to define, under field conditions, the wheat yield response function to irrigation water salinity, the effect of soil texture and structural characteristics on the irrigation water salinity threshold, and to compare this value with the conventional threshold value. 

In the first instance, the roots of planta may take up all substances in solution without selection. But this action is not one of simple imbibition as in the case of sponges. Liebig-, in a recent memoir, maintains that the spongioles, in obtaining their supply of saline matter, exert a real decomposing action on certain Ill-defined compounds, which the saline mattar forms with the. insoluble constituents of the soil, Those substances which are conveyed to planta in solution are retained in greater or less quantity, or are entirely rejected when not fit For assimilation. 

Surface water can be defined as any river, lake, stream, pond, marsh, or wetland as ice and snow and as transitional, coastal, and marine water naturally open to the atmosphere. Major matrix properties, distinguishing water types from each other, are hard and soft water, and saline and freshwater. Groundwater is typically defined as water that can be found in the saturated zone of the soil. Groundwater slowly moves from places with high elevation and pressure to places with low elevation and pressure, such as rivers and lakes. Partitioning interactions of the groundwater with the solid soil matrix is an important factor influencing the fate of toxicants. Physicochemical properties of water that may affect toxicity of chemicals in all water types are listed in Table 2.2. 

Salinity defines the concentration of ions dissolved in soil water, and is measured directly by electrical conductivity (EC). Soil water is held under tension or suction and as such is not available for analysis. To compensate for this, the standard procedure is to measure soil EC on a water extract. Soil scientists use what is called a saturated paste soil water extract (for more details see Radojevic and Bashkin, 1999). 

These considerations of the general behaviour of metals in aquatic and soil systems should be used to assess and control accumulation and mobilisation processes of trace metal ions. To evaluate the environmental impact of mining activities with regard to chemical contaminants, the following main steps of geochemical activities are recommended (1) estimate the extent of the local and regional contamination, (2) quantify the sources of heavy metals, chlorides, sulphates and thus the total acidity and salinity, as well as other contaminants and (3) define and control major sources, i.e. waste rock heaps, tailings, waste dumps and air pollution, etc. 

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