This investigation was initiated to assess the following objectives: (1) to measure the total calcium and magnesium content in agricultural soil and sewage sludge from the Mediterranean coastal area of Motril (southeastern Spain); (2) to determine the pH values of indicated samples in order to
IntroductionCalcium is readily evident in alkaline soil and is very scarce in very acidic silicon soil. Weathering and rainfall in the area has a large impact on the chemical composition and calcium levels in the surrounding soil. In soil from arid or semiarid zones, high calcium concentrations have been found (Ganor and Mamame, 1982; Löye-Pilot et al., 1986;Young et al., 1988). Lower levels of acidity, less rainfall, and therefore less erosion, enhance the stability of minerals like the calcium in the soil's clay. As a result, the high calcium content will tend to flocculate in the upper profile of the soil's clay (Ruhe, 1984). Phillips and Chiy (2002), after applying sodium fertilizers, observed an enhancement of calcium concentrations in leachate. Similarly, an increase in calcium, magnesium, and pH values was observed in tropical agricultural soil after applying compost (Slattery et al., 2002;Soumare et al., 2003).In soil, magnesium is present mainly in inorganic compounds, although considerable amounts also appear associated with the organic material in humus (Sutcliffe and Baker, 1983). It is known that the principal portion of exchangeable magnesium is associated with clay particles. Exhaustion of the soluble magnesium cation in the soil by microorganisms and the plant's roots provokes uptake of the solid (non-soluble) mineral, which affects the nonexchangeable fraction. On the other hand, when the soil's acidity increases, a diminishment of available magnesium is observed due to the fact that hydrogen ions occupy a high number of the exchange sites (Sutcliffe and Baker, 1983). Studies indicate that in coastal areas magnesium enters the atmosphere from the sea because this element is one of the main constituents of marine aerosols.It is known that magnesium uptake by plants is affected by the presence of other cations such as ammonium, potassium, manganese, and sulphur (Pessarakli, 1995; Phillips and Chiy, 2002). For high levels of pH, the ratios of Mg/Ca, Mg/K and Mg/Al, rather than the magnesium concentration alone, are related to the element flux in plants (Rengel and Robinson, 1990).The existence of calcium and magnesium in soil is related to several factors, including geographic location, type of rock, pH, nature of drainage water, clay content, cation exchange capacity, weathering and climatic conditions, and type of plant grown (Young et al.,
