Decay of organic matter, inappropriate use of nitrogenous fertilizers, and the removal of alkaline plant material from the field in cropping systems further accelerate soil acidification (Vieira et al. 2008). Some studies have shown that legumes increase soil acidification in pastures and arable cropping systems (Williams 1980; Burle et al. 1997). Acid production during carbon and nitrogen cycles is considered to be the most relevant in agricultural and pasture ecosystems (Helyar and Porter 1989). In non — polluted areas, soil acidification is mainly caused by the release of protons during the cycling of carbon, nitrogen, and sulfur in the soil-plant-animal system (Ulrich and Summer 1991). In a balanced system, carbon, nitrogen, and sulfur cycling processes are coupled and there is no generation of acidity. Perturbations such as uncoupling of nutrient cycles, accumulation of soil organic matter, leaching of nutrients (mainly NO3~) and the mobile exchangeable basic cations (Ca2+, Mg2+, K+, and Na+), and application of nitrogen fertilizers (which cause oxidation of NH4+ to NO3~) generate soil acidity. NO3~ is not strongly adsorbed by the soil and will leach, and if it is not totally taken up by the crop, increased soil acidification will occur as a consequence (Bolan and Hedley 2003).