Effect of low-molecular-weight organic acids on kinetics release and fractionation of phosphorus in some calcareous soil
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Effect of low-molecular-weight organic acids on kinetics release and fractionation of phosphorus in some calcareous soils of western Iran M. Taghipour & M. Jalali
Received: 17 June 2012 / Accepted: 15 October 2012 / Published online: 11 November 2012 # Springer Science+Business Media Dordrecht 2012
Abstract Organic acid has been related to nutrient mobilization, mainly in phosphorus (P) insoluble utilization, and therefore enhances P bioavailability. In this study, we examined the effect of low-molecularweight organic acids (malic, citric, and oxalic acids) on P release of some calcareous soils from western Iran. Fractionation and speciation of P in the soil solution were studied at the initial and final P release. Significantly different quantities of P were extracted by the organic acids. On average the maximum (1,554.9 mg kg-1) and the minimum (1,260.5 mg kg-1) P were extracted by 10 mM oxalic and malic acid, respectively. Power equation described well P release. In the initial stage of P release, the solution samples in soils were supersaturated with respect to hydroxyapatite and βTCP. At the end of P release, all solutions were undersaturated with phosphate minerals. The percentage of Fe-Al oxide fraction generally increased after P release, while carbonate and residual P fractions were decreased in all organic acids. Compared with the native soils, adding malic and citric acids had no effect on Fe-Al oxide fraction, but oxalic acid significantly reduced this fraction.
M. Taghipour : M. Jalali (*) Department of Soil Science, College of Agriculture, Bu-Ali Sina University, Hamadan, Iran e-mail: [email protected]
Keywords Phosphate . Organic acids . Fractionation . Release . Speciation
Introduction Phosphorus (P) is an essential nutrient element for plant growth. Calcareous soils are frequently characterized by the low availability of P for plant uptake due to the low solubility of P compounds present in soils at high pH and the formation of relatively insoluble complexes, e.g., Ca-P. Continued long-term application of fertilizers can lead to P fixation, low recovery, and accumulation in soil, thus increasing the potential for P loss to surface waters and eutrophication (McDowell et al. 2001; McDowell and Sharpley 2003). Many soils in Iran have received large amounts of P fertilizer and consequently contained high level of available P (Jalali 2007), and presence of P in groundwater in agricultural area in southern Malayer, western Iran was reported by Jalali (2009). The ability of the soil to release P into solution significantly affects on risk of P loss to overland and subsurface flow (McDowell and Sharpley 2003). The methods of 10 mM CaCl2 are widely used to determine the kinetics of P release in soil (Shariatmadari et al. 2006; McDowell and Sharpley 2003; Jalali and Ahmadi Mohammad Zinli 2011). The root exudation of organic acids has been suggested to increase P availability in calcareous soils. The most common low-molecularweight organic acids (LMWOAs) identified in soils include oxalic, succinic, tartar
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