Soil order and management practices control soil phosphorus fractions in managed wetland ecosystems

Abstract

Phosphorus, an essential element for plant and animal growth, can also impair water quality. Understanding management effects on P dynamics can aid in the management of these systems to reduce nonpoint source pollution and improve fertilizer use efficiency. A sequential P fractionation procedure was used to evaluate labile to recalcitrant inorganic (Pi) and organic (Po) fractions in wetland rice soils. In this study we evaluated 71 wetland soils in the Sacramento Valley, California, consisting of different soil orders (Alfisols, Entisols, Mollisols and Vertisols) and different management systems (conventional rice, organic rice and natural wetlands). Total soil P ranged from 165 to 784 μg g-1 and averaged 415 μg g-1. Mollisols contained significantly more Pi and Po than all other soils; especially more HCl-Pi and Po. Although most studies ignore Po in the HCl fraction, 9% of total P was recovered in this fraction, suggesting that this fraction should not be ignored in studies aimed at quantifying and understanding organic P. The HCl-Po fraction was closely correlated with HCl-Pi, suggesting that it may be Ca bound P. Soils managed under organic rice production had higher NaHCO3-Pi and NaOH-Pi levels than conventional rice systems; while the natural wetland systems showed intermediate amounts. Organic or synthetic P fertilizers applied in excess of the amount of P that is removed during harvest was recovered as NaHCO3-Pi and NaOH-Pi. © 2010 The Author(s).