Organic amendments affect phosphorus sorption characteristics in a paddy soil

Continuous excessive application of phosphorus (P) fertilizer and/or manure in areas with intensive agriculture can lead to an accumulation of P in soils and progressive saturation of soil sorption capacities, thus resulting in increased P loss from soil to aquatic ecosystem. An 8-year field experiment with four fertilization patterns (chemical fertilizer only, fertilizer plus straw, fertilizer plus 7.5 t ha(-1) manure, and fertilizer plus 15 t ha(-1) manure) was conducted in the Taihu Lake region of eastern China to investigate the effects of incorporation of straw and manure on P accumulation and the changes of P sorption capacity of a paddy soil. Degrees of P saturation, contents of Olsen-P and total P in manure treated soils were significantly higher than those treated with fertilizers alone or with straw retention (P<0.05). Phosphorus accumulation in studied soil was less labile in straw treatment than in manure treatments, but it remained extractable by ammonium oxalate. The Langmuir P sorption maximum (S-max) ranged from 24.7 mmol kg(-1) to 43.2 mmol kg(-1), and was highly correlated with oxalate extractable Al (Al-ox, r=0.85) and Fe (Fe-ox, r=0.79). Moreover, path analysis showed that the direct effect of Al-ox on S-max was significant (P<0.05) while that of Fe-ox on S-max was insignificant; and that Al-ox could also exert influence on S-max via its indirect effect through Fe-ox and organic matter. Thus, Al was the most important soil property associated with S-max in the paddy soil based on path analysis results. (C) 2013 Elsevier B.V. All rights reserved.