Phosphorus in the coarse soil fraction is related to soil organic phosphorus mineralization measured by isotopic dilution

A sound prediction of soil organic phosphorus (P-o) mineralization would be helpful to improve fertilizer recommendations. However, in most mineral soils expensive and time consuming isotopic dilution experiments are required to assess P-o mineralization. A proposed method to estimate P-o mineralization is the quantification of P in the coarse fraction (CF, >53 mu m) of the soil. The aim of this study was to evaluate if Pin the CF can effectively predict P-o mineralization. Soil samples from three North American long-term arable field experiments (>10 years) with different textures (sand content 15-82%) and different fertilization treatments (non-P-fertilized, mineral P fertilizer, poultry litter) were analyzed. Soil samples were physically fractioned into CF and fine fraction (FF, <53 mu m). Total P (P-t), P-o, and total carbon (C-t) were determined in each fraction. Gross and net P-o mineralization rates as well as soil respiration were determined in a 13-day-incubation experiment. The cumulative gross P-o mineralization over 13 days ranged from 83 to 38.6 mg P kg(-1), while P-t in CF varied between 9.7 and 90.7 mg P kg(-1) and P-o in CF between 6.1 and 17.7 mg kg(-1). No association between P-t in CF and gross or net mineralized P-o was observed. However, a significant linear relationship between P-o in CF and net (R-2:0.68, p < 0.01) and gross mineralized P-o (R-2:0.72, p < 0.01) was observed after 6 days and 13 days of incubation. Additionally, gross and net mineralized P-o could also be predicted from C respiration, and these models were significantly improved by incorporating the C-t:P-o ratio of the CF. Our results suggest that the quantification of P-o in the CF as well as the measurement of respiration corrected by the C-t:P-o ratio of the CF are promising non-isotopic indicators of P-o mineralization rates. (C) 2016 Elsevier Ltd. All rights reserved.