Search

Aims: Our objective was to evaluate if the relationship between quick indices of mineralizable N and soil N mineralization potential (No) is affected by long-term fertilization with inorganic fertilizers (IF) and/or poultry litter (PL).Methods: Samples from four long-term research sites that were fertilized with IF, IF+PL, or PL (>10 years) were aerobically incubated for 24 weeks to determine No. Soil No was then related to the results from the Illinois soil test analysis (ISNT), extractions with hot KCl, NaOH, or phosphate-borate (PB), and an anaerobic incubation (Nan).Results: All evaluated chemical methods were correlated with No (R2 > 0.59). However, the models to describe the association between the chemical methods and No differed depending on the fertilizer treatment, due to the inability of chemical indices to estimate the No increase observed in some PL-amended soils. In contrast, the relationship between Nan and No was not affected by fertilization strategy.Conclusions: Chemical indices can lead to the underestimation of soil N mineralization potential in PL-treated soils when the indices are calibrated in IF-amended soils, whereas the biological method Nan predicted No independently from the field's fertilization history. [ABSTRACT FROM AUTHOR]

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 μm) of the soil. The aim of this study was to evaluate if P in 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 μm). 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 8.3 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. [ABSTRACT FROM AUTHOR]