Plant available N supply and recalcitrant C from organic soil amendments applied to a clay loam soil have correlations with amendment chemical composition

- PAN and C outcomes from organic amendments in the soil varied widely.
- HWOC:HWN ratio, total N, and 13C NMR ratios highly correlated with PAN.
- (Aromatic C (110-165 ppm shift)/total C) of waste-correlated with soil C.
- Predictive success more likely if work focuses on discrete classes of organics

A 49 week soil incubation study employing 15 recycled organic (RO) wastes was conducted to investigate relations (through Kendall correlation analysis) between plant available nitrogen (PAN) supply and soil recalcitrant carbon (C) parameters with those of the RO waste chemical properties as determined by wet chemistry and spectroscopic methods. The hot water extractable organic C to hot water extractable nitrogen (N) ratio (HWOC:HWN ratio) was often the highest correlating property for mineral N supply (mg mineral N kg dry waste− 1), while many of the 13C NMR functional group parameters such as the aromatic C to N ratio, phenyl C to N ratio, and aryl C to carbonyl C ratio were also significantly correlated with mineral N supply. These functional group C properties were significantly correlated with mineral N release in the later phase of the incubation (i.e. 12-49 weeks), while HWOC:HWN ratio was highly correlated with the early period (0-2 weeks) but this period had a dominant influence on the total supply. The fore mentioned 13C NMR functional group properties were also significantly correlated with recalcitrant C, but the fraction of total RO waste C as aromatic C (110-165 ppm) was the parameter most highly correlated with this property. Molecular C component composition had no predictive advantage over functional group data. Future work should focus on narrow classes of organic amendments for predictive correlations.