Carbon and Nitrogen Mineralization Rates after Application of Organic Amendments to Soil

TLDR

The study aimed to quantify carbon and nitrogen mineralization rates from various organic amendments differing in total C/N content and quality to better understand their impact on the soil nitrogen cycle. The authors incubated five amendments—pelletized poultry manure, two green‑waste composts, a straw compost, and vermi‑cast—in coarse‑textured soil at 15 °C for 142 days, measured CO₂ evolution with alkali traps, and calculated gross N mineralization via ¹⁵N isotopic dilution, while assessing amendment C quality by chemical analysis and ¹³C NMR. Amended soils exhibited higher CO₂ evolution and gross N mineralization than control, with most amendments releasing sufficient inorganic N to justify reduced fertilizer use; pelletized poultry manure released the most N, indicating a need to lower its application rate, and CO₂ evolution correlated strongly (R² = 0.95) with N mineralization, while certain chemical C‑quality metrics correlated with cumulative C and N release but ¹³C NMR groupings did not.

Abstract

ABSTRACT The objective of this study was to quantify C and N mineralization rates from a range of organic amendments that differed in their total C and N contents and C quality, to gain a better understanding of their influence on the soil N cycle. A pelletized poultry manure (PP), two green waste–based composts (GWCa, GWCb), a straw‐based compost (SBC), and a vermi‐cast (VER) were incubated in a coarse‐textured soil at 15°C for 142 d. The C quality of each amendment was determined by chemical analysis and by 13 C nuclear magnetic resonance (NMR). Carbon dioxide (CO 2 –C) evolution was determined using alkali traps. Gross N mineralization rates were calculated by 15 N isotopic pool dilution. The CO 2 –C evolution rates and gross N mineralization rates were generally higher in amended soils than in the control soil. With the exception of GWCb all amendments released inorganic N at concentrations that would be high enough to warrant a reduction in inorganic N fertilizer application rates. The amount of N released from PP was high indicating that application rates should be reduced, or alternative amendments used, to minimize leaching losses in regions where ground water quality is of concern. There was a highly significant relationship between CO 2 –C evolution and gross N mineralization ( R 2 = 0.95). Some of the chemically determined C quality parameters had significant relationships ( p < 0.05) with both the cumulative amounts of C and N evolved. However, we found no significant relationships between 13 C NMR spectral groupings, or their ratios, and either the CO 2 –C evolved or gross N mineralized from the amendments.