Carbon mineralization and retention of livestock manure composts with different substrate qualities in three soils

Purpose: Since substrate quality can influence the C mineralization pattern of compost in soils, proper selection of compost is important in increasing soil organic carbon (SOC) levels. This study investigated the effect of substrate quality of livestock manure composts on compost C mineralization and retention in soils. Materials and methods: A laboratory incubation experiment using four livestock manure composts (with different degrees of stability and other substrate qualities) and three soils (Inceptisol, Ultisol, and Andisol) was conducted for 100 days. Emission of CO₂ from the compost-amended soils was periodically measured and cumulative CO₂ emission was calculated as the percentage of total organic C (TOC) of applied compost (%C_cum). The %C_cum patterns were fitted with a double exponential first-order kinetics model to obtain the mineralizable C pool size and potentially retainable C in the soils. Results and discussion: The compost stability degree (SD) ranged from 31. 4 to 61. 5%, indicating a wide range of recalcitrance to microbial decomposition in the four composts used in our study. Among other compost quality indices, the K₂SO₄ extractable organic C concentration and molar ratio of NH₄⁺/NO₃^- decreased with increasing SD values. The %C_cum ranged from 1. 6 to 11. 4% and decreased as SD increased, suggesting that compost C mineralization in soils can be predicted using SD. The pool size (rapid pool + slow pool) of mineralizable organic C estimated using a first-order kinetic model ranged from 1. 7 to 28. 5% and tended to decrease with increasing SD. Among the three soils, Andisol showed relatively low %C_cum and mineralizable C pool size due to its inherent SOC protection mechanism via Al-organic matter complex. Conclusions: Our results suggest that application of compost with high SD and low extractable organic C would be more efficient in increasing SOC level due to a higher retention of compost C in the soils. The different patterns of C mineralization and retention among the three soils also suggest that not only compost quality but also soil characteristics should be considered when estimating CO₂ emission from compost-amended soils.