Characterization of potentially bioreactive soil organic carbon and nitrogen by acid hydrolysis

Studies determined the potential of acid hydrolysis for estimating the bioreactive fraction of organic carbon in soils (SOC). Three soils (clay loam, silt loam, and sandy loam) were hydrolyzed with 1 M or 6 M HCl under reflux for up to 24 h. Results showed that 1.7 to 3.2% of SOC could be liberated as CO2 from the acid hydrolysis of soil. This readily hydrolyzed fraction should be a part of the bioreactive SOC. Higher amounts of soluble SOC and N as well as CO2 were released from all soils by 6 M HCl than by 1 M HCl. Soluble SOC and N contents in both 1 M HCl and 6 M HCl hydrolysates of all soils increased rapidly during the initial 2 hours of hydrolysis, and then increased very gradually. The amounts of CO2-C evolved correlated with the amounts of NH4-N released during the acid hydrolysis (r = > 0.88). The ratio of SOC to soluble N was lower in 6 M HCl hydrolysate than in 1 M HCl. Hydrolysis of soil by 1 M HCl for 4 h appeared to be a promising approach for estimating the more bioreactive pools of SOC and N.