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 (c lay loam, silt loam, and sandy loam) were hydrolyzed with 1 M or 6 M H Cl 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 read ily hydrolyzed fraction should be a part of the bioreactive SOC. Highe r amounts of soluble SOC and N as well as CO2 were released from all s oils 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 t he initial 2 hours of hydrolysis, and then increased very gradually. T he amounts of CO2-C evolved correlated with the amounts of NH4-N relea sed during the acid hydrolysis (r = > 0.88). The ratio of SOC to solub le N was lower in 6 M HCl hydrolysate than in 1 M HCl. Hydrolysis of s oil by 1 M HCl for 4 h appeared to be a promising approach for estimat ing the more bioreactive pools of SOC and N.