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United States Department of Agriculture

Agricultural Research Service

Title: Characterization of Organic Carbon and Nitrogen in Soil by Acid Hydrolysis.

Authors
item Xu, J - UNIVERSITY OF MINNESOTA
item Cheng, H - UNIVERSITY OF MINNESOTA
item Koskinen, William
item Molina, J.A.E. - UNIVERSITY OF MINNESOTA

Submitted to: Nutrient Cycling in Agroecosystems
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 22, 1996
Publication Date: N/A

Interpretive Summary: Soil is an important source and sink of active carbon and plays a major role in the global carbon cycling. The increasing concern about greenhouse gas emission and global climate change has led to demand for better estimates of global carbon pool, especially the bioreactive soil organic carbon (SOC) fraction. The bioreactive SOC fraction consists of living and dead organic materials subject to rapid biological decomposition. This fraction is a direct reservoir of soil nutrients as well as the dominant driving force of nutrient availability. The organic chemicals entering soil environments are distributed in both bioreactive and stable SOC pools due to the interaction between the chemical and soil organic matter. Current SOC fractionation methods are not designed to differentiate and measure the magnitude of the bioreactive pool; none of these methods are able to successfully assess and isolate the entire bioreactive SOC pool. A potential approach for assessing the pool of bioreactive SOC could be acid hydrolysis. Hydrolyzing soil with 1 M HC1 for 2 to 4 h appears to provide a promising approach for evaluating the pool of bioreactive SOC. The experimental results can be compared with model estimates of bioreactive OC pool and other fractionation approaches to define this pool. Researchers will now be able to make better estimates of the global carbon pool.

Technical Abstract: Studies were conducted to determine the potential of acid hydrolysis for estimating the bioreactive fraction of soil organic carbon (SOC) in soils. Three soils (clay loam, silt loam, and sandy loam) were hydrolyzed with 1 M or 6 M HC1 under reflux for up to 24 h. Results showed that 1.7 to 3.2 percent of OC could be liberated as CO2 from the acid hydrolysis of soil, which should be a part of the bioreactive SOC. Higher amounts of soluble OC and N as well as CO2 were released from all soils by 6 M HC1 than by 1 M HC1. Soluble OC and N contents in both 1 M HC1 and 6 M HC1 hydrolysates of all soils increased rapidly during the initial 2 hours of hydrolysis, and then increased gradually. The amounts of CO2-C evolved correlated with the amounts of NH4-N released during the acid hydrolysis (r= greater than 0.88). The ratio of OC to soluble N was lower in 6 M HC1 hydrolysate than in 1 M HC1. Hydrolysis of soil by 1 M HC1 of 4 h appeared to be a promising approach for estimating the more bioreactive pools of SOC and soil N.

Last Modified: 7/28/2014
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