|M.Sc Student||Rinot Oshri|
|Subject||Hot Water Extraction for Rapid Characterization of Changes|
in Organic Carbon and Nitrogen Formations in
|Department||Department of Civil and Environmental Engineering||Supervisors||Professor Emeritus Abraham Shaviv|
|Professor Emeritus Michal Green|
|Full Thesis text - in Hebrew|
Irrigation with treated wastewater (effluent) has an influence on the microbial population, organic matter quality and quantity and nitrogen dynamics in soil.
Hot water extraction is a useful method for detecting changes in soil labile organic matter, induced by different land uses and soil amendments/fertilizers. Hot water extractable nitrogen was found indicative of the availability of organic N.
EEM (excitation-emission matrix) fluorescence spectroscopy has been widely used as a method for characterizing dissolved organic matter in water and soil solutions and extracts.
Samples from five different agricultural soil types in Israel were collected from long-term experiments in which effluent and fresh water irrigation was compared. The extraction procedure was cold water extraction (CaCl2 0.01M, 20ºC, 1 hr) followed by hot water extraction (CaCl2 0.01M, 80ºC, 16 hr). TOC (Total organic Carbon), TN (Total Nitrogen) and mineral N-species concentrations were measured in the cold and hot water extractions. Organic Nitrogen availability (mineralizable N) was also estimated by aerobic incubation of soil samples for five weeks.
The water extracted solutions were characterized using a fluorometer. PARAFAC (Parallel Factors Analysis) was used for interpreting the EEM data, by looking for the main components of the organic compounds. In addition, N-PLS was tested as a method for prediction of TOC, TN and TON concentrations from EEM data.
The quantitative results emphasize the effectiveness of hot water extraction in detecting differences in concentrations of major organic carbon and nitrogen components in effluent and fresh water irrigated soils. In general, as excepted, extracted organic matter concentrations were higher in effluent irrigated soils. Mineralized N was also usually higher in effluent irrigated soils. Moreover, hot water extractable nitrogen was found to be a good predictor for nitrogen availability.
Three main components were found by PARAFAC modeling of the EEM data of the hot water extractions, related to humic acid, fulvic acid, and protein. The scores calculated for the humic and fulvic components were highly correlated with hot water TOC, TN and TON concentrations. Prediction of these parameters was improved by the N-PLS method. Other spectroscopic results indicate possible differences in extractable organic matter characteristics between treatments and different soil types. The scores calculated for the fulvic component in the PARAFAC model were correlated with mineralizable-N in all soils. The obtained results provide encouraging indications about the potential of using hot water extractions and spectroscopy for characterizing important components of soil carbon and nitrogen in different soils.