|M.Sc Student||Master Yigal|
|Subject||Transformations and Gaseous Losses of Nitrogen from Effluent|
|Department||Department of Agricultural Engineering||Supervisor||Professor Emeritus Abraham Shaviv|
Effluent irrigation is a must in Israel, however it has the potential to interfere with soil N transformations. The research studied the influence of effluent irrigation on soil N transformations and gaseous N (N2+N2O+NH3) losses. The measurement of N2 and N2O fluxes, the assessment of the N2O sources and the quantification of the gross rates of various N transformations (in field and laboratory studies) was made possible by application of 15N labelled fertilizer and the characterization of an isotopic composition of the evolved gases using Isotope Ratio Mass Spectrometry.
Significant quantities of N2 and N2O (up to 3.9% of the applied fertilizer) were emitted when soils were saturated. The N losses were negligible at lower moisture contents. Effluent induced N2 and NH3 losses in the short term. No unequivocal effluent effect as to N2O losses was observed. Plants were shown to stimulate N2O emissions. Nitrification was the major source of the N2O evolved, however denitrification was the dominant process at higher moisture contents.
Very high nitrite levels were observed in effluent irrigated soils and nitrification was shown to be its main source. Changes in microbial population structure and free NH3 concentrations were postulated to explain this phenomenon. A simplified two-stage nitrification model tested these assumptions and could satisfyingly predict the behavior of all mineral N species.
Mineralization in the grumosol soil was found to have a potential supply of up to 30% of the applied fertilizer. The highest contribution of potentially mineralizable organic N was found to be in the native soil and not in the applied effluent. Nitrification was in some cases encouraged by effluent application. There were differences in the mineralization and nitrification kinetics between fresh water and effluent irrigated soils.