טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentKremen Arie
SubjectSimulating Nitrogen Transformations in Effluent Irrigated
Soils Containing Aggregates
DepartmentDepartment of Agricultural Engineering
Supervisors Professor Uri Shavit
Professor Emeritus Abraham Shaviv
Professor Emeritus Jacob Bear


Abstract

Effluent irrigation is known to enhance gaseous nitrogen losses via ammonia volatilization, nitrification, and denitrification. To study the effects of effluent irrigation on nitrogen (N) transformations, a dual porosity model has been formulated, in which the soil matrix (macropores) contains homogeneously distributed spherical, uniformly sized aggregates (micropores). Aggregates are assumed to remain water saturated with immobile water, while unsaturated water flow and reactive transport occurs in the macropores. Diffusion describes mass transport across the macropore/micropore interface and reactive diffusion is the dominant process within the aggregate. Diffusive constraints together with respiratory activity have been shown to be the major cause leading to the establishment of anaerobic conditions within aggregates even while macropore oxygen availability remains non-limiting. The major factors influencing the development of anaerobic conditions within aggregates were its size and the soil respiration rate.  Incremental oxygen demand for organic carbon (C) and nitrogen mineralization were found to be negligible. The aggregate sub-model was employed to study the effects of diffusive constraints on aerobic nitrogen transformations, the occurrence of coupled nitrification denitrification, and the appearance of nitrite during coupled nitrification/denitrification.   Employing the complete dual-porosity model, the fate of C & N compounds in soils with and without aggregates were compared, subject to freshwater and effluent irrigation.  Enhanced water holding capacity of effluent irrigated soils has been shown to increase gaseous nitrogen losses.    Although the presence of aggregates enhances the overall production of N2, it accumulates in the soil and is gradually released to the atmosphere.