Modeling of fertilizer transport through soil, case study: Nile Delta

Abstract

Egypt’s population is estimated at 90 million people. Egypt covers an area of 1,001,449 km2 that is mostly desert (Sahara). Only 6% of Egypt’s area is inhabited. Most of the people live in the Nile Delta and the narrow Nile Valley. The majority of Egyptians (43.3%) live in Lower Egypt (north of the country), whereas 37.1% live in Upper Egypt (south). The total agricultural land area in Egypt is about 3.85 million ha, accounting for almost 3.5% of the total area. Only 5.4% of the land resources in Egypt are qualified as excellent, and the rest is either poor or of low quality (mainly due to salinity problems). The total area cropped annually increased from 4.6 million ha in 1982 to 6.5 million ha in 2003 due to increased cropping intensity, till it reached 6.9 million ha (16.5 million feddan) in year 2009. That is because of the variety between annual and permanent crops which made it possible to permit up to three harvests per year. In this chapter, the description of Nile Delta was presented including geography, climate, and geology. The types and physical properties of groundwater aquifers including the Nile Delta aquifer were covered. The principles of groundwater contamination with organic and inorganic contaminants including nutrients such as nitrogen, phosphorous, and sulfur were illustrated. The physicochemical reactions (hydrolysis, oxidation–reduction, biodegradation, adsorption, and volatilization) are described in detail. In addition, information about the agroecological zones and farming systems, particularly in regard to agricultural suitability, was provided. The agricultural production systems, including fertilizer requirements and crop needs, were also described. The recommended rates of fertilizer for the main crops in Egypt were given. Besides, the summarization of several studies, results for the determination of the most suitable time and proper method of fertilizer application on various crops are supplied. On the other hand, the advection–dispersion equation which describes the contaminants transport process is presented with illustration for the advection, dispersion, and adsorption phenomenon. Different numerical models including finite difference method (FDM), finite element method (FEM), and boundary element method are covered. Also, the most popular computer codes Modular Finite-Difference Groundwater Flow Model (MODFLOW), MT3DMS, Groundwater Modeling System (GMS), Soil and Water Assessment Tool (SWAT), Finite Element Subsurface Flow and Transport Simulation System (FEFLOW), and HYDRUS are presented. Moreover, the groundwater modeling systems (MODFLOW and MT3DMS) are used to simulate three-dimensional groundwater flow and NO3− transportation processes in El-Menoufia Governorate as a case study, located in the central region of the Nile Delta aquifer. The results highlight areas of groundwater contamination by NO3−, which occurred at 40 m depth because of the significant loads and method of nitrogen fertilizer application.