A N‐dynamics Model for Predicting N‐behavior Subject to Environmentally Friendly Fertilization Practices: II –Numerical Model and Model Validation (original) (raw)
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The 12th conference of Misr Society of Agricultural Engineering. Faculty of Agriculture, Alexandria University, Alexandria, Egypt.
The agro-chemicals present in the unsaturated soil are convected downwards by the declining perched water table after the cessation of the furrow surface irrigation, and thereby may pollute the freshwater aquifer. Finite difference approximation of the water flux and solute transport equations were conducted. In order to simplify the solute transport simulation, the numerical dispersion was used instead of the physical diffusion and dispersion. A field experiment was carried out to verify the presented model through the unsaturated soil in presence of shallow water table under eighteen different levels of soil compaction and to assess the risk of groundwater pollution due to the leaching of fertilizer solutes. An experimental plot was developed for this study. The field compaction control and the infiltration characteristics were measured to develop the constants of moisture release function and soil hydraulic conductivities. In order to explore the dynamics of the nitrogen leaching, two types of nitrogenous fertilizers were applied in three different doses and they were displaced by applying a constant depth of water in the furrows. Leachates from the soil-water samplers, and the water samples from the observation piezometers as well as absorbed and solution phase of nitrogen concentrations at different soil depths were collected and were subject to chemical analysis. The parameter represented the exchange characteristics of absorbed and solution phases of NH 4 and NO 3 with studied soil were predicted form the experimental field. The present study revealed that the developed model highly predicted the water and solute transport through the unsaturated soil with highly sensitive to any changes in compaction levels, initial water content, water table, solute application rate and fertilizer type. Carefully selecting the nitrogen fertilizer source was recommended to decrease the leachate concentration and increased the effected time. The results indicated that increasing the soil compaction level from 1.37 to 1.59 Mg/m 3 , decreased the leachate concentration by 83.4%. Moderate level of soil compaction may be leaded to decrease the leachate concentration and consequently decreased the pollution of the ground water. Future, long-term studies on a macro-scale are recommended to develop strategies for controlling or avoiding nitrate contamination.
Simulation of soil nitrogen dynamics using the SOILN model
Fertilizer Research, 1991
A model dealing with transport and transformations of nitrogen in soil is briefly described. The model has a one-dimensional layered structure and considers processes such as plant uptake, mineralization/ immobilization, leaching and denitrification. A soil water and heat model provides daily values for abiotic conditions, which are used as driving variables in the nitrogen simulation. In this study, the model was run with data from a polder-soil area in the Netherlands, with winter wheat as the crop. The simulation results showed that if a measured time course of crop nitrogen uptake throughout the growing season is available, mineral-N dynamics in soil can be satisfactorily described with this model. The main problems identified in the simulations were related to the partitioning between above-and below-ground plant-N, and supplying the crop with sufficient N, as given by the measurements.
Ecological Modelling, 2017
In the subsurface drainage system, there is a high potential for nitrate leaching, causing the pollution of both surface and ground water. In this research, a simple but comprehensive process-based model was developed for simulating the water flow and nitrogen dynamics. Processes considered in this model included all the important processes involved in nitrogen transformations, as well as nitrogen transport. Nitrogen transformation processes comprised fertilizer dissolution, nitrification, denitrification, ammonium volatilization, mineralization and immobilization. The nitrogen transport processes included nitrogen uptake by the plant, soil adsorption, upward flux, surface runoff losses and drain losses in the fields with the drainage network. For model evaluation, the measured data obtained from Imam agroindustrial Company, in Khuzestan, Iran, were used. Computed RMSE of the simulated water table, the drainage discharge rate, nitrate and ammonium concentration in drainage water were determined to be 14.58 cm,1.82 mm/day,1.73 mg/L and 0.48 mg/L, respectively. The results indicated a good agreement between the observed and simulated data. This model could be, therefore, used for fertilizer management, thereby reducing the concentration of nitrate and ammonium in the drainage water and helping to prevent the environmental pollution.
Modelling nitrogen dynamics in a plant-soil system with a simple model for advisory purposes
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A simple functional computer model for advisory purposes is described. Results of simulation indicate some limitations of the model especially in handling the water regime in soils with fluctuating water tables. A major problem seems to be the 'disappearance' of fertilizer N. Measurements by the fumigation-extraction method of microbial N during the growing season show that disappearance of fertilizer N can partly be explained by immobilization by the microbial biomass.
Two-dimensional Simulation of Nitrate Transport in an Agriculture-intensive Region
A two-dimensional steady-state solute transport model is developed to simulate movement of non-point sources of pollution in anisotropic porous media. The migration of chemicals dissolved in groundwater is governed by advective-dispersive processes which are also affected by the velocity of the flowing groundwater. Therefore, groundwater flow equation is solved for hydraulic gradient and hydraulic conductivity to approximate the average linear velocity of the fluid. The advection-dispersion is used to approximate the spatial and temporal distribution of non-reactive dissolved chemical in a flowing groundwater. A computer code is developed in MATLAB to solve the groundwater flow and solute transports equations by finite difference methods. The developed program is verified with soil-tank experimental data. The solute transport model is used to simulate non-point source of nitrate pollution in an agriculture-intensive region. Finally, the model outputs are analyzed to understand the f...
Nitrogen dynamics in flooded soil systems: An overview on concepts and performance of models
Journal of the Science of Food and Agriculture
Extensive modelling studies on nitrogen (N) dynamics in flooded soil systems have been published. Consequently, many N dynamics models are available for users to select from. With the current research trend, inclined towards multidisciplinary research, and with substantial progress in understanding of N dynamics in flooded soil systems, the objective of this paper is to provide an overview of the modelling concepts and performance of 14 models developed to simulate N dynamics in flooded soil systems. This overview provides breadth of knowledge on the models, and, therefore, is valuable as a first step in the selection of an appropriate model for a specific application.
Mathematical Models of Water and Solute Transport in Soil
Journal of Applied Solution Chemistry and Modeling, 2017
Improved understanding of water flow and solute transport through the unsaturated zone is important for the sustainable management of soils. As soils are complex and heterogeneous systems, quantification of the transport processes is difficult. More knowledge on the relationship between solute transport process, soil structure, hydrologic initial and boundary conditions, and observation scale is needed here.Modeling unsaturated flow and transport with mathematical or numerical methods is an important tool for predicting the infiltration and redistribution of soil water and the transport of solutes in the unsaturated zone. Flow and transport models are commonly used to support the decision making process in agricultural management, environmental impact assessment, toxic waste control, remediation design, and subsurface cleanup monitoring. The movement of contaminants through porou media describs by the combination of advection, diffusion-dispersion and chemical retardation. The most common model that describes solute transport by convection and dispersion is the convection-dispersion equation (CDE). This equation describes the change in concentration at any point along the flow path as a function of time. This paper is mainly dedicated to a discussion of basic processes for modelling of water flow and contaminant transport in saturated and unsaturated soils. After a brief description of the classical approach for simulating water flow and solute transport in porous media, issues related to water and solute trasport equation in soil.
Procedia Technology, 2016
Effective irrigation practices have become an optimal means of providing water and nutrients to crops as well as preventing the vulnerability of ground water contamination. This could be achieved by understanding the fate and transport processes of nitrogen compounds in the subsurface. However, nitrogen dynamics in the plant rhizosphere is very complex, which depends on many factors such as soil temperature, pH, water content, soil microbes, soil type and plant characteristics and cannot be easily quantified. Using state-of-the-art modelling techniques, an attempt was made to evaluate the reactive transport of ammonium nitrogen under continuous and alternate wetting and drying mode (AWD) of irrigation in soil columns using a HYDRUS 2D model. The model quantifies the soil sorption, microbial transformations such as nitrification and denitrification, leaching, and final release to aquifer for ammonium and nitrate input fluxes. This quantification helped in designing an optimal fertigation and irrigation schedule. Soil column study was done with variable saturation and in a combined unsaturated (45 cm) and saturated (5 cm) representing vadose and aquifer. Drip irrigation with wastewater containing 100 mg/L of ammonium and 500 mg/L of organic carbon (acetate) was applied based on the recommended total quantity of nutrients in continuous and pulse modes to the column. The soil parameters, initial and boundary conditions used in the model were obtained through experimental studies. The HYDRUS-2D model was developed, calibrated and validated with experimental results. The model performed could predict well the experimental data. Under continuous irrigation, nitrification (0.23/d) was the predominant process whereas both nitrification and denitrification occurs simultaneously in AWD with the overall nitrate removal efficiency of 60%. Consequently, the scenario prediction using this model for optimal fertigation schedule was done for groundnut crop. Further this model could be extended for various scenario predictions for designing optimal irrigation-fertigation schedules for sustainable agricultural practices.
Plant and Soil, 2006
Mathematical models may be used to develop management strategies that optimize the use of nutrients from complex sources such as manure in agriculture. The Precision Nitrogen Management (PNM) model is based on the LEACHN model and a maize N uptake/growth and yield model and focuses on developing more precise N management recommendations. The PNM model was evaluated for simulating drain flow nitrate-nitrogen (NO 3 -N) in a 3-yr study involving different times of liquid manure application on two soil textural extremes, a clay loam and a loamy sand under maize (Zea mays, L.) production. The model was calibrated for major N transformation rate constants including mineralization, nitrification and denitrification, and its performance was tested using two different calibration scenarios with increasing levels of generalization: (i) separate sets of rate constants for each individual soil type and (ii) a single set of rate constants for both soil types. When calibrated for each manure application treatment for each soil type, the model provided good simulations of monthly and seasonal drain flow NO 3 -N concentrations. The correlation coefficient (r) and Willmott's index of agreement (d) ranged from 0.63 to 0.96 and 0.72 to 0.92, respectively. The calibrated model performed reasonably well when rate constant values averaged over manure application treatment for each soil type were used, with r and d values between 0.54 and 0.97, and 0.70 and 0.94, respectively, and greater accuracy for the clay loam soil. When rate constant values were averaged over manure application treatments and soil types, model performance was reasonably accurate for the fall time manure application on the clay loam (r and d of 0.60 and 0.91 and 0.72 and 0.92, respectively) and satisfactory for the spring time on the clay loam and the fall and spring times for the loamy sand soil (r and d between 0.56 and 0.90 and 0.58 and 0.84, respectively). The use of the model for predicting N dynamics under manure-fertilized maize cropping appears promising.
@Bullet Modeling Water and Nitrogen Behavior in the Soil-Plant System
zone, a sink for nitrogen and water, and a means of measuring the response to environmental conditions. The flow diagram of the model is given in . The relations used are described in .detail and are as general as possible so that they SUMMARY A set of dynamic mathematical relations is developed for the major variables of soil water, nitrate, ammonium, available organic nitrogen, and plant growth and nitrogen uptake. Daily climatic conditions are used to control evapotranspiration and modify the rates of plant growth and soil processes. Inputs of irrigation water and fertilizer can be controlled to reduce leaching of nitrate.