Project topics and materials
Get Complete Project Material File(s) Now! »
DEVELOPMENT OF A LOCAL SCALE NITROGEN AND PHOSPHORUS CROP MODEL
The Soil Water Balance (SWB) model is a mechanistic, generic crop model originally developed for real-time irrigation scheduling (Annandale et al., 1999a). This model is based on a simple cascading soil water balance approach (Campbell and Diaz, 1988) although a 2-D finite difference model was also subsequently developed. A daily crop dry matter increment is calculated as being either water supply (Tanner and Sinclair, 1983) or solar radiation (Monteith, 1977) limited. Additionally, crop growth and water use can be simulated using the simpler FAO crop factor approach (Annandale et al., 1999b).
Since development, the model has undergone extensive testing for a wide range of different cropping systems (Jovanovic et al., 1999; Jovanovic and Annandale, 2000; Steyn, 1997; Jovanovic et al., 2002; Annandale et al., 2003; Tesfamariam 2004). The chemical equilibrium routine of Robbins (1991) and a weather generator were later included into SWB to investigate the long-term sustainability of irrigating crops with gypsiferous mine water (Annandale et al., 2002; Beletse, 2008).
Currently there are two forms of the model, the simpler version that can be easily used for applications such as irrigation scheduling, water use estimates and yield predictions referred to as SWB, and the more complex research version called SWB-Sci, which now contains salt and nutrient simulation capabilities, and is the focus of this chapter.
Chapter 1: Introduction
1.1 Rationale
1.2 Nitrogen leaching from cropping systems
1.3 Phosphorus leaching from cropping systems
1.4 Mitigation measures
1.4.1 Reducing N leaching in cropping systems
1.4.2 Reducing P leaching in cropping systems
1.5 Modelling N and P dynamics in agro-ecosystems
1.5.1 Overview
1.5.2 Background to SWB-Sc
1.6 Thesis objectives
1.6.1 Model development
1.6.2 Model testing
1.6.3 Model application
1.7 References
Chapter 2: Development of a local scale nitrogen and phosphorus crop model
2.1 Introduction
2.1 Source models from which algorithms were obtained
2.2 Model description
2.3 Conclusions
2.4 Acknowledgements
2.5 References
Chapter 3: Obtaining the parameters required to model labile phosphorus for South African soils
3.1 Introduction
3.2 Review of inorganic P modelling approach
3.3 Calcareous, slightly weathered and highly weathered soils
3.4 Estimation of inorganic P pool sizes
3.5 Obtaining inputs at catchment scale
3.6 General discussion
3.7 Conclusions
3.8 Acknowledgements
3.9 References
Chapter 4: Assessment of the ability of SWB-Sci to simulate nitrogen dynamics in agronomic cropping systems
4.1 Introduction
4.2 Materials and methods
4.3 Results
4.4 General discussion
4.5 Conclusions
4.6 Acknowledgements
4.7 References
Chapter 5: Modelling the effects of nitrogen and phosphorus stress on crop growth using SWB-Sci: An example using maize
5.1 Introduction
5.2 Materials and methods…
5.3 Results
5.4 General discussion
5.5 Conclusions
5.6 Acknowledgements
5.7 References
Chapter 6: Monitoring and modelling soil water nitrogen and phosphorus concentrations to estimate leaching losses
Chapter 7: Analysis of nitrogen and phosphorus leaching from dryland and irrigated cropping systems using long-term modelling
Chapter 8: Conclusions and recommendations
