Development and application of a solute transport model to describe field-scale nitrogen processes during autumn rains

Abstract

A new generic, three-dimensional, solute transport component was developed into FLUSH, which is a hydrological model developed for Nordic conditions. Water flow and solute transport descriptions in FLUSH follow the dual-permeability concept, which divides the total soil pore space into mobile soil matrix and macropore systems. The solute transport model was parameterized to simulate the main processes of nitrogen (N) cycle in clayey, subsurface-drained soils during autumn periods after the harvest. The model simulates transport of nitrate and ammonium N, as well as mineralization, nitrification, and denitrification. Reactions in soil are affected by temperature and moisture, as simulated by FLUSH. Ammonium can adsorb on soil particles in both pore systems, while organic N is described in simulations as an immobile solute in the soil matrix. One-dimensional version of the model was applied to two subdrained field sections (1.3 and 3.4 ha) in the Nummela experimental field in southern Finland during two autumn periods (2008 and 2011). The model was able to replicate the measured dynamics of nitrate N concentrations in drain discharge during both the periods. Concentrations were the most dependent on drain discharge dynamics and the rate of nitrification. Measured and simulated ammonium concentrations in drain discharge were about 10 times smaller than nitrate concentrations, even though the levels of N input with initial values and deposition for both inorganic fractions were similar. Successful solute transport simulation results further increase the confidence in the description of the water flow processes in FLUSH.

Keywords:

• FLUSH model
• solute transport
• nitrogen
• clay soil
• subsurface drains
• agriculture

Acknowledgments

We acknowledge CSC – IT Center for Science Ltd. for the allocation of computational resources. We would like to acknowledge Helena Äijö, Laura Alakukku, and Merja Myllys for their support in the research project. We thank Johannes Deelstra and anonymous reviewers for their constructive comments.

Additional information

Funding

This study was funded by Salaojituksen Tukisäätiö (the Finnish Drainage Foundation), the Ministry of Agriculture and Forestry, Maa- ja vesitekniikan tuki ry., and Sven Hallinin tutkimussäätiö (the Sven Hallin Research Foundation).