Location: Watershed Management ResearchTitle: Improving SHAW long-term soil moisture prediction for continuous wheat rotations, Alberta, Canada) Author
Submitted to: Canadian Journal of Soil Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/24/2009
Publication Date: 4/15/2010
Publication URL: parking.nal.usda.gov/shortterm/21525_Hong_-2010-CJSS90.37-53.pdf
Citation: Wang, H., Flerchinger, G.N., Lemke, R., Brandt, K., Goddard, T., Sprout, C. 2010. Improving SHAW Long-Term Soil Moisture Prediction for Continuous Wheat Rotations, Alberta, Canada. Canadian Journal of Soil Science, 90:37-53. Interpretive Summary: The DSSAT-CSM model is a widely-used crop growth model, but its simulations of soil moisture and temperature are not always satisfactory. The SHAW model is a widely-used model that can accurately simulate soil water and temperature, but cannot simulate crop growth. The feasibility of coupling these two models was investigated by using wheat growth information simulated by the DSSAT-CSM to drive soil moisture simulations of the SHAW model. Soil moisture simulated by the SHAW model using crop growth information from the DSSAT-CSM model were significantly better than those using the DSSAT-CSM model alone. Results indicate that a full coupling of the two models should be implemented to improve simulation of crop growth, yield, nitrogen leaching, etc. provided by the DSSAT-CSM model, thereby making it a more reliable model for land managers.
Technical Abstract: The Decision Support System for Agrotechnology Transfer-Cropping System Model (DSSAT-CSM) is a widely used modeling package that often simulates wheat yield and biomass well. However, some previous studies reported that its simulation on soil moisture was not always satisfactory. On the other hand, the Simultaneous Heat and Water (SHAW) model, a more sophisticated, hourly time step soil microclimate model, needs inputs of plant canopy development over time, which are difficult to measure in the field especially for a long-term period (longer than a year). The SHAW model also needs information on surface residue, but treats them as constants. In reality, however, surface residue changes continuously under the effect of tillage, rotation and environment. We therefore proposed to use DSSAT-CSM to simulate dynamics of plant growth and soil surface residue for input into SHAW, so as to predict soil water dynamics. This approach was tested using three conventionally-tilled wheat rotations (continuous wheat, wheat-fallow and wheat-wheat-fallow) of a long-term cropping systems study located on a Thin Black Chernozemic clay loam near Three Hills, Alberta, Canada. Results showed that DSSAT-CSM often overestimated the drying of the surface layers in wheat rotations, but consistently overestimated soil moisture in the deep soil. This is likely due to the underestimation of root water extraction despite model predictions that the root system reached 80 cm. Among the eight growth/residue parameters simulated by DSSAT-CSM, root depth, leaf area index and residue thickness are the most influential characteristics on the simulation of soil moisture by SHAW. The SHAW model using DSSAT-CSM-simulated information significantly improved prediction of soil moisture at different depths and total soil water at 0-120 cm in all rotations with different phases compared with that simulated by DSSAT-CSM.