Modeling Flood-Induced Stress in Soybeans

Abstract

Despite the detrimental impact that excess moisture can have on soybean (Glycine max [L.] Merr) yields, most of today's crop models do not capture soybean's dynamic responses to waterlogged conditions. In light of this, we synthesized literature data and used the APSIM software to enhance the modeling capacity to simulate plant growth, development, and N fixation response to flooding. Literature data included greenhouse and field experiments from across the U.S. that investigated the impact of flood timing and duration on soybean. Five datasets were used for model parameterization of new functions and three datasets were used for testing. Improvements in prediction accuracy were quantified by comparing model performance before and after the implementation of new stage-dependent excess water functions for phenology, photosynthesis and N-fixation. The relative root mean square error (RRMSE) for yield predictions improved by 26% and the RRMSE predictions of biomass improved by 40%. Extensive model testing found that the improved model accurately simulates plant responses to flooding including how these responses change with flood timing and duration. When used to project soybean response to future climate scenarios, the model showed that intense rain events had a greater negative effect on yield than a 25% increase in rainfall distributed over 1 or 3 month(s). These developments advance our ability to understand, predict and, thereby, mitigate yield loss as increases in climatic volatility lead to more frequent and intense flooding events in the future.

Keywords: APSIM; climate change; excess water; flooding; modeling; soybean.

Figure 1

Moisture stress factors in the APSIM soybean model. (A) drought stress factors already present in APSIM. (B) Excessive moisture stress factors for photosynthesis, phenology, and fixation added and tested in this study with the exception of root growth which was already part of APSIM 7.9.

Figure 2

Model evaluation for yield (A, B) and biomass (C, D) data in both flooding duration (solid blue line) and timing (dashed blue line) studies relative to a 1:1 reference line (dotted black line). Relative root mean square error (RRMSE), modeling efficiency (ME) and R² for each dataset are included in the panel.

Figure 3

In-season simulation of biomass accumulation under different flooding treatments in experiments 1 (A), 2 (B), and 3 (C) (all located in Arkansas, experiments 1 and 3 on Sharkey Clay soil and experiment 2 on Crowley Silt Loam soil; see Table 1 for more details). Lines represent APSIM model simulations, and points, the measured data from the experiments.

Figure 4

Simulated grain yield and biomass with the improved and original APSIM model (lines) versus experimental data (filled cycles) from flooding duration (left panels) and flooding timing (right panel) studies. The flooding events for the duration studies (A–D) were initiated at V4 (4^th leaf) and R2 (early reproductive stage). The flooding events for the timing studies (E–H) were initiated at V4 (4^th leaf), R1 (Beginning of reproductive phase), R3 (beginning of pod filling period), and R5 (end of pod filling period).

Figure 5

Testing of the improved model (lines) against two independent datasets (points). Left panels show model evaluation for yield (A, C, E) and right panels model evaluation for in-season biomass accumulation (B, D, F). See Table 1 for experimental details.

Figure 6

Sensitivity analysis of oxdef_photo parameters on a silt loam soil (A) and clay soil (B). The output variables (y-axis) shown in each graph are biomass (kg ha-1), N uptake (kg ha-1), N fixation (kg ha-1), maximum root depth (cm), and end of season grain yield (kg ha-1). In the legends, the numbers in parentheses in the output variables refer to the default values.

Figure 7

APSIM soybean simulations of soybean % yield penalty in different soils panel (A), 30-year weather (1988-2018) plus 25% increased precipitation amount on soybean yields panel (B), and 30-year weather plus extreme rain evens on soybean yields panel (C). Soil texture for each experiment is provided in panel C, further details are provided in Table 1.