Long-term trends in corn yields and soil carbon under diversified crop rotations
Jarecki, M., Grant, B., Smith, W., Deen, B., Drury, C., VanderZaag, A., Qian, B., Yang, J., Wagner-Riddle, C. (2018). Long-term trends in corn yields and soil carbon under diversified crop rotations. Journal of Environmental Quality, [online] 47(4), 635-643. http://dx.doi.org/10.2134/jeq2017.08.0317
Plain language summary
Accurately accounting for water budgets within regional agro-ecosystems is becoming an
increasingly important practice as both climate change and water consumption pressures
have the potential for influencing agro-productivity and other water use activities. In this
study, water budget measurements from ten rain-fed experimental sites across Canada were
utilized to evaluate the performance of three models for their water partitioning capabilities:
DeNitrification DeComposition (DNDC), Holos, and Versatile Soil Moisture Budget (VSMB).
To assess the likely model performance at an up-scaled national level, the models were
applied at the site level with no water component-specific calibration. Evapotranspiration (ET)
was found to be the dominate component of the water budget at the prairie sites (89-149% of
precipitation) (i.e. in comparison to runoff, tile drainage and deep percolation), while both ET
(37-73% of precipitation) and drainage (19-61% of precipitation) represented most of the
water outflow budget at the sites in Eastern/Atlantic Canada. As DNDC integrates daily crop
growth dynamics with nitrogen, water and heat stresses, in contrast to VSMB and Holos
which only utilize a water budget model, it was not surprising to find that DNDC consistently
out-performed the other two models across all the statistical performance metrics considered
at daily resolution.
Agricultural practices such as including perennial alfalfa (Medicago sativa L.), winter wheat (Triticum aestivum L.), or red clover (Trifolium pratense L.) in corn (Zea mays L.) rotations can provide higher crop yields and increase soil organic C (SOC) over time. How well process-based biogeochemical models such as DeNitrification- DeComposition (DNDC) capture the beneficial effects of diversified cropping systems is unclear. To calibrate and validate DNDC for simulation of observed trends in corn yield and SOC, we used longterm trials: continuous corn (CC) and corn-oats (Avena sativa L.)- alfalfa-alfalfa (COAA) for Woodslee, ON, 1959 to 2015; and CC, corn- corn-soybean [Glycine max (L.) Merr.]-soybean (CCSS), corn-corn- soybean-winter wheat (CCSW), corn-corn-soybean-winter wheat + red clover (CCSW+Rc), and corn-corn-alfalfa-alfalfa (CCAA) for Elora, ON, 1981 to 2015. Yield and SOC under 21st century conditions were projected under future climate scenarios from 2016 to 2100. The DNDC model was calibrated to improve crop N stress and was revised to estimate changes in water availability as a function of soil properties. This improved yield estimates for diversified rotations at Elora (mean absolute prediction error [MAPE] decreased from 13.4-15.5 to 10.9-14.6%) with lower errors for the three most diverse rotations. Significant improvements in yield estimates were also simulated at Woodslee for COAA, with MAPE decreasing from 24.0 to 16.6%. Predicted and observed SOC were in agreement for simpler rotations (CC or CCSS) at both sites (53.8 and 53.3 Mg C ha-1 for Elora, 52.0 and 51.4 Mg C ha-1 for Woodslee). Predicted SOC increased due to rotation diversification and was close to observed values (58.4 and 59 Mg C ha-1 for Elora, 63 and 61.1 Mg C ha-1 for Woodslee). Under future climate scenarios the diversified rotations mitigated crop water stress resulting in trends of higher yields and SOC content in comparison to simpler rotations.