Soil organic carbon dynamics in semi-arid irrigated cropping systems

Authors: Bierer, Andrew; Leytem, April; Dungan, Robert - Rob; MOORE, AMBER - Oregon State University; Bjorneberg, David - Dave

Submitted to: Agronomy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/25/2021
Publication Date: 3/15/2021
Citation: Bierer, A.M., Leytem, A.B., Dungan, R.S., Moore, A., Bjorneberg, D.L. 2021. Soil organic carbon dynamics in semi-arid irrigated cropping systems. Agronomy. 11(484):1-30. https://doi.org/10.3390/agronomy11030484.
DOI: https://doi.org/10.3390/agronomy11030484

Interpretive Summary: Increasing organic carbon stored within the soil, soil organic carbon (SOC), is reported as a mitigation strategy for combating global climate change by the Intergovernmental Panel on Climate Change. Uncertainty in estimating the potential for SOC storage remains a current issue. This study aimed to identify the potential for SOC storage in three cropping systems in semi-arid irrigated croplands of Southern Idaho. A computer model using our experimental data was also used to predict SOC storage potential by 2050 under present day management conditions of the three cropping systems. Findings indicate that some cropping systems have the potential to store more SOC than others and that using dairy cattle manure as a fertilizer source can quickly increase SOC. When compared with regional soils records, the computer model may be overestimating the potential to store SOC in cropping systems using large quantities of manure. This study increases knowledge of SOC storage potential in semi-arid irrigated regions and could assist with improving computer models of SOC.

Technical Abstract: The insufficient characterization of soil organic carbon (SOC) dynamics in semi-arid climates contributes uncertainty to SOC sequestration estimates. The opportunity exists to improve estimates of SOC dynamics in irrigated semi-arid croplands by studying research locations in south-central Idaho. This study intended to estimate changes in SOC (0-30 cm depth) due to variations in manure management, tillage regime, adoption of winter cover, and crop rotation. Empirical data from three research locations was also used to drive denitrification decomposition (DNDC) models in a “default” and calibrated capacity as well as forecast SOC levels until 2050 under “high” and “low” emissions future climate scenarios. Empirical data indicates: (i) increasing C input results in more rapid increases in SOC; (ii) no effect (P = 0.51) of winter triticale on SOC after 3 years; (iii) SOC accumulation (0.6 ± 0.5 Mg ha-1 yr-1) under a dairy forage rotation of corn-barley-alfalfax3 and no change (P = 0.905) in a commercial rotation of wheat-potato-barley-sugarbeet; (iv) manure applied annually at rate 1X is not significantly different (P = 0.75) from biennial application at rate 2X; and (v) no significant effect of manure application timing (P = 0.41, fall vs spring). The DNDC model simulated empirical SOC and biomass C measurements adequately in a default capacity, yet specific issues were encountered. The calibration improved model fit however simulation of soil water contents and actual evapotranspiration remained unacceptable. By 2050, model forecasting suggested: (i) SOC stock was ~ 1 % different between future emissions scenarios; (ii) triticale cover resulted in SOC accrual (0.5 – 0.27 Mg ha-1 yr-1); (iii) when manure is applied, conventional tillage regimes are favored; and (iv) manure applied treatments accrue SOC fitting a quadratic relationship (all R2 > 0.85 and all P < 0.0001), yet extending the simulation to 2100 indicated no equilibrium was realized. It is possible that under very large C inputs that C sequestration is inaccurately favored by DNDC which may influence “NetZero” C initiatives. Our findings improve upon knowledge of SOC dynamics in semi-arid irrigated cropping systems and could aid DNDC model development endeavors.