Soil Organic Carbon Dynamics in Semi-Arid Irrigated Cropping Systems

Insufficient characterization of soil organic carbon (SOC) dynamics in semi-arid climates contributes uncertainty to SOC sequestration estimates. This study estimated changes in SOC (0-30 cm depth) due to variations in manure management, tillage regime, winter cover crop, and crop rotation in southern Idaho (USA). Empirical data were used to drive the Denitrification Decomposition (DNDC) model in a default and calibrated capacity and forecast SOC levels until 2050. Empirical data indicates: (i) no effect (p = 0.51) of winter triticale on SOC after 3 years; (ii) SOC accumulation (0.6 +/- 0.5 Mg ha(-1) year(-1)) under a rotation of corn-barley-alfalfax3 and no change (p = 0.905) in a rotation of wheat-potato-barley-sugarbeet; (iii) manure applied annually at rate 1X is not significantly different (p = 0.75) from biennial application at rate 2X; and (iv) 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. By 2050, model forecasting suggested: (i) triticale cover resulted in SOC accrual (0.05-0.27 Mg ha(-1) year (ii) when manure is applied, conventional tillage regimes are favored; and (iii) manure applied treatments accrue SOC suggesting a quadratic relationship (all R-2 > 0.85 and all p < 0.0001), yet saturation behavior was not realized when extending the simulation to 2100. It is possible that under very large C inputs that C sequestration is favored by DNDC which may influence NetZero C initiatives.

Automated summary

Insufficient characterization of soil organic carbon dynamics in semi-arid climates contributes uncertainty to estimates of soil organic carbon sequestration. This study estimated changes in soil organic carbon due to variations in manure management, tillage regime, winter cover crop, and crop rotation in southern Idaho, USA. The DNDC model adequately simulated empirical soil organic carbon and biomass carbon measurements, but encountered specific issues when extended to a longer simulation period. By 2050, model forecasts suggested triticale cover crop resulted in soil organic carbon accrual, with a quadratic relationship observed in the effects of manure application on soil organic carbon.