Long-term model simulation of yield and GHG emissions: Sustaining dryland winter wheat systems with one-time composted cattle manure application and annual cover cropping

Dryland winter wheat-fallow rotation in the US Northern High Plains face soil fertility and climate-related challenges, which contribute to low yields and reduced sustainability. Greenhouse gas (GHG) emissions and wheat yield were monitored following a one-time compost (0, 15, 30, and 45 Mg ha⁻¹) in 20015 combined with annual cover cropping (2:1 Austrian winter pea and oats) during fallow phases. This study used the DAYCENT biogeochemical model to assess climate-smartness of the management, and determine the optimal timing for compost re-application between 2015 to 2050. The model was validated using field GHG observations and wheat yields from 2016, 2017 and 2018. The model showed positive correlations between observed and simulated carbon dioxide (CO₂, R² = 0.62), methane (CH₄, R² = 0.64), nitrous oxide (N₂O, R² = 0.52) emissions, and grain yield (R² = 0.93). Simulations for the period between 2015 to 2050 revealed that CO₂ and N₂O emissions peaked at 923 mg C m ^-2 hr ^-1 and 78 µg N m ^-2 hr ^-1 around 7 years after one-time compost application; and remained elevated between 923 to 1030 mg C m ^-2 hr ^-1 and 57 to 78 µg N m ^-2 hr ^-1 until 2031 and 2033 respectively, before gradually declining. CH₄ was consistently assimilated throughout the simulation, with an average of 99% greater uptake in compost and annual cover-crop- amended soils. Wheat yield followed a similar trajectory, declining slightly during the first 3-5 years, then increasing until year 15 (2031), after which yields gradually declined across all treatments. The simulations suggest that a single 45 Mg ha ^-1 compost application integrated with annual cover cropping can enhance soil function, increase productivity, and maintain a favorable GHG profile for 10 – 15 years (up to 2030). Compost re-application is necessary beyond this period to sustain long-term agronomic and environmental benefits.