Greenhouse gas emissions during decomposition of cover crops and poultry litter with simulated tillage in 90-day soil incubations

Investigating the impact of cover crops and manure on soil greenhouse gas (GHG) emissions is crucial for advancing our understanding of the climate-smart potential of organic management practices. This soil incubation experiment was conducted to investigate the combined effects of manure and cover crop residue decomposition on soil carbon dioxide (CO₂), nitrous oxide (N₂O), and methane (CH₄) emissions under simulated tillage conditions. Undisturbed soil cores, collected from an organic cotton (Gossypium hirsutum L.) field experiment, were incubated for 90 days in a 2 × 4 factorial design for 2 consecutive years. Four combinations of cover crop and poultry litter (PL) residues were the primary treatment factor. The amount of residues added in the incubation study reflected the cover crop biomass produced under field conditions and the amount of PL applied in the field. Residue treatments included PL only at the full application rate (250 kg ha⁻¹), PL with oat (Avena sativa L.), PL with turnip (Brassica rapa subsp. rapa), and half the rate of PL with Austrian winter pea (Pisum sativum) (AWP). The residues were either soil incorporated or surface applied to simulate disking and no-till field conditions. On average, 3.5% of applied carbon escaped as CO₂ during the 90-day incubation period across treatments. Similarly, on average, 0.75% of applied nitrogen escaped as N₂O. The proportion of nitrogen emitted as N₂O under simulated no-till was 81.2% higher in 2020 (P < 0.05) compared to conventional tillage. In 2021, N₂O emission was 35.8% higher (P < 0.1). When normalized over the amount of carbon added, total CO₂ equivalent GHG emissions were the highest in the legume AWP treatment for both years. However, neither residue types nor simulated tillage affected net soil CH₄ uptake (P > 0.1). While no-till practices may increase soil total carbon and nitrogen stocks during the cover crops and manure decomposition, the impact on GHG emissions depends on residue type and should be considered in estimating the climate-smart potential of organic management practices.