The effect of crop establishment system on soil heterotrophic respiration pre- and post-establishment: initial results.

Soil heterotrophic respiration is the process by which carbon stored in soil is released into the atmosphere as CO₂ through microbial breakdown of organic matter. This process influences the balance between carbon storage and release, impacting soil carbon levels. Factors such as soil temperature, soil moisture, and the availability of organic material determine CO₂ emissions. Tillage practices alter this soil respiration process by changing soil structure, impacting on airflow, and microbial activity, which influence decomposition rates and CO₂ fluxes. Understanding these interactions is critical for sustainable farming and reducing greenhouse gas emissions from soils. This study explored the effects of different wheat establishment systems: plough (P), minimum tillage (MT), and direct drilling (DD), on the heterotrophic respiration in a long-term plot-scale experiment at Teagasc Oak Park, Ireland. Treatments were replicated four times in a randomized block design on a site where P and MT treatments were in place since 2001, with DD practiced since 2021. Measurements were taken in situ using closed chambers and a portable FTIR gas analyser (Gasmet GT5000 Terra) from September 2024 to the end of December 2024, with plans for continued monitoring beyond this timeframe. For analysis, the experimental timeline was divided into two phases: Period 1 (P1), starting from the 9th of September (following the MT event) and ending on the 10th of October (the ploughing day), and Period 2 (P2), continuing from this point to the last measurement taken in December 2024. Results demonstrated that tillage treatments significantly influenced soil respiration. During P1, MT consistently displayed higher daily CO₂ emissions due to soil disturbance and incorporation of crop residues, DD and P did not differ significantly from each other. With lower temperatures in P2, MT sustained a significant greater flux compared to the other treatments, supported by its great soil moisture retention and moderate sensitivity to temperature variations (r = 0.569).  While ploughing at the start of P2 P resulted in a temporary spike in CO₂ fluxes on the P plots, this diminished rapidly. With emissions strongly influenced by temperature variations (r = 0.603), this decline was further driven by a significant drop in air temperature and P's limited soil moisture retention, which may have suppressed microbial activity. This resulted in lower overall soil respiration fluxes from P compared to MT but not significantly different from those of DD in the reported time frame. Cumulative fluxes further emphasized these differences: MT recorded the highest emissions (577.39 kg CO₂-C ha⁻¹), followed by P (470.89 kg CO₂-C ha⁻¹) and DD (394.74 kg CO₂-C ha⁻¹). These findings highlight the varying impacts of tillage practices on soil carbon dynamics driven by an interaction with environmental factors such as soil moisture and temperature.

Keywords: Soil heterotrophic respiration, Tillage practices, Carbon dynamics, Greenhouse gas emissions