The Carbon Budget of Agroecosystems in Relatin to Tillage and Nitrogen Fertilizer Management

Abstract

Soil organic carbon (SOC) is a crucial component of soil fertility and functionality. Agricultural intensification, particularly tillage and heavy nitrogen (N) fertilization, has led to SOC depletion in croplands, ultimately contributing to increased atmospheric CO₂ concentration. Adoption of no-till (NT) and balanced N management can boost plant productivity, increase crop residue input and improve soil structure, ultimately enhancing SOC storage and mitigating climate change. However, in some contexts, these benefits do not materialize due to concurrent increase in greenhouse gas (GHG) emissions, especially nitrous oxide (N2O), which can offset SOC gains. Few studies have systematically investigated the interactive effects of NT and N fertilization on SOC accumulation, SOC characteristics and GHG emission; thus, an important knowledge gap exists regarding the net impact of these agronomic interventions on the carbon (C) budget of agroecosystems. To address this gap, a comprehensive field and laboratory study was conducted using experimental plots (established in 1970 at the University of Kentucky) under continuous corn, managed with either moldboard plow (MB) or no-tillage (NT), and receiving N fertilizer at rates of 0, 84 and 168 kg N ha-1 y-1. Using soil ¹³C abundance and an isotope‐mixing model, corn-derived SOC sequestration was quantified and partitioned into labile particulate organic matter (POM-C) and stable mineral-associated organic matter (MAOM-C). Several thermal oxidation techniques, including differential scanning calorimetry and thermogravimetry, were used to assess SOC stability. Field-measured GHG fluxes were converted into CO₂-C equivalents and subtracted from the SOC sequestration rate to calculate the net C budget. Compared to MB, NT increased SOC stocks, retained more corn-derived C, and lowered GHG emissions, yielding a net C balance of 0.17-0.47 Mg C ha-1 y-1 (versus ~0.07 under MB). Data on MAOM formation and thermal oxidation also showed greater SOC stability under NT. These results underscore that NT, with a balanced N fertilization regime, is an effective strategy to enhance soil health and minimize the carbon footprint of agroecosystems.