Response of soil organic carbon fractions and microbial community composition to 33 years of tillage systems and organic amendments

One of the challenges for ensuring the resilience of agroecosystems is selecting agricultural practices that mitigate the effects of climate change and improve soil health. Extensive tillage has decreased the initial soil organic carbon (SOC) content. No-tillage (NT) can restore SOC by reducing soil disturbance and minimizing erosion. Organic amendments can provide faster SOC recovery and promote microbial activity. This study assessed the effect of tillage systems and organic amendments on SOC accumulation, SOC physical fractions, and the soil microbial community. A long-term study has been conducted for 33 years in Manhattan, KS, USA, comparing conventional tillage (CT) and NT. Plots with continuous corn were amended with mineral (MF) and organic fertilizer (OF) at a rate of 168 kg N ha^-1, in addition to a control treatment without fertilization (CO). Measurements included SOC stocks and physical fractions (POC - Particulate organic carbon >53 µm and MAOC - mineral-associated organic carbon <53 µm) at 0-5, 5-15, 15-30, and 30-45 cm, and soil microbial, fungi, and bacteria biomass at 0-5 cm. The use of OF increased microbial biomass, total fungi, and total bacteria. When comparing tillage and fertilizer combinations, SOC stock was higher under NT-OF than under all other tillage and fertilizer combinations. Additionally, OF increased POC stocks in both NT and CT at 0-5 and 5-15 cm. Organic fertilizer also increased the MAOC stocks in NT and CT at 0-5, 5-15, and 15-30 cm. Overall, we observed that NT enhanced the effect of OF on increasing SOC, POC, and MAOC stocks.