Soil organic carbon and nitrogen responses to occasional tillage in a continuous no-tillage system

No-tillage (NT) practice is increasingly adopted to improve soil health and sustainability. However, long-term NT may increase soil organic carbon (SOC) and nutrient stratification, soil acidification, compaction, and herbicide resistance in weeds. Targeted strategic disturbance of continuous no-tillage is occasionally practiced to overcome challenges of long-term no-tillage, yet limited information is available on their impacts on SOC and nitrogen (N) components. We evaluated the response of SOC and N fractions to different tillage practices after the imposition of one-time strategic minimum tillage operation (i.e., stubble mulch tillage: SMT) in a continuous NT system in semi-arid drylands. Tillage treatments included conventional tillage (CT), NT, SMT, and strip-tillage (ST). The CT, NT, and ST plots were established in 2013, and SMT plots were established with only one pass of stubble mulch tillage in september of 2019 in long-term NT plots. Soil samples were collected from 0 to 15 and 15–30 cm depth of each plot before SMT and 2-days, 7-months, 14-months, 19-months, and 26-months after SMT implementation. The CT management resulted in 12–27% and 11–16% lower SOC concentration than under NT, SMT, and ST in 0–15 and 15–30 cm depth, respectively. The CT and ST had 22–53%, 44–79%, and 43% greater soil inorganic N than NT and SMT after 2-days, 7-months, and 19-months, respectively, in 0–15 cm depth. The 3d-carbon dioxide-carbon (CO2-C) was 32–65%, 48–65%, 62–102%, and 122–195% greater under CT and ST than under NT and SMT after 2-days, 7-months, 19-months, and 26-months, respectively, in 0–15 cm depth. The microbial biomass carbon (MBC) showed varying responses, with 31–64% lower MBC after 2-days and 26-months, but it was 35–39% greater after 7-months under CT than under NT and SMT. There was no difference between NT and SMT systems on SOC and N fractions for most of the samplings. Further research may reveal how often SMT can be utilized in a long-term NT system without negative impacts on soil properties in semi-arid dryland cropping systems. This study showed one stubble mulch tillage after six years of continuous NT did not affect SOC and N concentrations in 0–30 cm depth.