Long‐term zero‐tillage enhances the protection of soil carbon in tropical agriculture

Abstract

Contrasting tillage strategies not only affect the stability and formation of soil aggregates but also modify the concentration and thermostability of soil organic matter associated with soil aggregates. Understanding the thermostability and carbon retention ability of aggregates under different tillage systems is essential to ascertain potential terrestrial carbon storage. We characterized the concentration and thermostability of soil organic carbon (SOC) within various aggregate size classes under both zero and conventional tillage using novel Rock-Eval pyrolysis. The nature of the pore systems was visualized and quantified by X-ray computed tomography to link soil structure to organic carbon preservation and thermostability. Soil samples were collected from experimental fields in Botucatu, Brazil, which had been under zero-tillage for 2, 15 and 31 years, and from adjacent fields under conventional tillage. Soils under zerotillage significantly increased pore connectivity whilst simultaneously decreasing interaggregate porosity, providing a potential physical mechanism for protection of SOC in the 0-20-cm soil layer. Changes in the soil physical characteristics associated with the adoption of zero-tillage resulted in improved aggregate formation compared to conventionally tilled soils, especially when implemented for at least 15 years. In addition, we identified a chemical change in composition of organic carbon to a more recalcitrant fraction following conversion to zero-tillage, suggesting aggregates were accumulating rather than mineralizing SOC. These data reveal profound effects of different tillage systems upon soil structural modification, with important implications for the potential of zero-tillage to increase carbon sequestration compared to conventional tillage.

Soil organic matter fractions in an Oxisol under tillage systems and winter cover crops for 26 years in the Brazilian subtropics

“…So, in NT soil there is a mutual relationship between organic matter and aggregates which is important for soil structuring and soil C stabilization. That was also observed in the greater amount of macroaggregates and C stock for NT (Table 2), agreeing with the studies of Tivet et al (2013, Wuaden et al (2020) and Cooper et al (2021) in Brazilian soils.…”

Zero tillage has important consequences for soil pore architecture and hydraulic transport: A review

“…Ploughing can also temporarily alleviate compaction stress from intensive or poorly timed traffic, although it is well established that regular tillage leads to degradation of important biophysical properties, resilience and the ecology of the soil (Lal et al, 2007). As such, CT has been implicated in reducing biomass or abundance of soil macrofauna, mesofauna, and microorganisms (Kladivko, 2001;Briones and Schmidt, 2017), in increasing susceptibility to compaction and erosion (Hamza and Anderson, 2005;Blanco-Canqui and Ruis, 2018;Klik and Rosner, 2020), and increasing greenhouse gases emissions from soil, especially CO 2 (Cooper et al, 2021a). Conversely, no-or zero-tillage (ZT) and minimum or reduced tillage are key strategies associated with Conservation Agriculture (CA) (Gonzalez-Sanchez et al, 2017).…”

Detection and Quantification of Low Levels of Carbonate Mineral Species Using Thermogravimetric-Mass Spectrometry to Validate Co2 Drawdown Via Enhanced Rock Weathering

“…The technique was commonly used for soil and sediment analysis but has now largely been replaced by the more detailed Rock-Eval pyrolysis (e.g. Pillot et al, 2014;Cooper et al, 2021). During Rock-Eval pyrolysis, samples are heated to 300 • C for 3 min, then ramped to 650 • C at a rate of 25 • C min − 1 in an inert N 2 atmosphere.…”