Deep ploughing increases agricultural soil organic matter stocks

Abstract

Subsoils play an important role within the global C cycle, since they have high soil organic carbon (SOC) storage capacity due to generally low SOC concentrations. However, measures for enhancing SOC storage commonly focus on topsoils. This study assessed the long-term storage and stability of SOC in topsoils buried in arable subsoils by deep ploughing, a globally applied method for breaking up hard pans and improving soil structure to optimize crop growing conditions. One effect of deep ploughing is translocation of SOC formed near the surface into the subsoil, with concomitant mixing of SOC-poor subsoil material into the 'new' topsoil. Deep-ploughed croplands represent unique long-term in situ incubations of SOC-rich material in subsoils. In this study, we sampled five loamy and five sandy soils that were ploughed to 55-90 cm depth 35-50 years ago. Adjacent, similarly managed but conventionally ploughed subplots were sampled as reference. The deep-ploughed soils contained on average 42 ± 13% more SOC than the reference subplots. On average, 45 years after deep ploughing, the 'new' topsoil still contained 15% less SOC than the reference topsoil, indicating long-term SOC accumulation potential in the topsoil. In vitro incubation experiments on the buried sandy soils revealed 63 ± 6% lower potential SOC mineralisation rates and also 67 ± 2% lower SOC mineralisation per unit SOC in the buried topsoils than in the reference topsoils. Wider C/N ratio in the buried sandy topsoils than in the reference topsoils indicates that deep ploughing preserved SOC. The SOC mineralisation per unit SOC in the buried loamy topsoils was not significantly different from that in the reference topsoils. However, 56 ± 4% of the initial SOC was preserved in the buried topsoils. It can be concluded that deep ploughing contributes to SOC sequestration by enlarging the storage space for SOC-rich material.

Pressures on soil functions from soil management in Germany. A foresight review

“…Especially in terms of C sequestration, the subsoil is understood to be a long-term sink because of the physical protection of the overlying topsoil. Differences in the subsoil texture compared to the topsoil may as well affect the carbon sequestration potential (Alcantara et al 2016). The research fits well with current policies of the UNFCCC's Paris Agreement (Paris Agreement 2015) and the "4 per 1000" initiative (Ministère de l'Agriculture 2015/2016), of which Germany is part.…”

“…Research is a key driver here because potential new measures of and additional arguments for subsoil management seem to be primarily discussed within the scientific community. Therein, subsoil management is discussed in terms of sequestering carbon (climate change mitigation) (Kell 2012;Alcantara et al 2016;Lorenz and Lal 2005), water conserving tillage (climate change adaptation) (Sang et al 2016), and phosphorous efficiency (resource scarcity) (Ekelöf et al 2015;Zhang et al 2016). Thus, research is now providing more arguments for subsoil management in relation to current societal challenges, thereby potentially creating a meaningful impact.…”

“…This factor must affect plant protection strategies, Research on measures to improve soil biodiversity affecting resilience against pathogens and reducing the need for pesticides; precise application (see 5.1) reduces amounts used Increasing research, including monitoring improvements in Europe, to show the positive effects of different organic inputs on soil biodiversity (soil threats) and climate change mitigation and adaptation Stone et al 2016;Alcantara et al 2016;FAO 2016b;Diacono and Montemurro 2010;Larkin 2015;Thies et al 2015;Smith et al 2013;Berndes et al 2015;Griffiths et al 2016 in connection with 4.3.3…”

“…In addition, by increasing SOC, organic inputs are strongly linked to climate change mitigation and adaptation, e.g., by putting organic matter into the subsoil (Alcantara et al 2016).…”

The ‘Invisible’ Subsoil: An Exploratory View of Societal Acceptance of Subsoil Management in Germany

“…In this context, researchers have begun to look more systematically at subsoil functions/the role of subsoil for soil functions and to develop and investigate new strategies of mechanically or biologically intervening in subsoils that aim to tap the subsoil as a resource [10][11][12][13][16][17][18]]. Yet how relevant, feasible, and acceptable are different methods for subsoil management as a strategy that can contribute to the sustainable management of soils and to securing long-term agricultural yields?…”