Simulating the effect of tillage practices with the global ecosystem model LPJmL (version 5.0-tillage)

Abstract

Abstract. The effects of tillage on soil properties, crop productivity, and global greenhouse gas emissions have been discussed in the last decades. Global ecosystem models have limited capacity to simulate the various effects of tillage. With respect to the decomposition of soil organic matter, they either assume a constant increase due to tillage or they ignore the effects of tillage. Hence, they do not allow for analysing the effects of tillage and cannot evaluate, for example, reduced tillage or no tillage (referred to here as “no-till”) practises as mitigation practices for climate change. In this paper, we describe the implementation of tillage-related practices in the global ecosystem model LPJmL. The extended model is evaluated against reported differences between tillage and no-till management on several soil properties. To this end, simulation results are compared with published meta-analyses on tillage effects. In general, the model is able to reproduce observed tillage effects on global, as well as regional, patterns of carbon and water fluxes. However, modelled N fluxes deviate from the literature values and need further study. The addition of the tillage module to LPJmL5 opens up opportunities to assess the impact of agricultural soil management practices under different scenarios with implications for agricultural productivity, carbon sequestration, greenhouse gas emissions, and other environmental indicators.

The importance of management information and soil moisture representation for simulating tillage effects on N<sub>2</sub>O emissions in LPJmL5.0-tillage

“…In Lutz et al (2019a), model results deviated from meta-analyses when comparing simulated tillage effects on N 2 O emissions.…”

“…A full overview of the tillage implementation into LPJmL5.0 as well as affected soil properties and processes can be found in Lutz et al (2019a), the nitrogen implementation is described by Von Bloh et al (2018) and a comprehensive description of the LPJmL model is provided by Schaphoff et al (2018) and Schlüter et al (2018).…”

“…Rather than changing well-established functions on litter decomposition (Schlüter et al, 2018), we modified the parameter on bioturbation that was introduced by Lutz et al (2019a) and tested its effects on the reduction of the residue cover of the soil. Lutz et al (2019a) used an average value of 0.006 (m 2 g −1 ) (falsely described as 0.004 in their publication, but used so in the code: https://doi.org/10.5281/zenodo.2652136) to translate litter biomass into a fraction of soil being covered with residues, which was applied to all litter, neglecting variations in surface litter for different materials. The bioturbation rate was increased from 0.19% day −1 to 0.63% day −1 to account for the surface litter being transferred to the incorporated litter pool per day (equivalent to an annual bioturbation rate of 90%, versus 50% as assumed previously).…”

“…Lutz et al (2019a) found that LPJml overestimates N 2 O emissions. Because of the importance of soil moisture for N 2 O emissions, we tested if modifying the simulation of soil moisture can contribute to improving the simulation of N 2 O emission.…”

“…These processes are driven by microbial activity and strongly respond to soil properties such as moisture, temperature, oxygen, mineral N, and organic carbon (Mosquera et al, 2005;Snyder et al, 2009;Van Kessel et al, 2013). These soil properties are affected by tillage (Lutz et al, 2019a, c) and other management practices (e.g., fertilizer application and residue treatment) (Van Kessel et al, 2013).…”