The role of cover crops for cropland soil carbon, nitrogen leaching, and agricultural yields – a global simulation study with LPJmL (V. 5.0-tillage-cc)

Abstract

Abstract. Land management practices can reduce the environmental impact of agricultural land use and production, improve productivity, and transform cropland into carbon sinks. In our study we assessed the biophysical and biogeochemical impacts and the potential contribution of cover crop practices to sustainable land use. We applied the process-based, global dynamic vegetation model LPJmL (Lund–Potsdam–Jena managed Land) V. 5.0-tillage-cc with a modified representation of cover crops to simulate the growth of grasses on cropland in periods between two consecutive main crops' growing seasons for near-past climate and land use conditions. We quantified simulated responses of agroecosystem components to cover crop cultivation in comparison to bare-soil fallowing practices on global cropland for a period of 50 years. For cover crops with tillage, we obtained annual global median soil carbon sequestration rates of 0.52 and 0.48 t C ha−1 yr−1 for the first and last decades of the entire simulation period, respectively. We found that cover crops with tillage reduced annual nitrogen leaching rates from cropland soils by medians of 39 % and 54 % but also the productivity of the following main crop by an average of 1.6 % and 2 % for the 2 analyzed decades. The largest reductions in productivity were found for rice and modestly lowered ones for maize and wheat, whereas the soybean yield revealed an almost homogenously positive response to cover crop practices replacing bare-soil fallow periods. The obtained simulation results of cover crop with tillage practices exhibit a good ability of the model version to reproduce observed effects reported in other studies. Further, the results suggest that having no tillage is a suitable complementary practice to cover crops, enhancing soil carbon sequestration and the reduction in nitrogen leaching, while reducing potential trade-offs with the main-crop productivity due to their impacts on soil nitrogen and water dynamics. The spatial heterogeneity of simulated impacts of cover crops on the variables assessed here was related to the time period since the introduction of the management practice as well as to environmental and agronomic conditions of the cropland. This study supports findings of other studies, highlighting the substantial potential contribution of cover crop practices to the sustainable development of arable production.

Estimating the Global Influence of Cover Crops on Ecosystem Service Indicators in Croplands With the LPJ‐GUESS Model

“…Moreover, including the no-till technique in cover cropping in our simulations had the potential to further mitigate N leaching (41% in CC L NT vs. 34% in CC L ; Table 2) mainly due to the reduced net N mineralization rates (Figure S7 in Supporting Information S1). This is in line with the findings from a meta-analysis by Thapa et al (2018) and a recent modeling study by Porwollik et al (2022).…”

“…Likewise, in some arid and semi‐arid regions, as well as temperature‐limited areas in the high latitudes (e.g., Canada) a slight decrease of N leaching in response to cover cropping systems was found, as poor growth conditions constrained the CC capacity for soil N uptake. In addition, the rapid turnover rate of SOM pools driven by warm and moist climate (Olin, Lindeskog, et al., 2015), together with abundant precipitation may increase N leaching with cover crop practices in the humid tropics (Figure 6) as a result of high biomass of N returned to soils (Figure S6 in Supporting Information S1) and enhanced throughflow (Porwollik et al., 2022).…”

“…Since large‐scale statistics on actual cover crop acreage do not exist, the CA area was used to represent the potential cover crop distribution on agricultural soils, following setups in a recent modeling study (Porwollik et al., 2022). We here performed all global simulations under three CA area scenarios: (a) CA his , representing the approximate area of CA practice currently adopted in global croplands; (b) CA pot , representing the potential agricultural lands that might implement CA systems under present socio‐economic and soil biophysical conditions; (c) CA all , assuming all cropland that was under CA management.…”

“…These models have been widely used to investigate soil C‐N dynamics and crop yields in response to CCs in different farming systems (e.g., APSIM, Chatterjee et al., 2020; DSSAT, Salmerón et al., 2014; DNDC, Singh & Kumar, 2022; ECOSYS, Qin et al., 2023). However, compared to site‐level modeling studies, an assessment of the impacts of CCs across regions or globally is still lacking, as a result of inadequate management information (e.g., spatial pattern of cover crop types) and missing or incomplete cover cropping representation in models (Porwollik et al., 2022). For large‐scale C‐N cycle modeling assessments, alternative agricultural practices so far have been evaluated through stylized model setups with homogenous assumptions of management intensities (Jang et al., 2021; Lutz et al., 2020; Ma, Rabin, et al., 2022; Olin, Lindeskog, et al., 2015).…”

Current NPP cannot predict future soil organic carbon sequestration potential. Comment on “Photosynthetic limits on carbon sequestration in croplands”

“…Global analysis of soil C sequestration potential should be based on a well-calibrated model on gridded NPP, proper climate and soil data, and accounting for all sources of uncertainties. For example, a recent global modelling study on the potential of cover cropping found the median global soil carbon sequestration rates of 0.48 and 0.52 t C ha − 1 yr − 1 (Porwollik et al, 2022).…”