Speaker
Description
Introduction
Cultivating cover crops is considered one of the most promising practices for agricultural soil carbon sequestration (Kaye and Quemada 2017). However, biophysical estimates of the potential for offsetting greenhouse gas emissions (GHG) by cover crops have been critiqued as unrealistic (Moinet et al., 2023). This is due to the omission of agronomic and socioeconomic constraints, such as the length of the growing season. Understanding and incorporating farmers’ views on the feasibility of soil carbon sequestration practices is an indispensable step before implementing any schemes for carbon sequestration in agricultural land.
We developed and tested a methodological framework to quantify the potential adoption of cover crops in three European countries (the Netherlands, Germany and Spain). Using this framework, we answered the following research questions: (1) What is the current adoption of cover crop cultivation? (2) What is the potential and adoption gap for the cultivation of cover crops? (3) Which agronomic constraints hinder further implementation?
Materials and Methods
Qualitative interviews were conducted with agricultural experts in each region (n = 8) to gain a deeper understanding of the farming systems and used to formulate a context-specific questionnaire distributed online at the three study sites.
We developed a framework that allowed the quantification of adoption gaps, identifying constraints that lie beyond the farmer’s immediate control or those that can be optimised through best management. Data was collected through an online survey among 321 farmers in three European countries (Germany, the Netherlands and Spain). Farmers were asked to report their crop rotation, cover crop cultivation and area of crops sown in spring. Based on these data, we quantified the potential agronomic adoption and relative adoption gap. Afterwards, farmers were asked to evaluate drivers and constraints linked to their adoption gap. Comparing adoption rates across different edaphic and environmental settings provided a context-specific overview of opportunities for increased adoption (figure).
Results
First results show that the current adoption of cover crops varies greatly depending on climate: While almost all farmers employed cover crops in the Netherlands, around 80% of the farmers did so in Germany and only 10% in Spain.
In Germany and the Netherlands, current adoption rates are close to the attainable potential, with further expansion limited due to existing winter cover in the crop rotation. On average, the adoption gaps were around 25% and 20% of the agricultural area in the Netherlands and Germany, respectively, when considering the share of land with a spring-sown crop. In Spain, adoption is constricted by water availability. Only a few farmers adopt cover crops in irrigated arable land.
Agronomic constraints generally impede the further expansion of cover crops. In the Netherlands and Germany, the most cited constraints were related to cover crop establishment, especially after a late harvest of a previous crop.
Discussion
Our findings show that, based on growing seasons, there is only a small gap for cover crop expansion in Germany and the Netherlands. Moreover, the continuous implementation of cover crops faces challenges from weather constraints, particularly following late harvests and, in Spain's case, water availability, which make the successful establishment of a cover crop in all fields and all seasons challenging.
Given the narrow-identified gaps and the fact that most of those gaps can be explained by agronomic constraints outside management optimisation, continuous adherence to the practice might not be feasible. Based on these insights, there is a limited agronomic potential for additional C sequestration by cover crops in Europe.
Despite multiple policies and regulations encouraging adoption, based on the agronomic constraints presented here, we estimate that some of the forecasted biophysical potentials of C sequestration are overestimated by at least 70% for our study sites, without considering other limiting factors, such as saturation or leakage effects.
References
Kaye, J.P., Quemada, M. Using cover crops to mitigate and adapt to climate change. A review. Agron. Sustain. Dev. 37, 4 (2017). https://doi.org/10.1007/s13593-016-0410-x
Moinet, G. Y., Amundson, R., Galdos, M. V., Grace, P. R., Haefele, S. M., Hijbeek, R., Van Groenigen, J.W.,, Van Groenigen, K.J., David S. & Powlson, D. S. (2023). Climate change mitigation through soil carbon sequestration in working lands: A reality check. Global Change Biology, 30(1), e17010.
| Keywords | soil carbon; cover crops; adoption; climate change mitigation; farmers survey |
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