A method for assessing and implementing sustainable crop production is needed to give practical relevance to the frequently used term “sustainable agriculture”. The objective of this paper is to present such a theoretical procedure. Therefore the terms “sustainability” and “sustainable crop production” are discussed and defined. On the basis of the definitions, an eight‐step procedure for assessing and implementing sustainable crop production is outlined. The steps are (1) identify emissions and other releases linked to different crop production practices, (2) trace each different release from its source (the crop management practice) to its sinks (i.e., agroecosystems and other ecosystems or components of ecosystems directly or indirectly affected by these releases), (3) select indicators that adequately describe the condition of the ecosystem affected directly or indirectly by crop production practices, (4) determine threshold values for the selected ecosystem indicators (i.e., values which should not be exceeded if irreversible changes in the affected ecosystems are to be avoided), (5) transpose the ecosystem threshold values to the farm level by retracing the impact pathways (from Step 2) backward to crop production itself, (6) derive farm‐level indicators that point to separate or combined agronomic practices that could cause irreversible changes in affected ecosystems, (7) determine farm‐level threshold values for management‐induced releases on the basis of ecosystem level threshold values, and (8) identify production schemes that adhere to the framework set by the farm‐level thresholds. From these production schemes the farmer can select those most in line with his available resources and objectives.

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Up to the latest versions of the German renewable energy act (EEG), there had been a constant growth of new biogas plants (BGPs). After reaching a stagnation in the last years, today the focus has shifted to improving the existing BGPs. Assuming that most plants have not reached the technical end of life, the question arises on how an operation can be realized beyond the initial EEG support period of 20 years. In addition, new legal and economic conditions require the implementation of adjustments, that is, “repowering measures.” Based on a method review, a plant‐specific model approach is presented to assess repowering measures for a wide range of BGPs differing in capacity, substrate mixture and agricultural structures. The techno‐economic model includes different performance indicators like levelized cost of electricity (LCOE) and temporal aspects like technical progress. Using a data set for BGPs in the state of Baden‐Wuerttemberg (Germany), results are illustrated for the different model modules and three repowering scenarios of an extended operation period of ten years. The scenarios regard different options to meet the requirements of the current EEG, namely the flexibilization and restrictions on energy crops, in comparison with a reference case. While in repowering scenarios, the number of plants decreases between 54% and 69% and the overall power capacity changes between −48% and 13% until 2035. The results further show a reduction potential in the specific area demand and GHG emission up to 12% and 24%, respectively. Technical progress, additional revenues and capacity premiums are shown to be an important factor for efficient substrate utilization, low LCOE and thereby the enabling of an extended operation period. The scenario results indicate that the agricultural areas for energy crop cultivation and the amount of manure used in BGPs will be reduced considerably, inducing new chances and challenges in the future.

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