Closing Nutrient and Carbon Loops: Field‐Scale Demonstration That Biogas Digestate Enhances Soil Ecosystem Services and Crop Productivity

This on‐farm strip demonstration evaluated the response of maize and selected soil indicators to biogas digestate (DIG), a nutrient‐rich by‐product of anaerobic digestion, and to a low‐dose commercial humic product (BLK) after 3‐year production‐field conditions in southwestern Poland. The DIG treatment significantly increased fresh and dry matter yields (by 2.8 and 2.5 times, respectively) and enhanced soil properties, including total and labile carbon fractions, total nitrogen and available water capacity. In contrast, BLK showed only minor, non‐significant improvements in yields and soil properties. Digestate application improved both the quantity and quality of soil organic matter without increasing hydrophobicity, indicating its potential to support key soil functions such as nutrient cycling and water retention. These results highlight the dual role of DIG as both an effective fertiliser and a sustainable use of organic waste, supporting local nutrient recycling, rural resource sustainability within a circular bioeconomy framework. The findings are interpreted in terms of soil‐related ecosystem services, following the Common International Classification of Ecosystem Services (CICES V5.2), using indicators derived from field measurements. However, as treatments were applied to non‐randomised field strips without independent replication and differed in functional role and nutrient input, the results should be interpreted as site‐specific associations rather than strictly causal or directly comparable effects, while still providing valuable insights under practical farming conditions representative of commercial agriculture.