Evaluating trends in yield and soil quality over 30 years of organically managed grass-clover ley in Norway

Abstract

Organically managed grass-clover leys are often claimed to improve soil quality and are considered as a cornerstone of sustainable agricultural practice. However, we lack long-term data to understand the effects of long-term organic management on soil quality and farm productivity. Therefore, in this study we evaluated soil organic matter (SOM) and nutrient status in relation to grass-clover ley yields after converting a ruminant feed farm to organic management. At Tingvoll research farm, organic milk production was established in 1989, replacing the previous conventional sheep farming. Records of purchased and sold materials and products were applied to calculate annual farm gate nutrient budgets. Since 1990, composite soil samples (0–20 cm depth) have been taken every 5–7 years for determination of SOM, pH, and soil nutrient status. On several fields, ley yields have been recorded annually. The mean air temperature increased during 1991–2021, while SOM concentration in the cultivated fields decreased overall from 10.3% to 7.8%, especially in soil with high initial SOM concentration. We observed a sharp decline in extractable phosphorus (P) following the conversion to organic farming, reflecting the changes in the farm nutrient budget. These shifts contributed to reduced dry matter yield of the grass-clover ley. Overall, the findings highlight long-term changes in soil fertility and ley productivity after the conversion to organic management, and the system capacity to sustain production while adapting to climatic and management challenges.

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