Field assessments of biotic and abiotic driving legume soil fatigue in pea (Pisum sativum L.) under Mediterranean conditions

Grain legumes play a strategic role in European agriculture by providing plant-based protein for human consumption and animal feed, while enhancing agroecosystem sustainability through biological nitrogen fixation and reduced dependence on mineral nitrogen fertilizers. However, an excessive frequency of grain legumes within crop rotations can lead to the onset of soil-borne constraints commonly referred to as “legume soil fatigue”. This complex phenomenon is thought to arise from the interaction of biotic stresses, such as soil-borne pathogens and pests, and abiotic stresses, including soil compaction, waterlogging, and heat stress, yet its underlying mechanisms remain poorly understood.

During the 2025 growing season, field investigations were conducted in 12 pea (Pisum sativum L.) fields across northern Italy to assess the occurrence of legume soil fatigue and to identify the underlying drivers associated with this phenomenon. The sites were characterized by predominantly loam soils. Field assessments were performed at crop emergence, flowering and harvest, and included measurements on pea plants (e.g. sowing depth, plant height, plant density, and root health), as well as soil properties (e.g. soil compaction, visual soil structure, and chemical analyses). Agronomic management practices were documented and a 10-year cropping history was reconstructed through farmer interviews to quantify the frequency of legumes, cereals, and other crops within rotation.

Preliminary analyses revealed that pea root damage was positively correlated with legume cultivation frequency (R² = 0.47, p < 0.001) and with the abundance of inactive rhizobia (R² = 0.61, p < 0.001), suggesting that frequent legume inclusion in crop rotations promotes root diseases and reduce nitrogen fixation efficiency. Conversely, a higher abundance of active rhizobia was associated with improved soil structure (R² = 0.61, p < 0.001). Among abiotic factors, soil compaction showed positive relationships with silt (R² = 0.64, p < 0.001) and sand content (R² = 0.53, p < 0.001), likely reflecting surface crust formation in loam soils, which can contrast seedling emergence and early root development.

Overall, these findings indicate that legume soil fatigue in pea cropping systems emerges from the combined effects of crop rotation intensity and soil physical constrains, with direct implications for root health and symbiotic nitrogen fixation. Ongoing work will integrate multi-country datasets and long-term field experiments to identify and characterize abiotic drivers (soil factors), biotic drivers (bacterial, fungal, nematode, and protist communities) and farm history factors associated with legume soil fatigue, thereby providing practical management guidelines for the sustainable expansion of legume-based cropping systems across Europe.