Short‐Term Effect of Different Agronomic Managements on Soil Carbon Fractions Content

ABSTRACT This research investigates the short‐term impact of different agricultural management strategies on soil organic matter (SOM), focusing on particulate organic matter (POM) and mineral‐associated organic matter (MAOM). The study assessed the effects of organic fertilisation (compost vs. digestate) and cover crop management (fixed cover crop species vs. succession of cover crop species vs. weedy fallow) in a 5‐year maize‐soybean rotation, using soil from a 7‐year forested area (FA) present in the same experimental site as a reference for comparison. The findings indicated that organic fertiliser or cover crop types alone did not significantly impact soil organic carbon (SOC). Instead, the combined use of compost and a succession of winter cover crop species resulted in significantly higher SOC content in the upper 40 cm of soil (11 g kg −1 ) compared to FA (7.6 g kg −1 ). While C‐POM remained unaffected by agronomic management (on average 2.1 g kg −1 ), C‐MAOM was significantly higher (+47.4%) under the combined compost fertilisation and cover crop succession compared to FA and to systems managed with compost and a fixed winter cover crop (on average 5.7 g kg −1 ). Total nitrogen content and stock did not differ significantly in the first 40 cm of soil among the agronomic strategies tested in the cultivated area. In contrast, compared to FA, significantly higher total nitrogen content and stock (+43.7% and +41.5%, respectively) were found in soils where different winter cover crop species successions were present, regardless of the type of organic fertiliser applied. Under field‐scale conditions and conventional tillage, these results indicate that short‐term changes in SOC are preferentially associated with MAOM rather than with POM, and emerge only when organic input quality and diversity are jointly optimised. In the experimental conditions, traditional agroecosystem management based on ploughing, coupled with organic fertilisation, did not significantly alter SOC compared to FA in the short‐term. Overall, the study suggests that optimising organic input quality and diversity can promote early MAOM formation, with potential implications for SOC sequestration strategies.