Effect of preceding integrated and organic farming on ¹⁵ N recovery and the N balance, including emissions of NH ₃ , N ₂ O, and N ₂ and leaching of NO ₃ ⁻

Abstract. Ecological intensification strategies in agriculture, including organic fertilization and diversified crop rotations, aim to reduce nitrogen (N) losses to the environment. However, studies on N allocation and loss on adjacent sites with the same pedoclimatic conditions but different management histories, i.e. organic farming (OF) with frequent legume cultivation and occasional organic fertilizer input, compared to integrated farming (IF) with synthetic and organic fertilizers, have remained scarce. Understanding how these systems differ in their N dynamics is essential for improving nutrient management strategies, mitigating environmental impacts, and guiding sustainable agricultural practices. Here, we quantified field N losses (ammonia, nitrous oxide, dinitrogen, and nitrate leaching), total N balances, and 15N-labelled cattle slurry allocation to soil and plants of two adjacent sites over a 2-year cropping sequence. While IF had resulted in significantly higher pH and soil organic carbon and N content, the emissions of ammonia, nitrous oxide, and dinitrogen after cattle slurry application as well as nitrate leaching were not significantly different across the two farming techniques. Ammonia losses were low for all cultivation periods, indicating that drag hose application and manure incorporation successfully mitigate ammonia emissions. High 15N fertilizer recovery in plants and soil, along with a low share of unrecovered 15N, agreed well with the low directly measured N losses. On average, 15N recovery was lower for OF (85 % versus 93 % in IF), likely due to unaccounted N2 emissions, which could only be measured within 2 weeks after fertilizer application, but the high spatial variability of 15N recovery may have turned this difference insignificant. Significantly higher harvest biomass N for IF demonstrated that management history affected productivity through increased soil organic matter mineralization. Due to the higher productivity, the cumulative N balance across all cultivation periods was neutral within the limits of the measurement uncertainty for IF (−8 ± 15 kg N ha−1), indicating an optimized N management. For OF, the N balance across a single cultivation period ranged from −19 to 41 kg N ha−1; thus, the observations of a single cultivation period were inconclusive. The cumulative positive N balance (48 ± 14 kg N ha−1) across all cultivation periods for OF suggests that more frequent organic fertilizer additions could increase soil N (and carbon) stocks and finally improve yield. However, the positive N balance, coupled with lower 15N recovery for OF, also points to a higher likelihood of unaccounted N losses, which would, in turn, slow down the accumulation of soil N and C over time.