Cristina Mori Alvez ^1* Oswaldo Ernst Benech ² Pablo González Barrios ³ Carlos Perdomo Varela ¹

• ¹ Department of Soil and Water, Faculty of Agronomy, University of the Republic, Montevideo, Uruguay
• ² Department of Crop Production, Faculty of Agronomy, University of the Republic, Montevideo, Uruguay
• ³ Departamento de Biometría, Estadística y Computación,Facultad de Agronomía, Universidad de la República, Paysandú, Uruguay

The shift in Uruguayan agriculture to no-till farming and more intensive agricultural practices, moving from crop-pasture (CP) systems to continuous cropping (CC) rotations, has disrupted biological nitrogen fixation (BNF). However, this change has not reduced the soil organic carbon (SOC) balance under no-till management under diversified cropping sequences that include C4 species, so the impact of this conversion on productivity and sustainability has yet to be noticeable insignificant across the system as a whole. This study, conducted within a long-term experiment (LTE), compared wheat productivity under no-till crop conditions for two systems: the first crop seeded after the perennial pasture phase in CP rotation and wheat in continuous annual cropping (CC rotation) in a rainfed environment. The variables measured were included soil nitrogen (N) concentration, wheat grain yield (WGY), grain protein concentration (GPC), and N use efficiency (NUE) by wheat over three seasons. The experimental treatments included four N fertilizer levels evaluated at each rotation system. The comparison between the two rotation systems revealed that CC consistently outperformed CP in terms of WGY, with an average of 2425 vs. 1668 kg ha -1 . Grain PC varied between rotations and N rates, with CP generally showing a higher GPC (on average, 10.48 vs. 10.92 %). Nitrate-N levels at tillering correlated positively with WGY and negatively with GPC, but the relationship differed by rotation. Soil NUE indices varied between rotations, with CC generally showing higher efficiencies. The study's findings highlighted the potential of CC rotation, especially when including C4 species in the crop sequence, to achieve higher wheat productivity in the short term due to healthier soil conditions compared to than the succeeding wheat seeded after post-pasture in CP. In conclusion Additionally, our study highlights that the effect of the previous crop on yield and NUE by in wheat was more relevant than the expected residual effect of the pasture phase in CP, mainly driven by primarily due to the quality of residues and the temporary adverse effects of soil compaction caused by livestock trampling.