PS8-5. Effect of Defoliation Intensity on Cool-season Cover Crop Performance.

Abstract The integration of crop and livestock production is regaining global relevance as a strategy to enhance the sustainability of agricultural systems. Grazing annual cool-season cover crops (CC) effectively bridges these productions, providing critical ecosystem services such as carbon balance, nutrient cycling, water retention, enhanced soil structure and biological activity, and provisioning services through animal consumption. However, the magnitude of these benefits depends strictly on grazing management; overgrazing may negatively impact the production system and negate the advantages provided by the CC, while too much CC residues may affect next crop establishment efficiency. Grazing intensity is the primary factor determining the impact of livestock in an integrated system. Therefore, the objective of this study was to evaluate the effect of different defoliation intensities performed by mechanical cutting on cover crop yield (CCY), final height (CCFH), total harvested herbage mass (HHM), and final residue (FR) levels (all expressed in kg DM/ha). Experiment was carried out in four blocks each with three paddocks. An oat-vetch (Avena sativa L./Vicia villosa L.) mixture (70/30 ratio) was no-till seeded into wheat stubble at a target density of 170 plants/m2. Treatments consisted of three utilization intensities: two simulated grazing levels by mechanical cutting at 5 cm (T5) and 15 cm (T15) residual heights, and an uncut control (UC). Defoliation criteria, simulating a rotational grazing system, were based on the oat crop reaching the 3-leaf stage and 95% intercepted photosynthetically active radiation. The first cut was performed simultaneously for T5 and T15; subsequent cuttings depended on regrowth rates. Total CCY was calculated as the cumulative sum of each cut plus the FR, while UC was measured once at the end of the cycle. CCFH was determined before the last cutting of each treatment using a graduated ruler following a diagonal path across each plot (15 records per plot). Data were analyzed as a randomized complete block design using the ANOVA procedure of InfoStat (v.2020; Córdoba, Argentina). Cover crop yield was affected by treatment (P < 0.05), averaging 6,753 kg DM/ha for the defoliated treatments (T5 and T15) and 13,158 kg DM/ha for the UC (Table 1). In accordance with that, CCFH was higher in UC than in defoliated treatments. During the CC growing period, T5 and T15 were defoliated twice, and HHM for T5 was higher than T15 (P > 0.05), while FR was greater in T15 than T5, with UC being the highest (P < 0.05). As harvesting intensity acts as a key defining the balance between provisioning services (forage for animal consumption) and regulating services (soil cover and herbage residue), these results suggest the convenience of a moderate intensity to perform both goals. Further research is required to quantify the long-term trade-offs in integrated crop-livestock systems. For image description, please refer to the figure legend and surrounding text.