Forage Production in Challenging Soil Environments: Tall Wheatgrass in the Flooding Pampas of Argentina

Pasture-based livestock systems in Argentina’s Humid Pampas are increasingly confined to soils with shallow or mechanically restrictive horizons, limiting forage production even under favourable climates. Tall wheatgrass [Elymus elongatus (Host) Runemark] is one of the few forage species capable of enduring these environments. To better understand forage yield drivers, we assessed the impact of soil restrictions, water, and nitrogen availability. Shoot biomass, water and nitrogen uptake, and water and radiation use efficiency (WUE, RUE) were evaluated during autumn, spring, and summer over two years. Experimental factors included edaphic environment (differing in water-holding capacity and A-horizon thickness), water availability (rainfed vs. irrigated to potential evapotranspiration), and nitrogen (0 vs. 300 kg N ha−1). Yield was challenged by the edaphic environment even under non-limiting resource supply. Water was clearly linked to yield only during summer stressful conditions, while nitrogen uptake was ever present through its impact on canopy development, thereby influencing WUE and RUE. This study demonstrates that forage yield is fundamentally constrained by the edaphic environment, with the magnitude of this response aligning with soil harshness and climatic drivers of yield.