Agronomic and economic responses of reduced‑lignin and conventional alfalfa to potassium

Abstract

Lignin‐modified (reduced‐lignin) alfalfa ( Medicago sativa L.) cultivars offer improved forage digestibility but may differ from non–lignin‐modified (conventional) cultivars in nutrient requirements. This study evaluated the effects of potassium (K) fertilization on stem production, forage accumulation, K uptake, forage nutritive value, and profitability in a reduced‑lignin cultivar (‘Hi‑Gest 360’) and a conventional cultivar (‘AFX 457’) under irrigated semi‑arid conditions in Wyoming. Treatments consisted of four annual K ₂ O rates (0, 50, 100, and 150 lb ac ⁻¹ per year) applied to an established stand over 2 production years. A significant K × cultivar × harvest frequency × year interaction affected forage accumulation and K uptake. In 2020–2021, AFX 457 achieved maximum yield (7335 lb dry matter [DM] ac ⁻¹ per year) and K uptake (280 lb K ac ⁻¹ per year) at 150 lb K ₂ O ac ⁻¹ per year, whereas Hi‑Gest 360 showed the highest response at 100 lb K ₂ O ac ⁻¹ per year, producing 7308 lb DM ac ⁻¹ per year and 281 lb K ac ⁻¹ per year. Forage nutritive value was not affected by K ₂ O rate or cultivar. Tissue K concentrations exceeded the agronomic sufficiency range (2%–2.5%) and surpassed the 3% dairy nutritional threshold at all application rates, including the unfertilized control. Economic analysis showed that intermediate K ₂ O rates (50–100 lb ac ⁻¹ per year) provided the highest profit margins for AFX 457 (∼$62–$63 ac ⁻¹ per year), with 100 lb K ₂ O ac ⁻¹ per year being optimal for Hi‐Gest 360 (∼$70 ac ⁻¹ per year). Results demonstrate that cultivar‑specific K management improves agronomic performance and profitability, even in soils with moderate to high exchangeable K, supporting more efficient alfalfa production.