Flex Maize Hybrid Performance in Cover-Cropped Systems: Interactive Effects of Tillage and Nitrogen Fertilization

Synchronizing nitrogen (N) release from cover crop residues with maize N demand is essential for reducing reliance on synthetic fertilizer while maintaining yield in semi-arid, irrigated production systems. Optimizing N fertilizer rates is crucial for sustaining maize yield while reducing production costs and environmental impacts. A three-year study (2023–2025) in Western Colorado evaluated three flex maize hybrids (Zea mays L.) planted into three preceding cover crop species (hairy vetch (Vicia villosa Roth), cereal rye (Secale cereale L.), and a hairy vetch + cereal rye mixture), two tillage systems (strip-till vs. conventional tillage), and two N fertilizer rates (100% vs. 80% of the recommended rate). Grain yield, ear characteristics, and agronomic efficiency varied significantly among hybrids: the high-flex hybrid DKC 105-33 RIB consistently outyielded the low-flex hybrid DKC 48-34 RIB by 1.5–2.5 Mg ha−1 across years and maintained higher productivity. The hybrid × N interaction was not significant, suggesting that yield responses to reduced N were statistically similar across hybrids. Strip-tillage did not significantly affect grain yield in any year, indicating that reduced tillage can be implemented without a yield penalty, although it modestly changed leaf area index, plant population density, and harvest index. Reducing the N rate from 224 to 179 kg N ha−1 decreased grain yield, harvest index, and population density, but did not affect plant height, leaf area index, ear density, or 100-kernel weight; Cover crop N supply ranged from 20.3 to 24.7 kg N ha−1 and was governed primarily by tissue N concentration rather than total biomass; hairy vetch supplied the greatest N credit despite producing only about one-third the biomass of cereal rye. Collectively, these results demonstrate that pairing high-flex maize hybrids with cover crop and reduced-tillage management is a viable strategy for optimizing maize productivity while reducing synthetic N inputs in semi-arid, irrigated cropping systems.