Yields of Annual and Perennial Energy Crops in a 12‐year Field Trial

CORE IDEAS: A long‐term field trial of important perennial and annual energy crops was conducted. Maize is most high yielding of biomass with high N inputs. Miscanthus is most high yielding of biomass without or with moderate N inputs. In crop rotations, no‐till practice with less input does not reduce the productivity. Nitrogen input is more important in annuals than perennials to maintain the yield level. To find an energy cropping system with low input and high productivity, a 12‐yr field trial was conducted in Southwest Germany with perennial crops, and monocropping or rotation of annual crops. The perennials were willow (Salix schwerinii E. Wolf × viminalis L.) short rotation coppice, miscanthus (Miscanthus × giganteus Greef et Deu.), and switchgrass (Panicum virgatum L.). The monocropped annual was maize (Zea mays L.), and the rotation was oilseed rape (Brassica napus L. ssp. oleifera)–wheat (Triticum aestivum L.)–triticale (Triticale × triticosecale Wittmack). The rotation was split into tillage with moldboard plow or no‐till. These systems were implemented with three N fertilization levels. Annual yield trend in years, accumulated yields of biomass, and gross energy were compared across N levels between perennials and annuals, and between tillage managements. Among these cropping systems, maize (18.5 Mg ha⁻¹ yr⁻¹) and miscanthus (18.3 Mg ha⁻¹ yr⁻¹) were most productive. Without N fertilization, miscanthus was most productive (13.6 Mg ha⁻¹ yr⁻¹). In the long run, N fertilization significantly increased the yields of all systems. The long‐term yield trends of the perennials were relatively stable, while the annuals without N fertilization showed a prevailing trend of yield decrease. No‐till did not significantly lower the yield compared to plowing (8.7 vs. 9.3 Mg ha⁻¹ yr⁻¹). Generally, the perennial systems produced higher gross energy yield compared to the annual systems under comparable N fertilizations. Particularly miscanthus gained high yields even with moderate to no N inputs.