Harvested perennial grasslands provide ecological benchmarks for agricultural sustainability

Perennial vegetation can provide multiple ecosystem services essential for sustainable production more effectively than production systems based on annual crops. However, the ability of annually harvested, unfertilized perennial systems to sustain long-term yields while also maintaining ecosystem services has not been widely studied. Here we compare the impacts of harvested perennial grass and annual crop fields on ecosystem functioning in KS, USA. Despite the lack of mineral fertilizer applications, the aboveground harvests of perennial fields yielded similar levels of N compared to those of conventional high-input wheat (Triticum aestivum) fields and at only 8% of the in-field energy costs. Their 75-yr cumulative N yield per ha was approximately 23% greater than that from the region's wheat fields. In terms of aboveground food webs, perennial fields harboured greater numbers and/or diversity of insect pollinators, herbivores and detritivores. Belowground, perennial grass fields maintained 43 Mg ha^-1 more soil carbon and 4 Mg ha^-1 more soil nitrogen than annual crop fields in the surface 1 m. Soil food webs in perennial fields, as indicated by nematode communities, exhibited greater food web complexity and stability than did those in annual crop fields. In surrounding watersheds, increased annual cropland was correlated with higher riverine nitrate-nitrogen levels. Given their benefits, harvested perennial grasslands provide valuable ecological benchmarks for agricultural sustainability.