Self-cover cropping systems and the plusquam-annual: new paradigms for sustainable food production.

Annual grain production is vital for food security, but fallow periods punctuating annual crop cultivation are environmentally problematic.While cover cropping offers a solution, implementation carries significant practical hurdles.Here we introduce self-cover cropping systems -achieved through post-harvest crop regrowth -to deliver cover crop-like ecosystem services with fewer challenges.As a corollary, we define plusquam-annuals (meaning "morethan annuals") as a distinct, novel crop growth habit characterized by a single grain harvest followed by regrowth.We suggest viable self-cover cropping cereals may already exist and offer a conceptual framework that invites empirical exploration with both applied and theoretical significance. BackgroundAs modern agricultural systems are re-examined through the lens of unprecedented population growth and changing climates, production systems are being reimagined with an explicit intention to consider productivity in tandem with other goals such as minimizing non-renewable resource use and increasing environmental services [1][2][3][4] .Annual grain production systems, which are scaffolded by cereal crops such as wheat (Triticum aestivum), rice (Oryza sativa), and maize (Zea mays), play a crucial role in global food security.While incredibly productive, annual crops pose significant challenges to long-term sustainability in the form of decreased soil productivity 5,6 , compromised water bodies and drinking water 7,8 , greenhouse gas emissions 9 , and declines in biodiversity 10 .Many of these undesirable outcomes stem from the fallow periods that punctuate annual crop production [11][12][13] .As such, several holistic agricultural paradigms (e.g., regenerative, organic) encourage the reduction of fallow periods in agriculture through, among other practices, the use of cover crops [14][15][16][17] . The trouble with cover cropsCover cropping is a well-established conservation practice in agriculture [18][19][20] .Presently, there is a strong focus in cover cropping science and policy around its role in reducing soil erosion and nitrate leaching during winter fallow periods 21,22 .We therefore use winter cover cropping as the setting for this Perspective, but the concepts presented can be extrapolated to other contexts.Establishment of winter cover crops is associated with direct costs to the producer in the form of seeds, fuel, and time, and indirect costs through potential risks to cash crop performance [23][24][25] .While long-term agronomic benefits from cover crop use may offset these costs, the benefits are hard to quantify in the short-term, tenuous, and are not easily priced 26- 29 .Voluntary adoption of winter cover cropping therefore remains low 30,31 , and