Newly established, multifunctional woody polycultures preserve agroforestry soil health benefits of a widespread U.S. land retirement program

Abstract

Soil health degradation within intensively managed annual crop systems threatens the long-term economic sustainability of maize- and soybean-dominated production regions like the U.S. Corn Belt. While Conservation Reserve Program (CRP) efforts to perennialize portions of farmland to improve soil health have been largely successful, many landowners intend to return CRP land to high revenue maize and soybean cultivation. The CRP could be a pathway for a regionally tailored and profitable form of agroforestry focused on fruit and nut production potential, known as multifunctional woody polycultures (MWPs). In theory, MWPs should provide similar soil health benefits as CRP agroforestry, as soil health benefits are generally robust across agroforestry practices. We conducted a study in the heart of the U.S. Corn Belt to compare soil health responses between newly established (<10 years) CRP and MWP agroforestry systems and adjacent annual crop production fields. Because organic inputs from plant litter and roots are more consistent under untilled perennial vegetation systems compared to intensively managed annual crop systems, we hypothesized that CRP and MWP would entail similar enhancements to physical, soil organic matter (SOM), and biological soil health. Our results indicate establishing untilled, perennial CRP and MWP systems can quickly improve physical and biological soil health relative to annual crop production, based on decreased soil bulk density, greater soil water infiltration, and increased soil enzyme activity. Unexpectedly, CRP and MWP elicited divergent SOM responses. Notably, only MWP increased surface soil organic carbon stocks relative to annual crop fields, likely reflecting species-variant plant biomass growth rates. Our study demonstrates MWPs can manifest similar improvements to physical and biological soil health as CRP agroforestry on a relatively short timescale. The sensitivity of transition-state SOM responses between CRP and MWP demonstrates the importance of woody perennial selection to maximize specific soil health outcomes.