Ecosystem functions in mixed cropland-grassland systems influenced by soil legacies of past crop cultivation decisions

As global food demand continues to grow, private landowners and agricultural managers have increased incentives to convert grasslands to expand crop production. These conversions are increasingly occurring on marginal soils susceptible to rapid degradation, which threatens delivery of diverse bundles of ecosystem goods and services (EGS). A growing number of studies have demonstrated that previous land management decisions continue to effect current soil ecosystem functions in the long-term (i.e., soil legacies persist after previous management has ceased). Such legacies could further alter EGS deliveries, especially in mixed-use agroecosystems (grass and croplands) that are susceptible to large, rapid changes in land use. The objective of this work was therefore to identify potential soil legacy effects and recovery time delays after land transformation and to place those effects in the context of EGS tradeoffs. Our overall hypotheses were that soil legacies can be traced back to management's EGS prioritization, that soil legacies persist due to the nature of land use (grass versus cultivation) and the time (years) under management, and that anthropomorphic manipulation from cultivation creates specific kinds of soil legacies. Using a systems approach that integrated ecosystem indicators, physical soil data, and human dimensions, we tested our hypotheses in South Dakota (USA), along the 100th Meridian (west), where recent and rapid cultivation expansion has reached historic highs. We conducted intensive interviews of four private land managers to identify historical land transformations, current goals, and strategies employed to achieve those goals on varying sites within their operations (nine grassland sites, nine cultivated sites; n = 18). Ecosystem assessments were conducted on each site using the US interagency assessment protocol Interpreting Indicators of Rangeland Health. Field aggregate stability and soil organic matter using loss-on-ignition were also measured. We found that (1) soil legacies continued to be detectable up to 20 yr after land transformation; (2) producers' personal values of EGS were directly linked to observed land uses and ecosystem ratings; and (3) opportunities for reintroducing grasses into crop rotations or crop-livestock integration could likely improve EGS delivery from converted lands while enhancing rural economic outcomes at a low- to no-cost trade-off between ecosystem functions.