Materials and Methods Corn (Zea mays L.) was selected for our study due to its pre-eminence as a food crop in North America and globally. Corn is planted on 39.9% of all crop acres (NASS, 2017), or 4.8% (37.1 million ha) of the terrestrial land surface of the contiguous 48 states. In 2012, it generated 30.3% ($64,319 billion) of all gross crop value in the US (NASS, 2017). Nearly 100% of cornfields are treated annually with insecticides (NASS, 2017). We used a matrix of specific production practices (Table 1) to define each farm into one of two systems (regenerative or conventional). The most regenerative systems (n = 40 fields on 10 farms) used mixed multispecies cover crops (ranging from 2–40 plant species), were never-till, used no insecticides, and grazed livestock on their cropland. The most conventional farms practiced tillage at least annually (36 fields on eight farms), applied insecticides (as GM insect-resistant varieties and neonicotinoid seed treatments), and left their soil bare aside from the cash crop. Reference town Farm locations (latitude, longitude) Cover crop (yes: 1; no: 0) Insecticide (no: 1; yes: 0) Other pesticides (no: 1; yes: 0) Tillage (yes: 0; no: 1) Grazed corn field (yes: 1; no: 0) Composite rank score Bladen, NE 40.31971, −98.57358 yes no yes no no 3 Bladen, NE 40.33703, −98.56301 no yes yes yes no 0 York, NE 40.63054, −97.66534 yes no yes no no 3 York, NE 40.97390, −97.49031 no yes yes yes no 0 Bismarck, ND 46.85280, −100.60131 yes no no no yes 5 Bismarck, ND 46.85280, −100.35145 no yes yes no no 1 Bismarck, ND 46.81734, −100.51257 yes no yes no yes 4 Bismarck, ND 47.14250, −100.19720 no yes yes no no 1 White, SD* 44.42572, −96.58806 yes no no yes no 3 White, SD 44.41155, −96.60008 no yes yes yes no 0 Pipestone, MN* 44.11446, −96.32468 yes no no yes no 3 Pipestone, MN 44.12416, −96.36422 no yes yes yes no 0 Toronto, SD 44.59248, −96.57923 yes yes yes no no 3 Toronto, SD 44.57960, −96.58367 no yes yes yes no 0 Gary, SD* 44.80565, −96.34708 yes no no yes yes 4 Gary, SD 44.80689, −96.35465 no yes yes yes no 0 Arlington, SD 44.41566, −97.18795 yes no yes no yes 4 Arlington, SD 44.42644, −97.25077 no yes yes yes no 0 Lake Norden, SD 44.58976, −97.08649 yes yes yes no yes 3 Lake Norden, SD 44.55.6839, −97.243820 no yes yes yes no 0 DOI: 10.7717/peerj.4428/table-1 Soil organic matter, insect pest populations, and corn yield and profit were assessed for each field. Soil cores (8.5 cm deep, 5 cm in diameter; 30 g of soil each; n = 4 samples per field that were made a composite sample; only one field was sampled per farm- selected by the producer- and two farms were omitted due to adverse weather during the sampling event) were collected at least 10 m from one another during anthesis. Samples were cleaned of plant residue, ground, and dried to constant weight at 105 °C. Particulate soil organic matter (POM) was determined by screening each sample (soaked in 5 g L−1 aqueous hexametaphosphate) through 500 um (course POM) and 53 um (fine POM) sieves and then applying the loss on ignition (LOI) technique (Davies, 1974). Insect pests were enumerated through dissections of all aboveground plant tissues (25 plants per field). Major pests of corn (rootworm adults, caterpillar pests, and aphids) are all present in cornfields at this crop developmental stage (Lundgren et al., 2015), and this was substantiated in the observations in this study as well. Yields were gathered from three randomly selected 3.5 m sections of row from each field. Gross revenue for each field were considered as yield and return on grain, and additional revenue streams (e.g., animal weight gain resulting from grazing). Total direct costs for each field were calculated based on the costs of corn seed, cover crop seed, drying/cleaning grain, crop insurance, tillage, planting, fertilizers, pesticides, and irrigation.

Conclusions The farmers themselves have devised an ecologically based production system comprised of multiple practices that are woven into a profitable farm that promotes ecosystem services. Regenerative farms fundamentally challenge the current food production paradigm that maximizes gross profits at the expense of net gains for the farmer. Key elements of this successful approach to farming include By promoting soil biology and organic matter and biodiversity on their farms, regenerative farmers required fewer costly inputs like insecticides and fertilizers, and managed their pest populations more effectively. Soil organic matter was a more important driver of proximate farm profitability than yields were, in part because the regenerative farms marketed their products differently or had a diversified income stream from a single field.