The average percentage change estimates for all 13 soil health and productivity parameters come from this peer-reviewed meta-analysis. The authors compiled paired treatment/control data from 269–281 published field studies across 38+ countries, then used one-sample t-tests and unbalanced analysis of variation (UANOVA) to identify which factors — climate type, soil texture, cover crop category, and cash crop type — most strongly determine how much each indicator responds. Those four factors became the structure of this calculator's five-step inputs. The companion dataset paper (Data in Brief 29, 105376) is fully open-access and includes the R code and raw data at github.com/jinshijian/SoilHealthCalculator. The original web tool was hosted by Virginia Tech's School of Plant and Environmental Sciences at soilhealth.spes.vt.edu.

Every species dropdown, C:N ratio, crude protein value, salinity tolerance, seeding depth, water use rating, and nitrogen-scavenging tier in Step 4 comes from the NRCS Cover Crop Chart — a compendium assembled by USDA-ARS from the Midwest Cover Crops Council, USDA-SARE, the USDA-NRCS PLANTS database, and peer-reviewed journal articles. The chart covers 50+ species across cool-season grasses, warm-season grasses, cool- and warm-season legumes, and broadleaf/brassica groups. Species modifiers applied to the base model values — for example, radish's strong effect on bulk density and infiltration, or hairy vetch's outsized nitrogen contribution — are derived from the trait ratings and C:N data in this chart. The chart is produced and freely distributed by the NGPRL in Mandan, ND.

The species insights shown after calculating — termination timing, allelopathy warnings, N credit guidance, cash crop compatibility notes, and C:N interpretation — are drawn from this USDA-SARE handbook. It synthesizes farmer trials, university extension research, and peer-reviewed studies to provide practical management guidance for each species. Key findings used here include: hairy vetch N credit ranges of 90–200 lb N/ac and its documented yield uplift in no-till corn; cereal rye allelopathic effects on soybean germination and appropriate termination windows; brassica bio-fumigant effects on nematodes and soilborne disease; the legume inoculation requirement for effective N fixation; and the 3-week termination buffer before planting for allelopathic species. The book is published by the Sustainable Agriculture Research & Education (SARE) program with funding from USDA-NIFA.