Sources

Feed EC targets on the EC page, for hydro, coco and soilless mixes:

Temperature correction uses 2% per °C, referenced to 25 °C [6].

1. Kroggel, M. and C. Kubota. 2018. Hydroponic Nutrient Solution Optimized for Greenhouse Tomato Production. Ohio State University Extension, HYG-1437.
2. Kubota Lab, Ohio State University. Indoor berry production: Fertigation.
3. Hort Americas. Hort Americas Hydroponic Fertilizer: leafy greens guidelines.
4. Hort Americas. Nutrient recipe for hydroponic greenhouse bell peppers.
5. Dunn, B. and H. Singh. 2017. Electrical Conductivity and pH Guide for Hydroponics. Oklahoma State University Extension, HLA-6722.
6. APHA. 1992. Standard Methods 2510: Conductivity. 18th ed.

The guide EC, ppm, and the 500 and 700 scales explained uses the same sources.

Crop presets on Recipes, in ppm (N-P-K-Ca-Mg), for hydro, coco and soilless mixes. Feed EC comes from the EC section above.

1. Hochmuth, G. and R. Hochmuth. Nutrient Solution Formulation for Hydroponic (Perlite, Rockwool, NFT) Tomatoes in Florida. UF/IFAS Extension, HS796, Table 1.
2. Hort Americas. Nutrient recipe for hydroponic greenhouse bell peppers, Table 1. N is nitrate plus ammonium; the mature K range is 270 to 300.
3. Kubota Lab, Ohio State University. Indoor berry production: Fertigation, Yamazaki formula at full strength.
4. Penn State Extension. Hydroponics Systems: Nutrient Solution Programs and Recipes, modified Sonneveld solution for herbs.

Soil has no preset. Use the Soil Test Calculator.

Targets the pH tool and the Fertigation Calculator set from the growing medium:

UMass sets alkalinity limits by container size (plugs 65, small pots 85, 4 to 5 inch pots 105, 6 inch pots and long-term crops 130 ppm), not by medium, so matching them to a medium is Bizon's. Below about 40 ppm alkalinity the tool calls water low in buffering, from UMass's minimum of 37.5 [1]. MSU puts the optimal substrate pH for most greenhouse and nursery crops at 5.4 to 6.4 [4].

1. UMass Extension. Water Quality for Crop Production.
2. UMass Extension. Soil Tests: Sampling and Interpreting Results of Greenhouse Soil Tests. Soilless media 5.5 to 6.0; mixes with 20% or more field soil 6.2 to 6.5.
3. Hort Americas. Hort Americas Hydroponic Fertilizer: leafy greens guidelines. Lettuce pH 5.4 to 5.8.
4. MSU Extension. Managing substrate pH of soilless substrates.

• Boom rate: gallons per acre = GPM × 5,940 ÷ (mph × nozzle spacing in inches) [1]. The metric form is the same formula in other units.
• Replace any nozzle more than 10% off the average of all nozzles [1], or more than 10% off a new nozzle's catalog output at the same pressure [2].
• On a 1/128-acre course, fluid ounces caught equal gallons per acre [2].

1. NC State Extension. Sprayer Calibration, 2019 Cotton Information, chapter 14.
2. Ohio State University Extension. Why should you calibrate your sprayer, and how? C.O.R.N. Newsletter 2020-11.

Feeding strengths on the simple calculator, in ppm of the leading nutrient (usually N):

Spoon measures assume about 5 g of soluble powder per level teaspoon, a Bizon estimate: a teaspoon is 4.9 mL, and soluble powders weigh about 1.0 to 1.2 g per mL.

1. Hochmuth, G. and R. Hochmuth. Nutrient Solution Formulation for Hydroponic (Perlite, Rockwool, NFT) Tomatoes in Florida. UF/IFAS Extension, HS796.
2. Penn State Extension. Hydroponics Systems: Nutrient Solution Programs and Recipes.
3. Jack's Professional (ICL). Product label, constant liquid feed guide. A fertilizer maker's guide.

Numbers on the soil test calculator:

Base saturation for Ca, Mg and K is shown without a target. Research does not support an ideal balance; see Wisconsin [8].

1. Culman, S., A. Fulford, J. Camberato and K. Steinke (2020). Tri-State Fertilizer Recommendations. Ohio State Bulletin 974. Build-up rates as quoted by Ohio's Country Journal.
2. Vossen, P. Changing pH in Soil. UC Cooperative Extension, Table 1.
3. Richards, L.A., ed. (1954). USDA Handbook 60. Classes as given in University of Delaware, Salt Measurements and Soil Classifications.
4. Lindsay, W.L. and W.A. Norvell (1978). Development of a DTPA soil test for zinc, iron, manganese, and copper.
5. Agriculture and Agri-Food Canada. Reclaiming saline soils (archived).
6. Iowa State University Extension. Late spring soil nitrate test.
7. ICL. Osmocote longevities. A fertilizer maker's tables.
8. Kelling, K.A. Base cation saturation ratios (paper). University of Wisconsin.

Numbers on the lime calculator:

1. Iowa State University Extension lime table, as quoted by Ask Extension (lb per 100 sq ft, top 6 inches, to pH 6.5).
2. Vossen, P. Changing pH in Soil. UC Cooperative Extension, Table 1 (pH 5.5 to 6.5).
3. Waltz, C. (2020). Lawns in Georgia: Selection and Species. UGA Bulletin 1533-1.
4. USDA NRCS. Seashore paspalum plant guide; UF, Florida Green (2005).
5. Virginia Tech Extension. 452-718; NCDA&CS, Note 4: Lawns, Gardens and Ornamentals.

Nitrogen on the lawn fertilizer calculator, in lb N per 1,000 sq ft per year (low / standard / high upkeep):

1. Purdue Turfgrass Science. Fertilizer Recommendations; AY-25.
2. Texas A&M AgriLife Extension. Fertilizing Texas Lawns, Table 1.
3. NC State Extension. Caring for Your Lawn and the Environment, Table 2; Oregon State, PNW Weed Handbook, turfgrass fertilization.
4. Virginia Tech Extension. 452-718.
5. UF/IFAS. Urban Turf Fertilizer Rule for Home Lawn Fertilization (EP353).

Seed rates on the grass seed calculator, in lb per 1,000 sq ft (new lawn / overseed), and days to germinate:

1. University of Tennessee Extension. Turfgrass Establishment: Seeding (W160-B).
2. Purdue Turfgrass Science. AY-25.
3. Oregon State University. Turfgrass Seeding Recommendations for the Pacific Northwest (PNW299).
4. University of Arkansas. Establishing Seeded Zoysiagrass (MP476).
5. Nebraska Extension. G1946; K-State, Planting buffalograss and controlling weeds.
6. USDA NRCS. Buffalograss plant guide.
7. Clemson HGIC. Overseeding with Ryegrass.
8. Purdue Turfgrass Science. Herbicide Delays After Seeding.

Limits on the irrigation water quality tool, in ppm unless marked:

1. Nelson, P.V. and D.A. Bailey, NC State. Water Quality, N.C. Flower Growers' Bulletin 39(3), 1994, Table 1.
2. Robbins, J.A., University of Arkansas. Irrigation Water for Greenhouses and Nurseries (FSA-6061), Table 1.
3. Ayers, R.S. and D.W. Westcot, FAO. Water Quality for Agriculture, Irrigation and Drainage Paper 29, Table 1.
4. Haman, D.Z., UF/IFAS. Causes and Prevention of Emitter Plugging in Microirrigation Systems (BUL258), Table 1.

Component figures on the soilless mix calculator: total porosity / water held / air, % by volume, and dry bulk density:

1. Fields, J.S., W.C. Fonteno and B.E. Jackson, NC State. Hydrophysical Properties, Moisture Retention, and Drainage Profiles of Wood and Traditional Components for Greenhouse Substrates. HortScience 49:827–832 (2014), Tables 1 and 2.
2. Bilderback, T.E. et al. Healthy Substrates Need Physicals Too! HortTechnology 15:747–751 (2005).
3. Evans, M.R., University of Arkansas. Greenhouse Management Online: Common Substrate Amendments.

DLI targets on the PPFD and DLI calculator, in mol/m²/day:

1. Torres, A.P. and R.G. Lopez, Purdue. Measuring Daily Light Integral in a Greenhouse (HO-238).
2. Mattson, N., Cornell CEA, in Hort Americas. Daily Light Integral: How Much Light Do I Need?
3. Kusuma, P., P.M. Pattison and B. Bugbee. From physics to fixtures to food: current and potential LED efficacy. Horticulture Research 7:56 (2020).
4. Rodriguez-Morrison, V., D. Llewellyn and Y. Zheng. Cannabis Yield, Potency, and Leaf Photosynthesis Respond Differently to Increasing Light Levels in an Indoor Environment. Frontiers in Plant Science 12:646020 (2021).

Numbers on the VPD chart, in kPa:

1. Allen, R.G., L.S. Pereira, D. Raes and M. Smith. Crop Evapotranspiration, FAO Irrigation and Drainage Paper 56, equation 11.
2. Greenhouse Management Online (Evans, Arkansas). Managing Vapor Pressure Deficit in Greenhouses, chapter 11.
3. Hort Americas. Understanding Vapor Pressure Deficit (VPD).
4. Corredor-Perilla, I.C., T.-H. Kwon and S.-H. Park. Elevated relative humidity significantly decreases cannabinoid concentrations while delaying flowering development in Cannabis sativa L. Frontiers in Plant Science 16 (2025).

Numbers on the lawn watering calculator:

1. Taylor, D. Watering Lawns and Other Turf. University of Minnesota Extension FS-02364-A.
2. Huang, B. Turfgrass Water Requirements and Factors Affecting Water Usage (USGA), Table 11.1, from Beard and Beard 2004.
3. FAO. Irrigation Water Management, Annex 2, basic infiltration rates.
4. UC Davis Center for Urban Horticulture. Landscape irrigation handout.
5. Michigan State University Extension. Summer Lawn Care (E3180).

Models on /degreedays:

1. Purdue Turfgrass Science
2. Kreuser & Soldat, University of Wisconsin-Madison (Crop Science)
3. Penn State Extension
4. Iowa State University Extension
5. Purdue University, Corn Hybrid Maturity
6. Nebraska Extension CropWatch
7. Iowa State University Extension
8. Iowa State University Extension
9. University of Wisconsin-Madison Extension
10. UConn Extension, Scheduling Sweet Corn Plantings
11. Utah State University Extension
12. Cornell IPM
13. NDSU Extension
14. Rutgers Plant & Pest Advisory
15. University of Delaware Extension
16. UC Agriculture and Natural Resources, Grapes for Home Gardeners (regions from Winkler et al. 1974)

Chill ranges and cold limits on /chillhours:

1. UF/IFAS Extension
2. Midwestern Regional Climate Center (Purdue; list from Raintree Nursery)