Compost Atlas — Sources

Soil data

USDA NRCS Soil Data Access (SSURGO)

Provides the live soil profile at any US coordinate — map unit, component, horizon-by-horizon pH, organic matter, CEC, bulk density, sand/silt/clay percentages, drainage class. Queried on demand for every Calculate request; the calculator does not store soil data.

Compost characterization methods

USCC TMECC — Test Methods for the Examination of Composting and Compost

The standardized analytical methods that every reputable compost lab (A&L Western, Control Labs, ANR Analytical, and similar TMECC-compliant labs) follows. Defines how moisture (TMECC 03.09), bulk density (03.01), pH (04.11), total elementals via acid digest (04.05), sulfate-S (04.06), organic matter (05.07A), calcium carbonate equivalent (04.08), stability (05.08-B), and electrical conductivity (04.10) are measured. The calculator expects values exactly as TMECC reports them; the input form labels each field with the underlying method.

90-day plant-available nutrient delivery

Compost Nutrient Substitution Report (internal technical memo, May 2026)

The substitution-ratio framework that converts a compost's total nutrient content into the fraction that becomes plant-available over the first 90 days. Synthesizes first-order N mineralization kinetics from Hartz & Bottoms (2010), Sullivan et al. (2003), and PNW EM 9304; accounts for C:N ratio (12 → 20) and application method (incorporated vs. surface) effects on nitrogen availability.

Crop nutrient demand (90-day window)

OSU Extension — Pacific Northwest Crop Fertilizer Guides

Per-crop nitrogen, phosphorus, potassium, and sulfur demand at typical commercial yields. Specific guides cited: PNW 611 (field corn), EM 8903 (processing tomato), EM 8918 (sweet corn), FG 30 (lettuce), FG 63 (broccoli), FG 79 (carrot), FG 80/82/84 (cole crops), EM 8963 (winter wheat), EM 9086 (alfalfa), EM 9099 (almond), EM 9304 (residual N decay).

PNW Crop Fertilizer Guide — consolidated reference set (Aug 2017)

Pacific Northwest Extension's tab-separated reference dataset compiling pH-min/max, N rates, and soil-test-stratified P/K/S rates for 39 crops. Provides the new preferred-pH window field for each crop and expands the demand database to 36 crops total (was 12). The published guide is a joint OSU / WSU / UI Extension product distributed via the Western Plant Diagnostic Network.

UC ANR — University of California Agriculture & Natural Resources

California-specific crop production manuals for strawberry, avocado, almond, and table grape. Calibrates the demand database to CA Central Valley and Central Coast yields.

NRCS Practice Standard 590 (Nutrient Management)

Federal nutrient-management framework. The calculator's nutrient-balance presentation follows the 590 convention of comparing what's delivered against documented crop demand.

Agronomic convention

Western Fertilizer Handbook (CPHA, 9th ed.)

Source for the elemental-to-oxide conversion factors used when the calculator reports P, K, Ca, Mg in agronomic-convention oxide form (P₂O₅, K₂O, CaO, MgO).

CDFA FREP — Fertilizer Research & Education Program

California Department of Food & Agriculture peer-reviewed research underpinning sulfate-S handling and CA-specific nutrient-budget conventions.

Soil-test (optional) — methods & lab examples

SSURGO does not report plant-available nutrient pools. When the user supplies a recent soil test, the calculator overrides the SSURGO pH with the lab-measured value and adds a soil baseline + compost delivery row to the crop-demand card. Any TMECC- or NAPT-participating soil-fertility lab works; the calculator is vendor-neutral.

Soil-pH (1:1 water or saturated paste)

Standard methods for the Examination of Soils, Sparks (Ed.), SSSA Book Series No. 5. The 1:1 water and saturated-paste readings are the two most common lab pH conventions; either is accepted as a baseline override.

Olsen-P (NaHCO₃ extract) · CA / arid-soil convention

Olsen et al. 1954, USDA Circular 939. Reported by UC ANR Vegetable Production Series and the CDFA FREP soil-test guidelines as the appropriate P extract for alkaline / arid California soils.

Bray-P (acid extract) · PNW / acid-soil convention

Bray & Kurtz 1945, Soil Science 59:39–45. OSU Extension EM 9099 and PNW 678 use Bray-P for acid soils west of the Cascades.

Exchangeable K (ammonium-acetate extract)

Brady & Weil, The Nature and Properties of Soils, 15th ed., Ch. 14. NH₄OAc-extractable K is the field-standard first-season K pool across both CA and PNW labs.

Sulfate-S (mono-calcium-phosphate extract)

Recommended Chemical Soil Test Procedures for the North Central Region (NCERA-13). Reports the plant-available SO₄²⁻ pool directly.

DTPA-extractable micros (Zn, Cu, Mn, Fe)

Lindsay & Norvell 1978, SSSA Journal 42:421–428. The standard Western-US micronutrient extract; correlates with first-season uptake.

Hot-water-soluble Boron

Berger & Truog 1939, Industrial & Engineering Chemistry, Analytical Edition 11(10):540–545. The field-standard B test across both CA and PNW labs.

Conversion convention (ppm → lb/ac)

Western Fertilizer Handbook (CPHA, 9th ed.), Ch. 4: soil mass (lb/ac) ≈ bulk_density (g/cm³) × depth (in) × 217,778, so 1 ppm at 6-in depth and BD ≈ 1.4 g/cm³ ≈ 1.83 lb/ac. The familiar field heuristic "1 ppm ≈ 2 lb/ac at 6 in" is the upper bound of that range. P-elemental and K-elemental are then converted to P₂O₅ / K₂O so the rows line up with the crop-demand values.

Lab examples (representative, not endorsements)

Any TMECC- or NAPT-participating soil-fertility lab works. Western-US labs include A&L Western Laboratories (Modesto, CA), Ward Laboratories (Kearney, NE), ANR Analytical (UC Davis), Spectrum Analytic (Washington Court House, OH), Servi-Tech (Dodge City, KS), and Brookside Laboratories (New Bremen, OH). Pick whichever your operation already uses — the calculator does not weight one lab over another.