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

Stanford & Smith (1972), Nitrogen mineralization potentials of soils (Soil Sci. Soc. Am. J. 36:465–472)

Establishes the first-order kinetic model describing how organically-bound nitrogen becomes plant-available over a growing season.

Gale, Sullivan, Cogger, Bary, Hemphill & Myhre (2006), Estimating plant-available nitrogen release from manures, composts, and specialty products (J. Environ. Qual. 35:2321–2332)

Incubation/field basis for how much compost nitrogen mineralizes in the first season, and how that shifts with compost maturity and C:N ratio.

Sullivan, Bary, Nartea, Myhre, Cogger & Fransen (2003), Nitrogen availability seven years after a high-rate food-waste compost application (Compost Sci. Util. 11:265–275)

Long-term record of residual nitrogen release in the years following application, informing multi-year carryover.

Cabrera, Kissel & Vigil (2005), Nitrogen mineralization from organic residues (J. Environ. Qual. 34:75–79)

Temperature dependence of soil nitrogen mineralization, used to relate laboratory rates to California growing-season soil temperatures.

Eghball (2002); Eghball, Ginting & Gilley (2004), residual effects of manure and compost (Agron. J. 94:128–135; 96:442–447)

Multi-year residual nutrient and soil-property effects of repeated compost and manure applications.

Sharpley (1996): Availability of residual phosphorus in manured soils (Soil Sci. Soc. Am. J. 60:1459–1466)

Basis for how compost phosphorus carries over and becomes available relative to soluble fertilizer phosphorus.

Whalen (2014): Managing soil biota-mediated decomposition and nutrient mineralization in sustainable agroecosystems (Adv. Agric. 2014:384604)

Potassium release from compost is largely dissolution-driven rather than mineralization-limited.

Western Fertilizer Handbook, 9th ed. (California Plant Health Association)

Reference for secondary- and micronutrient behavior and the standard oxide reporting conventions (P₂O₅, K₂O, CaO, MgO).

Crop fertilizer rates

The crop figures are extension fertilizer rates, the pounds per acre a grower applies, not the nutrients the crop takes up. A rate already credits a typical soil supply and allows for fertilizer losses, so it can sit far from uptake: the lettuce P₂O₅ rate is 120 lb/ac against about 20 lb removed in harvest. Compost delivery is therefore read as the share of the fertilizer program it replaces. PNW guide crops carry the medium soil-test rate as a full-season total; almond and winter wheat are scaled to the 90-day window. A crop with no published rate for a nutrient (sulfur for asparagus, blueberry and spinach) shows no comparison for it.

OSU Extension: Pacific Northwest Crop Fertilizer Guides

Per-crop nitrogen, phosphorus, potassium, and sulfur rates by soil-test level. Specific guides cited: PNW 611 (irrigated alfalfa), EM 8903 (blackberry, raspberry), EM 8918 (blueberry), FG 30 (crimson clover, vetch, field peas), FG 63 (pasture), FG 79 (hops), EM 8963 (winter wheat), EM 9086 (perennial ryegrass seed), EM 9099 (tall fescue seed), PNW 546 (onion), WSU EB 1871 (potato), and the OSU vegetable production guides for the remaining vegetables. 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 38 crops. Provides the preferred-pH window field and the medium soil-test rates for 24 of the 36 crops, and the P and K soil-test bands where the source guide names its lab extract or follows the OSU regional convention (P bands for 21 crops, K bands for 7). 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 rate 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 rates.

Maas and Grattan (1999), crop salt tolerance

E.V. Maas and S.R. Grattan, "Crop yields as affected by salinity," in Agricultural Drainage, Agronomy Monograph 38. Reprinted as Table A1.1 in FAO Irrigation and Drainage Paper 61, Annex 1. Each threshold is the seasonal-average saturated-paste ECe (dS/m) at which yield first declines, and the slope is the percent yield loss per dS/m above that threshold. The value is stored on the crop for the product the table measured (fruit, forage, shoot, or root). Capacity mode still uses the tolerance of the crop that follows the application window, because wheat grain and wheat forage are different numbers in the same table. A crop with no published threshold is left blank. Avocado, brussels sprouts, cauliflower, and raspberry are rated in the table but have no threshold or slope. Blueberry, crimson clover, hops, pasture, and winter squash are not in the table, and a nearby crop was not substituted.

Crop harvest removal (Compost Capacity)

How the defaults are set

The phosphorus limit in Compost Capacity is built on annual crop removal: the N, P2O5 and K2O that leave the field in the harvested product, with residue returned. Each crop carries one published removal value at a representative California or Western yield, stated with the crop; most yields are USDA NASS California three-year means. A custom rotation adds the removal of each crop it names (one harvest of each a year), and any value can be replaced with the grower's own removal or yield. Radish has no default because no Western public source reports its yield by weight.

Field and forage crops: how each is counted

Winter wheat is counted as grain at 3 t/ac with straw left; small-grain silage removes more (about 231 lb N, 79 lb P2O5 and 191 lb K2O at 22 t/ac, UC ANR Publication 9004), so enter those values for a forage rotation. Alfalfa removal at 10 t/ac hay is mostly fixed N. Perennial ryegrass and tall fescue are cut for hay at 6 t DM/ac, with P and K at NRCS book concentrations rather than the higher values measured on manured fields. Pasture is grazed: livestock return 85 to 95 percent of the nutrients they eat, so about a tenth of hay-equivalent removal leaves the field (University of Idaho CIS 392; low confidence). Crimson clover and vetch are cover crops terminated in place and remove nothing; enter hay removal if they are cut. Hops count the cones only, with vines returned.

CDFA FREP and UC Davis, California Crop Fertilization Guidelines

Removal per unit of harvested yield for silage corn, wheat, alfalfa (Meyer et al. 2007, UC ANR 8310), potato, almond (whole fruit: kernel, hull and shell; Brown et al. 2012), grapevine, avocado (Arpaia 1999), strawberry (Bottoms et al. 2013; Hartz), processing tomato (Geisseler et al. 2020; Hartz and Hanson 2009), lettuce (Johnstone et al. 2005), broccoli, carrot, cauliflower (Smith, Cahn and Hartz), melon (Hartz 2006) and onion (Biscaro et al. 2014). Yields for silage corn, wheat and alfalfa come from UC Cooperative Extension cost studies.

Geisseler (2016, updated 2025), Nitrogen concentrations in harvested plant parts

UC Davis literature overview of N removed per ton of harvested product; used for silage corn, alfalfa, potato, perennial ryegrass, tall fescue, cucumber, sweet corn and winter squash nitrogen.

USDA NRCS Agricultural Waste Management Field Handbook, chapter 6, table 6-6

Nutrient content of harvested crops; used for cabbage and table beets, for ryegrass and tall fescue P and K, and for the rule that removal counts only the harvested part (cover crops).

Oregon State University Extension

EM 9165 (vegetable cropping systems in western Oregon), EM 9154 (snap bean), EM 8585 (forage yields), FG 79 with PNW 513 (hops), PNW 780 with Strik and Bryla (2015) for blackberry and raspberry, Strik and Vance (2015) for blueberry, and the Oregon Vegetables asparagus page (from WSU FG-12). Heinrich, Smith and Cahn (2013) for spinach.

Other extension sources

Montana State University EB0210 (dry field peas, 40 bu/ac); University of Idaho CIS 392 (irrigated pasture); Michigan State University E2934 for Brussels sprouts and shelled peas, where no Western source was found (both marked low confidence on the crop).

USDA NASS

California yield per acre from the Vegetables and Noncitrus Fruits and Nuts annual summaries, used as the yield basis where the guideline does not state one.

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. For crops whose guide carries soil-test bands, the P and K readings place the field in the guide's soil-test band, and the crop card adds a row comparing the compost with that band's rate. The soil pool is not added to the compost: the band rate already credits it. Bands apply only when the lab used the guide's extract (Bray-P1 west of the Cascades, Olsen east, per OSU EC 1478; ammonium-acetate K); otherwise the medium rate stands. 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), Wallace Laboratories (El Segundo, 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.