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How to order and read a soil test report

A soil test report is usually one page and about thirty numbers, and half of what decides whether those numbers mean anything happens before the sample ever reaches the lab. This covers choosing a test, pulling a sample that represents the ground you're growing in, and reading every line the report hands back.

Updated September 2026 14 min read

Growing in a pot, not the ground?

This guide is about mineral soil (garden beds, lawns, fields), not a bagged potting mix, a peat or coco-based container blend, or anything tested by SME or PourThru. Those run on completely different units and extraction methods, so none of the ranges below apply to them. See how to test and read a soilless growing mix instead.

Which test to order

Every lab sells a base "routine fertility" package covering pH, organic matter, phosphorus, potassium, calcium and magnesium, usually with CEC and base saturation calculated from those. Buffer pH gets added automatically when the water pH comes back low enough that a lime rate matters. That base package is enough to run a straightforward garden or lawn program.

Beyond it, you're choosing add-ons:

Micronutrients (zinc, manganese, iron, copper, boron) if the crop is nutrient-hungry, the soil is sandy or high-pH, or a plant is showing a symptom pH and the macros don't explain.
Salinity and sodium (ECe, SAR) in arid or coastal regions, on soil irrigated with anything but rainwater, or in a greenhouse bed that's been fertigated for years.
Texture (a particle-size analysis) if you don't already know it by feel. Most labs estimate it from other numbers on the report if you skip this, which is a rougher guess.
Nitrate-N only close to planting. It moves through soil in weeks, so a reading from last fall says almost nothing about what's there now.

A cheap mail-in kit that reports only pH and NPK skipped CEC and base saturation, which means it skipped the numbers a lime or gypsum rate is sized from. Fine for "is this soil roughly in the ballpark," not enough to size an amendment plan with any confidence.

Extraction method

Labs pull phosphorus and the base cations out of the soil with different chemistry, Bray, Mehlich-3 or Olsen for P, ammonium acetate or Mehlich-3 for Ca/Mg/K. The numbers aren't directly comparable across methods, so two reports from different labs can legitimately disagree. If you're tracking a field or a bed over years, stay with one lab.

Pulling a sample that represents the ground

The lab can only analyze what's in the bag, and the single biggest source of error in the whole process is a sample that doesn't represent the area it's supposed to speak for.

Depth. About 6 to 8 inches for a tilled garden bed, row crop, or new lawn area. About 3 to 4 inches for an established, un-tilled lawn or pasture, since nutrients and pH stratify near the surface without tillage to mix them. Whatever you pick, sample every spot at the same depth, and keep it consistent year to year. Nutrient math on a report assumes roughly a 6.67-inch "furrow slice" of soil per acre by default; a shallower or deeper sample changes how much a given ppm reading represents.
Cores per sample. Pull 10 to 20 cores or slices from across the area and mix them into one composite bag. One core tells you about one spot; a soil test is only ever a picture of the whole area you composited it from.
Sample separately where the ground is different. A wet corner, an old animal pen, a spot near a foundation, a dead patch: composite those on their own if you want a real answer for that spot. Mixed into the main sample, they just blur the average without telling you anything about either area.
Avoid the obviously abnormal. Fence lines and gate areas (manure and traffic build up), old brush or ash piles, right next to a driveway (de-icing salt), and anywhere fertilized or limed in the last few weeks. Given time, apply fertilizer and lime after sampling, not before.
Clean tools. A stainless probe or a clean spade. A galvanized bucket can bias a zinc reading if zinc is one of the numbers you care about.

Timing

Sample when the soil is at field-moist, not waterlogged or bone dry, and at the same time of year each cycle if you're tracking a trend: pH and nutrient readings both drift a little across a season, and comparing a spring sample to last year's fall sample can look like a change that never happened.

pH and buffer pH

pH is the report's basic acidity reading, taken on a slurry of soil in water. Most vegetables and turf want somewhere in 6.0 to 7.0. Acid-loving plants (blueberry, azalea, most conifers) want it lower, down around 4.5 to 5.5. Below about 5.5, aluminum becomes soluble enough to injure roots in aluminum-sensitive crops, and phosphorus starts locking up. Above about 7.5, iron, manganese, zinc and phosphorus lock up from the other direction, which is why a high-pH soil can show micronutrient deficiencies even when the ppm numbers for those nutrients look adequate.

Most vegetables and turf 6.0 to 7.0

Acid-lovers (blueberry, azalea, conifer) 4.5 to 5.5

Scale 4.05.06.07.08.0 pH

Where a given reading sits relative to the target band matters more than the number alone. A pH of 6.4 reads as "close enough" for a vegetable bed and as "too high, add sulfur" for a blueberry planting.

Buffer pH is a different measurement answering a different question: not what the pH is, but how much it will resist a change. Two soils can both read pH 5.5 in water and need very different amounts of lime, because one has far more buffering capacity, usually tracking clay content and organic matter, than the other. The buffer pH test adds a buffer solution to the sample and reads the pH shift, which estimates the lime requirement directly rather than guessing at it from the water pH alone. Labs generally only run it when the water pH is low enough that a lime rate is in question; a near-neutral soil doesn't get one.

Without a buffer pH on the report, a lime rate falls back to CEC, and without CEC, to texture, each step a coarser estimate than the one before it.

Lime Calculator Turns your pH, and buffer pH or CEC when you have them, into an actual lime rate and product amount.

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Organic matter and CEC

Organic matter (% OM) drives water holding, nutrient holding, and biological activity more than any other single number on the report. Below about 2% is low: a soil that drains and dries fast and holds little in reserve. 3 to 5% is solid for most mineral soils. Above 6% is excellent, and worth noticing, since a mineral soil rarely gets there without years of compost or cover cropping behind it.

CEC (cation exchange capacity, in meq/100g) is how many negatively charged sites the soil has to hold onto positively charged nutrients, calcium, magnesium, potassium, against leaching. It's driven mostly by clay content and organic matter, and it correlates closely enough with texture that a texture reading is the fallback when CEC isn't on the report:

Sand 1 to 5 meq/100g Light and fast-moving. Small, frequent amendments; a big one leaches before it's used.

Loamy sand / sandy loam 3 to 12 meq/100g Still light. Most vegetable gardens and lawns on sandy ground land here.

Loam / silt loam 10 to 22 meq/100g The middle of the range, and where a lot of good garden and turf soil sits.

Clay loam / clay 18 to 50 meq/100g Heavily buffered. Takes more lime or amendment to move a point, and holds what's applied.

Typical CEC by texture. A sandy soil reading well above its range, or a clay reading well below, is worth a second look before sizing anything off it.

CEC and texture should roughly agree

Every lime, gypsum and nutrient build-up rate a soil calculator gives you is sized from CEC. A sand reading a CEC of 25, or a clay reading 4, is usually a keying error on the report or a different extraction method rather than an unusual soil, and it's worth a call to the lab before you act on it: everything downstream of that one number is wrong along with it.

Base saturation

Base saturation reports what percentage of the CEC's exchange sites are occupied by each base cation, calcium, magnesium, potassium, sodium, rather than by acidity. It's a second lens on the same Ca, Mg and K numbers already reported in ppm: two soils can carry identical ppm calcium and read completely different base saturation percentages, because the percentage is always relative to how much total exchange capacity the soil has to begin with.

Base sat Ca 60 to 70% Usually the majority of the exchange sites, by design.

Base sat Mg 10 to 20% Below this, magnesium can be genuinely short even with an adequate ppm reading.

Base sat K 2 to 5% A small share of the total, and easy to overshoot with heavy potash applications.

Base sat Na under 5% Above this, sodium starts working against soil structure. See salinity and sodium, below.

The Ca:Mg ratio (base saturation Ca divided by base saturation Mg) gets its own attention in some agronomy circles, the idea being that a specific ratio, not just each nutrient's own sufficiency, affects soil structure and nutrient uptake. Treat that claim skeptically: decades of trials have found crop yield essentially unaffected across an enormous range of ratios, and more than one land-grant extension service now says outright that the "ideal ratio" is unproven and not a sound basis for a lime or fertilizer decision on its own. A lab report that flags anything from about 2:1 to 7:1 as "balanced" is using a common convention, not a demonstrated requirement; each nutrient clearing its own sufficiency level in ppm, above, is the part backed by evidence.

The nutrient lines

Everything below is reported in ppm (parts per million), and each has a general sufficiency range: below the low end and a deficiency is plausible, above the high end and you're past the point where more does any good.

Phosphorus (P) 15 to 80 ppm Root establishment and early growth. Fixes tightly to soil particles and moves very little, which is why a P build-up takes so much more product per ppm than any other nutrient.

Potassium (K) 120 to 300 ppm Water regulation, disease resistance, fruit and tuber quality. Rarely shows an obvious visual symptom until it's already well short.

Calcium (Ca) 500 to 6,000 ppm Cell wall structure. Deficiency shows in new growth and in fruit (blossom end rot) rather than old leaves, since it barely moves once it's built into a cell.

Magnesium (Mg) 50 to 350 ppm The center of the chlorophyll molecule. Deficiency is a mobile-nutrient pattern: yellowing between the veins of the OLDER leaves first, as the plant moves it to new growth.

Sulfur (S) 10 to 60 ppm A building block of amino acids. Deficiency can look like nitrogen deficiency, but shows on NEW growth first rather than old, which is the tell between the two.

Zinc (Zn) 1.0 to 10 ppm Enzyme systems. Corn and pecan are the classic crops that come up short on it.

Manganese (Mn) 5 to 60 ppm Photosynthesis. More available in acid soils, and one more nutrient that locks up as pH climbs.

Iron (Fe) 4.5 to 120 ppm Chlorophyll synthesis. Classic interveinal yellowing on NEW growth, and the most common micronutrient deficiency on high-pH soils regardless of how much iron is there.

Copper (Cu) 0.3 to 6 ppm Enzyme systems. Shortfalls concentrate on sandy or high-organic-matter soils.

Boron (B) 0.5 to 3 ppm Cell wall formation and pollen tube growth. The narrowest gap between deficient and toxic of any nutrient here, so correct it in small steps.

Silicon (Si) 30 to 100 ppm Not classified as essential, but thickens cell walls and measurably helps drought, heat and disease tolerance, especially in grasses. No single standard extraction, so treat this one as a rough floor rather than a precise number.

General sufficiency ranges. Crop, growth stage and extraction method all shift these; a lab's own interpretive guide for your specific crop is worth checking against.

P and K are two different units, depending on what you're reading

The ppm reading on your report for phosphorus and potassium is always elemental P and K. But a fertilizer bag, and most build-up recommendations including this site's own, quote rates as P₂O₅ and K₂O, the oxide forms conventional in the fertilizer trade. They are not the same number: elemental P is about 44% of P₂O₅ by weight, and elemental K is about 83% of K₂O. Multiply P₂O₅ by 0.44 to get elemental P, or divide elemental P by 0.44 to get P₂O₅; the same math with 0.83 converts K₂O and elemental K. Comparing two recommendations without converting them to the same form first is the single easiest way to over- or under-apply by more than double.

Soil Amendment Calculator Enter every line from this section, set your own targets, and it prioritizes an amendment plan sized to how far short each nutrient is.

Open the calculator

Salinity and sodium

Not every report carries these lines; they matter most on irrigated ground in arid or coastal regions, and in a greenhouse or container bed that's been fertigated for years without much leaching.

ECe (electrical conductivity of a saturated paste extract, in dS/m) is the total dissolved salt concentration in the soil, all salts together, not sodium specifically. USDA Handbook 60 sets "saline" at an ECe of about 4 dS/m and up, the point where salt itself starts pulling water away from roots osmotically, regardless of which salts they are.

SAR (sodium adsorption ratio) measures sodium specifically, relative to the calcium and magnesium it's competing against in solution. A high SAR is what damages soil structure over time, since sodium disperses clay particles that calcium and magnesium would otherwise hold together. Handbook 60 calls a soil "sodic" at an SAR of about 13 and up, which corresponds to roughly 15% exchangeable sodium.

ESP (exchangeable sodium percentage) is the same idea measured on the exchange sites themselves rather than in solution, and it can come from two places on a report: directly, as the base saturation Na figure, or estimated from SAR by a standard regression. The two occasionally disagree by a few points; when both are on the report, the direct base saturation Na reading is the better one to act on.

The fix for high sodium is always the same shape: gypsum to swap calcium onto the exchange sites sodium was occupying, followed by enough irrigation to leach the displaced sodium below the root zone. Gypsum alone, without the leaching water behind it, mostly just sits there.

What to take away

A representative sample matters more than the lab: 10 to 20 cores composited per uniform area, a consistent depth, and the odd spots left out or sampled on their own.
pH says where you are. Buffer pH, or CEC as a fallback, says how much lime it takes to move it.
CEC should roughly match texture. When it doesn't, question the report before sizing a lime or amendment rate off it.
Base saturation is a second lens on the same Ca, Mg and K already on the report in ppm, weighted by how much exchange capacity the soil has to hold them.
P₂O₅ and K₂O are not the same units as the elemental P and K on your report. Convert (×0.44 and ×0.83) before comparing two recommendations.

Sources

General agronomic guidance, drawn from university extension services and one peer-reviewed review article. Extraction method, crop and region all shift the exact numbers on any real report, which is why this guide gives ranges rather than single cutoffs; a lab's own interpretive guide for your specific crop is the more precise word on any one of these.

University of New Hampshire Extension, "Soil pH and Plant Growth" ↗. Target pH ranges, and why nutrients lock up at both low and high pH.
University of Minnesota Extension, "Understanding Phosphorus in Minnesota Soils" ↗. Phosphorus binding to calcium above about pH 7.3.
University of Delaware Cooperative Extension, "A Comparison of Methods to Determine Lime Requirement" ↗. Buffer pH versus water pH, and why two soils at the same pH can need different amounts of lime.
University of Georgia Extension, "Cation Exchange Capacity and Base Saturation" (C1040) ↗. CEC by soil texture, and how base saturation is calculated from it.
Kopittke, P.M. and Menzies, N.W. (2007), "A Review of the Use of the Basic Cation Saturation Ratio and the 'Ideal' Soil," Soil Science Society of America Journal 71(2) ↗, and Iowa State University Extension, "Soil Calcium:Magnesium Ratios" ↗. The research case against treating a specific base saturation ratio as necessary on its own.
University of Connecticut Extension, "Watch Out for These Nutrient Deficiency Symptoms" ↗. Which nutrients move within the plant, and where a deficiency shows up first because of it.
South Dakota State University Extension, "Interpreting Soil Tests for Gardening" ↗, and University of Arkansas Extension, "Understanding the Numbers on Your Soil Test Report" (FSA-2118) ↗. General nutrient sufficiency ranges.
Ward Laboratories, "Fertilizer Knowledge: Understanding Fertilizer Forms" ↗. The P₂O₅-to-P and K₂O-to-K conversion factors.
University of Georgia Extension, "Soil Salinity Testing, Data Interpretation, and Recommendations" (C1019) ↗, citing USDA Agricultural Handbook 60. The ECe, SAR and ESP thresholds for saline and sodic soils.
University of Kentucky Cooperative Extension (Fayette County), "Soil Sampling" ↗. Sample depth by tillage, and how many cores to composite.
University of Maryland Extension, "Organic Matter and Soil Amendments" ↗. Organic matter percentage benchmarks.
University of Minnesota Extension, "Copper for Crop Production" ↗. Copper deficiency on sandy and high-organic-matter soils.

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