1. Introduction — You Cannot Fix What You Have Not Measured

Soil testing is the least glamorous and most valuable skill in growing. Every dollar spent on seed, transplants, irrigation, and amendments is a bet placed on the soil beneath them. Without a test, you are betting blind.

The problem is not that growers refuse to test. It is that most growers do not understand what the results mean, and so they either ignore them or follow generic recommendations that may not apply. A soil test is a diagnostic tool. It tells you what is present, what is missing, and what is blocking what is already there.

This article covers the full sequence: how soil works as a chemical system, how to collect a sample that actually represents your field, what each lab result means, and how to convert those numbers into a precise amendment plan. No guessing. No "add a little of this and see what happens."

The goal is soil that feeds plants efficiently, holds water, supports biological activity, and improves over time. That goal starts with measurement.

2. Soil Composition — What You Are Working With

Mineral Fractions

All mineral soil is composed of three particle sizes:

  • Sand (0.05–2.0 mm): Largest particles. Creates drainage and aeration. Holds almost no nutrients. Feels gritty.
  • Silt (0.002–0.05 mm): Mid-sized. Holds moderate moisture. Feels smooth, like flour.
  • Clay (<0.002 mm): Smallest particles. Enormous surface area. Holds water and nutrients through electrical charge. Feels sticky when wet.

The ratio of these three determines soil texture. The USDA soil texture triangle classifies soils into categories — sandy loam, silt loam, clay loam, silty clay, and so on. Texture is permanent. You cannot economically change it. You work with it.

A sandy loam drains fast, warms early in spring, and loses nutrients quickly. A clay loam holds water and nutrients but compacts easily, drains slowly, and stays cold longer. Neither is better. Each requires different management.

Organic Matter

Organic matter (OM) is the fraction derived from decomposed plant and animal residues. In most agricultural soils, OM ranges from 1–6%. Despite being a small fraction by weight, it controls a disproportionate share of soil function:

  • Nutrient holding: OM has a CEC of 150–300 meq/100g. Kaolinite clay, by comparison, has 2–5 meq/100g (Brady & Weil, 2017).
  • Water retention: Each 1% increase in OM holds roughly 20,000 additional gallons of water per acre (USDA-NRCS, 2013).
  • Biological habitat: OM is the primary food source for soil bacteria, fungi, and the organisms that cycle nutrients into plant-available forms.
  • Structure: OM binds mineral particles into aggregates, reducing compaction and improving root penetration.

Building OM is the single highest-leverage action in soil management. It improves every other metric.

Cation Exchange Capacity

CEC measures how many positively charged nutrient ions a soil can hold on its clay and organic matter surfaces. Units are milliequivalents per 100 grams (meq/100g).

CEC Range Soil Type Nutrient Holding
1–5 Sandy Very low — nutrients leach quickly
5–15 Loam Moderate — adequate with management
15–30 Clay loam Good — holds nutrients well
30+ Heavy clay or high-OM Excellent holding, but may drain poorly

CEC tells you the size of your soil's nutrient bank account. A high CEC soil can hold large reserves. A low CEC soil needs frequent, small applications because it cannot hold much at once. This number changes your entire fertilization strategy.

3. Sampling Technique — Garbage In, Garbage Out

A soil test is only as good as the sample. A single shovelful from one spot tells you about that spot. It tells you nothing about the field.

Protocol

  1. Divide the area into zones. Each zone should be uniform in soil type, drainage, crop history, and slope. A flat garden bed is one zone. A hillside with different drainage than the flat area is a separate zone.
  2. Collect 10–15 subsamples per zone. Walk a zigzag pattern across the zone. At each stop, push a soil probe or clean spade to the target depth and take a consistent core or slice.
  3. Depth: 6 inches for gardens, annual crops, and pasture. 8–12 inches for orchards and deep-rooted perennials. Use the same depth for every subsample.
  4. Combine subsamples in a clean plastic bucket. Break up clods. Mix thoroughly. Pull approximately one pint of the mixed soil into a labeled bag for the lab.
  5. Label each bag with zone name, date, depth, and any relevant history (last lime application, recent manure, etc.).

Timing

Test in fall for spring planting — this gives amendments time to react with the soil over winter. Lime needs 3–6 months to fully adjust pH. Testing in spring and applying lime the same week does almost nothing for that season's crop.

For established perennials and pastures, test every 2–3 years in the same season for comparable results.

Contamination to Avoid

  • Do not sample within 50 feet of a gravel road (lime dust skews pH), compost pile, manure storage, or building foundation.
  • Do not use galvanized or brass tools — they contaminate zinc and copper readings. Stainless steel or chrome-plated probes are standard.
  • Do not sample wet soil. Wait until it is moist but not saturated.
  • Do not mix zones. A sample that combines a sandy hilltop with a clay bottomland produces a result that describes neither.

4. Lab Tests Explained — What They Actually Measure

Choosing a Lab

Use a lab that runs Mehlich-3 extraction and reports base saturation percentages. Mehlich-3 is the most widely validated extraction method across soil types and pH ranges (Mehlich, 1984). Many state extension labs use this method. Private labs like Logan Labs, Midwest Laboratories, and A&L Laboratories are commonly used for detailed reports.

Expect to pay $15–35 for a standard fertility panel. Some labs offer add-ons for micronutrients, organic matter, and soluble salts.

What Each Test Measures

pH — Measures hydrogen ion concentration in soil solution on a scale of 1–14. Most crops grow best between 6.0–7.0. Below 5.5, aluminum becomes soluble and toxic to roots. Above 7.5, iron, zinc, and manganese become unavailable. pH is the master variable — it controls the availability of nearly everything else.

Buffer pH (SMP or Sikora) — Measures the soil's resistance to pH change. This is what determines lime application rate. Two soils can both read pH 5.5, but the one with higher CEC and more clay needs far more lime to reach 6.5. Buffer pH quantifies that resistance.

Organic Matter (%) — Measured by loss on ignition (burning off the organic fraction at 360°C) or Walkley-Black wet oxidation. Target: 3–5% for most crop systems. Below 2% indicates serious depletion.

Nitrogen — Soil nitrate (NO₃⁻) and sometimes ammonium (NH₄⁺). Nitrogen is mobile and changes rapidly, so a single snapshot has limited value. Many labs do not include it in standard panels for this reason. Nitrogen management relies more on crop demand calculations than soil test numbers.

Phosphorus (P) — Reported in ppm. Mehlich-3 values below 20 ppm are low for most vegetables. Above 50 ppm is sufficient to excessive. Phosphorus is immobile in soil — it stays where you put it. Over-application is a real problem. Excess P runs off into waterways and causes algal blooms.

Potassium (K) — Reported in ppm. Below 100 ppm is low for most crops. 150–250 ppm is adequate. Potassium is moderately mobile and should be monitored regularly.

Calcium (Ca) — The dominant cation in productive soils. Reported in ppm. Calcium controls soil structure — it causes clay particles to flocculate (clump into aggregates), improving drainage and root penetration.

Magnesium (Mg) — Essential for chlorophyll production. Reported in ppm. The Ca:Mg ratio matters more than absolute values in many systems.

Base Saturation — The percentage of CEC occupied by each base cation. This is where the Albrecht system (Section 5) becomes relevant. Reported as % Ca, % Mg, % K, % Na, and sometimes % H (acidity).

Micronutrients — Zinc (Zn), Manganese (Mn), Iron (Fe), Copper (Cu), Boron (B), and sometimes Sulfur (S). Reported in ppm. Deficiencies are common in alkaline soils (above pH 7.0) and in sandy soils with low OM.

CEC — Calculated from the sum of exchangeable cations or measured directly. Tells you the soil's total nutrient-holding capacity.

5. Reading Results — What the Numbers Mean

Two Schools of Thought

Sufficiency approach (university standard): If the nutrient level is above a critical threshold, no additional application is needed. Simple. Works well for field crops where the goal is preventing deficiency.

Albrecht/Kinsey approach (base saturation model): The ratio of base cations matters as much as their absolute levels. Ideal base saturation targets (Albrecht, 1975):

Cation Target % of CEC
Calcium 65–70%
Magnesium 12–15%
Potassium 3–5%
Sodium <3%
Hydrogen (acidity) 10–15%

The Albrecht approach argues that these ratios produce optimal soil physical structure — good aggregation, proper drainage, adequate aeration. When calcium is too low relative to magnesium, soils become tight and sticky. When magnesium is too high, the same thing happens.

Which to use: The sufficiency approach is well-supported by research for yield optimization in commodity crops. The Albrecht approach has strong observational support from practitioners managing soil structure, tilth, and biological activity. For small-scale growers, market gardeners, and anyone managing permanent beds, the base saturation model provides more actionable guidance on soil physical quality. Use both. Let sufficiency levels tell you if a nutrient is critically low. Let base saturation ratios guide your choice of amendment form.

Ideal Ranges by Crop Type

Parameter Vegetables Fruit Trees Pasture Herbs
pH 6.2–6.8 6.0–6.5 5.8–6.5 6.0–7.0
OM % 3–5 2–4 3–5 2–4
P (ppm) 30–60 25–50 15–30 20–40
K (ppm) 150–250 120–200 100–180 120–200
Ca (ppm) 1000–2000 800–1500 600–1200 800–1500
Mg (ppm) 150–300 100–250 80–200 100–250

These are starting points. Local conditions, specific cultivars, and crop load all modify the targets. The lab report usually includes recommendations. Cross-check them against these ranges.

6. pH Adjustment — The First Thing to Fix

pH controls nutrient availability more than any other single factor. Fixing pH before adding other amendments prevents waste. Applying phosphorus to soil at pH 5.0 is like pouring money into a locked safe — the phosphorus binds to aluminum and iron and becomes unavailable. At pH below 5.5, phosphorus availability drops by up to 70% (Havlin et al., 2014).

Raising pH (Acid Soils)

Agricultural limestone (calcitic lime) — Ground calcium carbonate (CaCO₃). The standard. Raises pH and supplies calcium. Effective neutralizing value (ENV) depends on particle size — finer grinds react faster. Look for 90%+ passing through a 60-mesh sieve. Reacts over 3–6 months.

Dolomitic limestone — Calcium-magnesium carbonate (CaMg(CO₃)₂). Raises pH and supplies both calcium and magnesium. Use when soil test shows magnesium is also low. Do not use if Mg is already adequate or high — excess magnesium tightens clay soils and reduces drainage.

Hydrated lime (Ca(OH)₂) — Reacts within weeks, not months. Highly caustic. Burns skin and plant tissue on contact. Use only when rapid pH correction is critical and plants are not present. Application rate is roughly half of ag lime for the same pH change because of its higher neutralizing value.

Wood ash — Contains calcium carbonate plus potassium. Effective but variable in composition. Test your ash if using it as a primary liming agent. Typical application: 5–10 lbs per 100 sq ft for light pH adjustment.

Application Rates

The buffer pH determines how much lime is needed. A general guide for calcitic ag lime to raise pH by 1.0 unit:

Soil Texture Lime Needed (lbs/1000 sq ft)
Sandy 25–35
Loam 50–75
Clay 75–100

These are approximations. Follow your lab's recommendation — they calculate rates based on your actual buffer pH.

Incorporate lime into the top 4–6 inches. Surface-applied lime without incorporation takes years to affect the root zone.

Lowering pH (Alkaline Soils)

Elemental sulfur (S⁰) — Soil bacteria oxidize sulfur to sulfuric acid, which reacts with carbonates to lower pH. Effective but slow — requires warm, biologically active soil. Application: 1–2 lbs per 100 sq ft to lower pH by 0.5–1.0 unit in loam soils. Takes 3–6 months.

Iron sulfate (FeSO₄) — Faster than elemental sulfur because it does not require biological oxidation. Also supplies iron. Application rate: approximately 5x the weight of elemental sulfur for the same pH effect. Useful for quick correction in small areas.

Acidifying fertilizers — Ammonium sulfate ((NH₄)₂SO₄) acidifies soil as a side effect of nitrification. Not a primary pH tool, but contributes over time.

Peat moss — Mildly acidifying (pH 3.5–4.5). Useful for blueberries and acid-loving plants at planting time, but impractical for field-scale correction.

Soils with free carbonates (calcareous soils) resist pH lowering. If your soil fizzes when you drip vinegar on it, sulfur applications will be partially neutralized. In these soils, growing in raised beds with imported acidic media may be more practical than fighting the native chemistry.

7. Macronutrient Amendment

Nitrogen (N)

Nitrogen drives vegetative growth more than any other nutrient. It is also the most mobile and the most easily lost — to leaching, volatilization, and denitrification.

Organic nitrogen sources:

  • Composted manure — 1–2% N. Slow release. Also adds OM, P, K, and micronutrients. Application: 1–2 inches incorporated before planting.
  • Blood meal — 12–13% N. Fast release for an organic source. Can burn if over-applied. Use as a targeted correction, not a primary source.
  • Feather meal — 12–15% N. Slow release. Requires microbial breakdown. Good season-long feed.
  • Fish meal — 10% N, 6% P. Moderate release. Also supplies phosphorus and trace minerals.
  • Legume cover crops — Fix atmospheric nitrogen through root nodule bacteria. Crimson clover fixes 70–150 lbs N/acre. Hairy vetch fixes 100–200 lbs N/acre. The most cost-effective nitrogen source for any grower with time to plan a rotation.

Synthetic nitrogen sources:

  • Urea (46-0-0) — Cheapest per unit N. Must be incorporated or watered in immediately — surface-applied urea loses 30–50% of its N as ammonia gas within 48 hours.
  • Ammonium sulfate (21-0-0-24S) — Supplies sulfur. Acidifies soil. Good for alkaline soils or sulfur-deficient conditions.
  • Calcium ammonium nitrate (27-0-0) — Does not volatilize like urea. Supplies calcium. More stable in surface application.

Timing: Split nitrogen applications reduce losses. Apply 30–40% at planting, 30–40% at peak growth (knee-high corn, fruit set in tomatoes), and the remainder based on crop appearance and expected yield.

Phosphorus (P)

Phosphorus is immobile. It stays in the top few inches of soil wherever you apply it. This means it must be incorporated, not broadcast on the surface.

  • Bone meal — 3% N, 15% P. Slow release. Works best in acid soils (below pH 7.0). In alkaline soils, phosphorus in bone meal becomes calcium phosphate and locks up.
  • Rock phosphate — 0-3-0 (available) but 20–30% total P. Extremely slow release — years, not weeks. Only effective in soils below pH 6.5 where acid dissolution makes it available.
  • Composted manure — 0.5–1.5% P. The best balanced source because it simultaneously builds OM.
  • Triple superphosphate (0-46-0) — Synthetic. Immediately available. Use when soil test P is critically low and the crop is already in the ground.

Caution: Do not apply phosphorus unless a soil test shows it is needed. Excess phosphorus is the primary nutrient pollutant in freshwater systems. Many established gardens have high P from years of manure and compost. Check the number before adding more.

Potassium (K)

Potassium regulates water pressure in plant cells, activates enzymes, and improves disease resistance. Deficiency shows as brown leaf margins, starting on older leaves.

  • Wood ash — 3–7% K plus calcium and trace minerals. Free if you heat with wood. Apply at 5–10 lbs per 100 sq ft. Raises pH — do not use on alkaline soils.
  • Greensand — 3–5% K. Extremely slow release. More useful as a long-term soil conditioner than an immediate potassium source.
  • Kelp meal — 1–2% K plus micronutrients and growth hormones. Expensive per unit K, but the trace mineral profile adds value.
  • Sulfate of potash (0-0-50) — Mined mineral (langbeinite). Supplies potassium without chloride. Preferred for sensitive crops — potatoes, tobacco, fruit.
  • Muriate of potash (0-0-60) — Potassium chloride. Cheapest per unit K. The chloride fraction can damage chloride-sensitive crops and soil biology at high rates.

Timing: Apply potassium in fall or early spring. It leaches less than nitrogen but more than phosphorus, especially in sandy soils.

8. Micronutrient Amendment — Small Quantities, Large Impact

Micronutrient deficiencies are common in:

  • Alkaline soils (pH > 7.0) — iron, zinc, and manganese become insoluble
  • Sandy soils — leached out over time
  • High-OM soils — some micronutrients bind tightly to organic matter
  • Soils with extreme pH in either direction

Key Micronutrients

Boron (B) — Essential for cell wall formation and pollination. Deficiency causes hollow stems in broccoli, internal cork in apples, and poor fruit set across species. The margin between deficiency and toxicity is narrow — 0.5 ppm is deficient, 5 ppm is toxic for many crops. Apply as borax (11% B) at 1–2 lbs per acre, not per bed. Over-application kills plants.

Zinc (Zn) — Required for auxin production and enzyme function. Deficiency causes stunted internodes, small leaves, and chlorosis between veins. Common in alkaline, sandy, and high-phosphorus soils. Apply as zinc sulfate (36% Zn) at 5–10 lbs per acre, or chelated zinc (EDTA or DTPA) for foliar spray at 1–2 lbs per 100 gallons.

Manganese (Mn) — Essential for photosynthesis and nitrogen metabolism. Deficiency mimics iron deficiency — interveinal chlorosis on young leaves. Common above pH 7.0. Apply as manganese sulfate (26–28% Mn) at 5–10 lbs per acre broadcast or 1–2 lbs per 100 gallons foliar.

Iron (Fe) — Required for chlorophyll synthesis. Deficiency shows as bright yellow new growth with green veins. Extremely common in alkaline soils. Soil-applied iron sulfate (20% Fe) is partially effective but often locks up quickly. Chelated iron (EDDHA chelate) stays available in soils up to pH 9.0 and is the standard for persistent correction. Foliar iron sulfate provides a fast temporary fix.

Copper (Cu) — Required for lignin production and reproductive development. Deficiency is less common but occurs in organic soils and high-pH conditions. Apply as copper sulfate at 3–5 lbs per acre. Use caution — copper accumulates in soil and can reach toxic levels with repeated applications.

Foliar Feeding

Foliar application bypasses soil chemistry entirely. The nutrient enters through the leaf cuticle and is available within hours. This is the correct approach when:

  • Soil pH makes the nutrient unavailable despite adequate levels
  • Deficiency symptoms are active and you need rapid correction
  • The nutrient is immobile in the plant (iron, manganese, zinc) and old deficiency damage will not repair

Apply foliar sprays early morning or late afternoon to avoid leaf burn. Use a surfactant (a drop of dish soap per gallon works) to improve leaf coverage. Spray to wet — not to drip. Foliar feeding is a rescue tool, not a replacement for soil correction.

9. Biological Amendments — Feeding the Soil, Not Just the Plant

Soil is not a container. It is an ecosystem. One teaspoon of healthy soil contains more microorganisms than there are people on earth. These organisms cycle nutrients, build soil structure, suppress disease, and create the chemical conditions that make minerals available to roots.

Compost

Finished compost (C:N ratio 15–20:1, earthy smell, no recognizable inputs) is the most complete biological amendment. It supplies:

  • Slow-release nutrients across the full spectrum
  • Organic matter that builds CEC and water-holding capacity
  • Diverse microbial populations including bacteria, fungi, protozoa, and nematodes
  • Humic and fulvic acids that chelate micronutrients and improve root uptake

Application: 1–2 inches incorporated into beds annually. For established perennials, topdress 0.5–1 inch as mulch.

Quality matters. Compost made from municipal green waste may contain herbicide residues (clopyralid, aminopyralid) that persist through composting and damage broadleaf crops. Source your inputs or test a bioassay — plant peas in a pot of the compost and watch for curled, distorted growth.

Compost Tea

Actively aerated compost tea (AACT) extracts and multiplies the microbial population from finished compost. The goal is to apply a diverse inoculum to soil or leaf surfaces.

Basic recipe: 5 gallons water, 1–2 cups finished compost in a mesh bag, 1 oz unsulfured molasses as microbial food, continuous aeration with an aquarium pump for 24–36 hours. Apply immediately — the microbial population crashes within hours after aeration stops.

AACT works best as a soil drench on depleted or recently disturbed soils. Evidence for foliar disease suppression is inconsistent in peer-reviewed literature, but many growers report practical results. Use it as a supplement, not a silver bullet.

Mycorrhizal Inoculants

Mycorrhizal fungi colonize plant roots and extend a network of hyphae far beyond the root zone, dramatically increasing the plant's access to phosphorus and water. In low-phosphorus soils, mycorrhizal colonization can increase phosphorus uptake by 20–80% (Smith & Read, 2008).

Two types matter:

  • Endomycorrhizae (arbuscular, AM) — Colonize most vegetables, grasses, herbs, and fruit trees. The type found in commercial inoculants.
  • Ectomycorrhizae — Colonize oaks, pines, birches, and other forest trees. Different product, different application.

Apply granular inoculant directly in the planting hole or furrow — hyphae must contact roots. Broadcasting on the soil surface is largely wasted. Do not apply high-phosphorus fertilizer at the same time — elevated soil P suppresses mycorrhizal colonization because the plant no longer needs the fungal partnership.

Brassicas (cabbage, broccoli, kale) and chenopods (beets, spinach) do not form mycorrhizal associations. Do not waste inoculant on them.

Cover Crops as Living Amendment

Cover crops are the most powerful biological amendment available. They build organic matter, fix nitrogen (legumes), break compaction (daikon radish, tillage radish), suppress weeds, feed soil biology, and prevent erosion.

Nitrogen-fixing covers (legumes):

  • Crimson clover — 70–150 lbs N/acre. Winter annual. Killed by mowing at full bloom.
  • Hairy vetch — 100–200 lbs N/acre. Aggressive. Excellent N contribution but hard to terminate without herbicide or tarping.
  • Austrian winter peas — 60–120 lbs N/acre. Cold-hardy. Easy to incorporate.

Carbon-building covers (grasses):

  • Cereal rye — Produces the most biomass of any winter cover. 4,000–8,000 lbs dry matter/acre. Suppress weeds through allelopathy. Terminate before heading to prevent reseeding.
  • Oats — Fast-growing fall cover. Winter-kills in zones 6 and colder, leaving a mulch mat for spring planting.

Multi-species mixes outperform monocultures. A mix of cereal rye, crimson clover, and daikon radish covers all functions: carbon, nitrogen, and compaction relief. The diverse root exudates support a wider range of soil organisms than any single species.

10. Building Soil Long-Term — The Multi-Year Strategy

Soil improvement is measured in years, not weeks. One season of cover cropping does not transform depleted ground. Five years of consistent practice does. The trajectory matters more than any single input.

Cover Crop Rotations

Design a rotation that alternates carbon-heavy and nitrogen-fixing covers:

  • Year 1 (fall): Cereal rye + crimson clover mix. Terminated in spring. The rye builds carbon. The clover fixes nitrogen.
  • Year 2 (fall): Oats + Austrian winter peas + daikon radish. The oats winter-kill, providing mulch. Peas fix nitrogen. Radish breaks compaction.
  • Year 3 (fall): Sorghum-sudan (summer) followed by cereal rye (fall). Massive root biomass from sorghum-sudan feeds deep soil biology.

Every cover crop rotation should include at least one legume for nitrogen and one grass for carbon. The carbon feeds fungi. The nitrogen feeds bacteria. Both are needed.

No-Till Transition

Tillage destroys soil structure, kills fungi, accelerates OM oxidation, and disrupts the pore network that moves water and air. Every pass with a rototiller sets back soil biology by weeks to months.

Transitioning to no-till or reduced tillage:

  1. Start with a thick cover crop terminated by mowing, crimping, or tarping — not plowing.
  2. Transplant through the mulch or direct-seed using a dibble or hoe to disturb only the planting spot.
  3. Accept slower decomposition in year one. The mulch mat will be thinner and less uniform than tilled-in residue. By year three, the soil biology catches up and surface decomposition accelerates.
  4. Manage slugs and voles — both thrive under mulch. Iron phosphate bait handles slugs. Habitat management (mowing borders, removing cover near beds in spring) reduces vole pressure.

No-till is not all-or-nothing. Reduced tillage — one shallow pass per year with a broadfork instead of a rototiller — captures most of the benefit while addressing real problems like compaction in heavy traffic areas.

Carbon Building

Soil carbon is the master resource. It drives CEC, water holding, structure, and biological activity. Building carbon requires more carbon entering the soil than leaving it. That means:

  • Maximize photosynthesis: Keep living roots in the ground as many days per year as possible. Every day of bare soil is a day of carbon loss.
  • Minimize oxidation: Reduce tillage. Tillage exposes soil carbon to oxygen and accelerates decomposition.
  • Add high-carbon inputs: Straw, wood chips (surface only — do not incorporate fresh wood chips), and grass-heavy cover crops all deposit carbon.
  • Maintain fungal networks: Fungi produce glomalin, a glycoprotein that binds soil aggregates and persists for decades. Tillage destroys fungal hyphae. No-till preserves them.

Cover crop biomass contributes 1,500–4,000 lbs of carbon per acre per year depending on species and termination timing (Poeplau & Don, 2015). Combined with compost additions and minimal tillage, it is possible to increase soil OM by 0.1–0.3% per year. That sounds small. Over a decade, it transforms soil.

Retest Every 2–3 Years

The cycle closes where it started: testing. Retest the same zones, at the same depth, in the same season. Compare results to your baseline. Are pH and base saturation moving toward targets? Is OM trending up? Have you created any new excesses?

Soil building is iterative. Test. Amend. Grow. Retest. Adjust. The growers who test consistently are the growers whose soil improves consistently. Everyone else is guessing.

11. Sources

  1. Albrecht, W.A. (1975). The Albrecht Papers. Acres U.S.A.
  2. Brady, N.C. & Weil, R.R. (2017). The Nature and Properties of Soils, 15th ed. Pearson.
  3. Havlin, J.L., Tisdale, S.L., Nelson, W.L., & Beaton, J.D. (2014). Soil Fertility and Fertilizers, 8th ed. Pearson.
  4. Mehlich, A. (1984). Mehlich 3 soil test extractant: a modification of Mehlich 2 extractant. Communications in Soil Science and Plant Analysis, 15(12), 1409–1416.
  5. Poeplau, C. & Don, A. (2015). Carbon sequestration in agricultural soils via cultivation of cover crops — a meta-analysis. Agriculture, Ecosystems & Environment, 200, 58–71.
  6. Smith, S.E. & Read, D.J. (2008). Mycorrhizal Symbiosis, 3rd ed. Academic Press.
  7. USDA-NRCS. (2013). Soil Health Key Points. United States Department of Agriculture, Natural Resources Conservation Service.
  8. Kinsey, N. & Walters, C. (2006). Hands-On Agronomy, 3rd ed. Acres U.S.A.
  9. Magdoff, F. & Van Es, H. (2009). Building Soils for Better Crops, 3rd ed. Sustainable Agriculture Research and Education (SARE).
  10. Weil, R.R. & Brady, N.C. (2016). Soil phosphorus and potassium. In The Nature and Properties of Soils, Chapter 14. Pearson.

Tags: [soil-science] [growing] [beginner]