Nutrient Roles & Deficiency Symptoms
| Nutrient | Class | Primary role(s) |
|---|---|---|
| Nitrogen (N) | Macro | Amino acids, proteins, chlorophyll, nucleic acids — drives vegetative growth |
| Phosphorus (P) | Macro | ATP/energy transfer, root development, DNA/RNA, flowering & seed set |
| Potassium (K) | Macro | Stomatal regulation, osmotic balance, enzyme activation, water-use efficiency |
| Calcium (Ca) | Macro (secondary) | Cell wall structure (middle lamella), membrane stability, signaling |
| Magnesium (Mg) | Macro (secondary) | Central atom of chlorophyll; enzyme cofactor for phosphorylation |
| Sulfur (S) | Macro (secondary) | Amino acids (cysteine, methionine), enzyme cofactors, oil synthesis |
| Iron (Fe) | Micro | Chlorophyll synthesis, electron transport (cytochromes), N fixation enzymes |
| Manganese (Mn) | Micro | Photosystem II water-splitting, enzyme activation, lignin synthesis |
| Zinc (Zn) | Micro | Auxin (growth hormone) synthesis, enzyme structure, internode elongation |
| Copper (Cu) | Micro | Lignin synthesis, electron transport, pollen viability |
| Boron (B) | Micro | Cell wall cross-linking, pollen tube growth, sugar transport |
| Molybdenum (Mo) | Micro | Nitrate reductase & nitrogenase — essential for N metabolism/fixation |
| Chlorine (Cl) | Micro | Osmotic regulation, photosystem II, disease resistance in some crops |
| Nickel (Ni) | Micro | Urease enzyme cofactor — required for urea nitrogen metabolism |
Mobility & Deficiency Symptom Location
Some nutrients can be resorbed from old tissue and shuttled to new growth when supply runs short (mobile); others, once deposited, stay put (immobile). This single property predicts where on the plant a deficiency symptom will first appear — a fast, practical diagnostic shortcut.
| Mobile (old leaves first) | Immobile (new growth first) |
|---|---|
| N, P, K, Mg, Mo, Cl | Ca, S, Fe, Mn, Zn, Cu, B |
S is a partial exception — technically somewhat mobile, but often behaves more like N in the field, so labs sometimes list it either way.
How Soil pH Controls Nutrient Availability
Soil pH doesn't add or remove nutrients directly — it changes their chemical form and solubility, which determines how much of each nutrient is actually dissolved in soil solution and accessible to roots. Drag the slider to see how the availability "window" shifts for each nutrient.
Nutrient Availability at This pH
Relative availability (0–100%) for each nutrient at the pH selected above — updates live with the slider.
Why this happens
| pH range | Mechanism |
|---|---|
| < 5.5 (strongly acidic) | Al³⁺ and Mn²⁺ dissolve into toxic concentrations; P binds tightly to Fe/Al oxides; Ca, Mg, K, Mo become scarce or leach easily. |
| 5.5 – 7.5 (near-neutral) | Widest availability window — most macro- and micronutrients are in soluble, plant-usable forms simultaneously. This is why ~6.0–7.0 is the general target for most crops. |
| > 7.5 (alkaline / calcareous) | Fe, Mn, Zn, Cu, and B precipitate as insoluble hydroxides/carbonates ("lime-induced chlorosis"); P re-precipitates with Ca; Mo availability actually increases. |
Nitrogen Form & the Rhizosphere pH Feedback Loop
The form of N a root absorbs changes the local (rhizosphere) pH — which then feeds back into the micro-scale nutrient availability right at the root surface, on top of the bulk-soil pH effects shown above.
NH₄⁺ (ammonium) uptake
Roots take in a positive ion, so they release H⁺ to balance charge → rhizosphere acidifies. Common with ammonium-based or urea fertilizers, especially in cooler/wetter soils where nitrification is slow.
NO₃⁻ (nitrate) uptake
Roots take in a negative ion, so they release OH⁻/HCO₃⁻ to balance charge → rhizosphere alkalinizes. Common in warm, well-aerated, biologically active soils where nitrification runs fast.
Soil Organic Matter, Carbon & C:N Ratio
Organic Carbon vs. Soil Organic Matter
Soil organic matter (SOM) is not pure carbon — it's a mix of carbon, hydrogen, oxygen, nitrogen and other elements bound into humus, roots, microbial biomass, and residues. Labs typically measure %OC (organic carbon) directly by combustion, then convert to %SOM using the van Bemmelen factor, since SOM is conventionally assumed to be ~58% carbon by weight (1 ÷ 0.58 ≈ 1.724).
Convert %OC ⇄ %SOM
Why it matters agronomically
Each 1% increase in SOM in the top 15 cm roughly corresponds to:
- ~1,000–1,200 liter ha⁻¹ additional water-holding capacity
- A slow-release reservoir of N, P, and S mineralized by microbial activity
- Better soil aggregation, infiltration, and resistance to compaction
Cation Exchange Capacity & Base Saturation
CEC is the soil's capacity to hold positively charged nutrients (Ca²⁺, Mg²⁺, K⁺, NH₄⁺) on negatively charged clay and organic matter surfaces — directly boosted by the organic matter discussed above — think of it as the soil's "nutrient bank account." Base saturation describes what fraction of that account is filled with base cations versus acidic H⁺/Al³⁺.
Rough estimate: clay ≈ 0.5–1.0 cmol/kg per %, montmorillonitic assumption; SOM ≈ 2 cmol/kg per % — illustrative only, texture/mineralogy vary widely.
| Cation | % of CEC | cmol(+)/kg |
|---|---|---|
| Ca²⁺ | — | — |
| Mg²⁺ | — | — |
| K⁺ | — | — |
| H⁺/Al³⁺ (acidity) | — | — |
C:N Ratio & Decomposition
Soil microbes need roughly 24 units of carbon for every 1 unit of nitrogen to build their own biomass. If the residue they're decomposing has a much wider ratio than that, they scavenge mineral N from the soil (immobilization) — temporarily competing with your crop. A narrower ratio releases surplus N into the soil (mineralization), feeding plants.
Blend calculator
Set the relative mass proportions of two organic inputs to see the resulting blended C:N ratio.
Result
Limiting Factors & Nutrient Interactions
Liebig's Law of the Minimum
Crop yield is capped by whichever essential nutrient is scarcest relative to demand — not by the average or sum of all nutrients supplied. Classically illustrated as a barrel: the shortest stave sets how much water (yield) the barrel can hold, no matter how tall the other staves are.
Adjust each nutrient's relative supply (0–100% of crop demand), or apply a crop's typical relative demand pattern below. The barrel fills only to the shortest stave.
Nutrient Interactions & Antagonism
Nutrients don't act in isolation — applying one in excess can physically or chemically block uptake of another, usually because they compete for the same root uptake transporters or exchange sites. Select a nutrient to see what it commonly antagonizes or synergizes with.
Deficiency Thresholds & Checker
Deficiency Threshold Reference Values
Deficiency is diagnosed against two kinds of measured numbers: a soil test critical level (below which a fertilizer response is expected) and a plant tissue sufficiency range (from lab analysis of a specific leaf position, usually the most recently matured leaf). Exact cutoffs vary by lab, extraction method, crop, and growth stage — the figures below are commonly cited general reference ranges for row/vegetable crops, not a substitute for a lab's own calibrated ranges.
| Nutrient | Soil test method | Soil deficient below | Soil sufficient range | Tissue deficient below | Tissue sufficient range |
|---|---|---|---|---|---|
| N | NO₃-N, 0–30 cm | 10 ppm | 15–40 ppm | 2.0% | 2.5–4.0% |
| P | Olsen (bicarbonate) | 8 ppm | 15–30 ppm | 0.15% | 0.20–0.50% |
| K | Ammonium acetate (exch.) | 60 ppm | 100–200 ppm | 1.0% | 1.5–3.0% |
| Ca | Ammonium acetate (exch.) | 400 ppm | 800–2000 ppm | 0.3% | 0.5–2.0% |
| Mg | Ammonium acetate (exch.) | 40 ppm | 60–150 ppm | 0.15% | 0.25–0.60% |
| S | Monocalcium phosphate (SO₄-S) | 5 ppm | 8–20 ppm | 0.10% | 0.15–0.30% |
| Fe | DTPA | 2.0 ppm | 2.5–10 ppm | 40 ppm | 50–150 ppm |
| Mn | DTPA | 1.0 ppm | 1.5–10 ppm | 15 ppm | 20–100 ppm |
| Zn | DTPA | 0.5 ppm | 0.8–2.5 ppm | 15 ppm | 20–50 ppm |
| Cu | DTPA | 0.2 ppm | 0.3–1.5 ppm | 4 ppm | 5–15 ppm |
| B | Hot-water extraction | 0.3 ppm | 0.5–2.0 ppm | 15 ppm | 20–60 ppm |
| Mo | Ammonium oxalate | 0.05 ppm | 0.1–0.3 ppm | 0.05 ppm | 0.1–1.0 ppm |
Check a value
Pick a nutrient and test type, enter a measured value, and see how it classifies against the reference ranges above.
Typical Crop Nutrient Requirements
Total nutrient uptake for a mature crop, from planting to harvest — use the crop selector at the top of the page to highlight one crop's profile below the comparison table. Values are illustrative order-of-magnitude figures for teaching, not a fertilizer recommendation — actual removal depends heavily on yield, cultivar, and region.
| Crop | N | P₂O₅ | K₂O | S | Ca | Mg | Yield basis |
|---|
All values kg/ha total uptake (nutrient removed in harvested biomass + residue).
Lab Report Analyzer & Recommendations
Enter values from a soil test or plant tissue analysis report and the tool will classify each nutrient against the reference ranges from the Deficiency Thresholds tab and generate general management recommendations. Leave any field blank if it wasn't measured. Select a crop from the dropdown at the top of the page first for crop-specific pH context.
Enter measured values
Classification
| Nutrient | Value | Status |
|---|