No calculations yet
Nutrient Deficiency Diagnostic
Classify each nutrient as Very Low, Low, Optimal or High from soil test ppm values, using standard university extension critical thresholds.
Results
How to Use This Calculator
Enter each soil test nutrient in ppm (use your lab's extraction method — thresholds are approximate for Bray-1 / Mehlich-3). Click Calculate to see the rating for each nutrient and which ones need attention.
About This Tool
This diagnostic uses approximate university extension critical thresholds for mineral soils: N 20/40/80 ppm, P 10/20/30 ppm, K 75/120/160 ppm, Ca 500/1000/2000 ppm, Mg 50/100/200 ppm, Zn 1/2/5 ppm, Fe 10/20/40 ppm, Mn 5/10/20 ppm, B 0.3/0.5/1.0 ppm. Ratings are Very Low, Low, Optimal, High.
Applicability: Applicable globally, with particular relevance for North American and European cropping systems. Adapt rates to your soil test results.
How the Calculation Works
For each nutrient v: v < low = Very Low; low ≤ v < medium = Low; medium ≤ v < high = Optimal; v ≥ high = High. Thresholds reflect North-Central US extension values; your local lab's agronomist should interpret results for your region.
Real-World Example
N = 40 ppm (low-optimal boundary), P = 15 ppm (Low), K = 130 ppm (Optimal), Ca = 1500 ppm (Optimal), Mg = 150 ppm (Optimal), Zn = 2 ppm (Optimal), Fe = 20 ppm (Low), Mn = 10 ppm (Optimal), B = 0.5 ppm (Optimal). P and Fe need attention.
Common Mistakes & Tips
Common mistakes: ignoring that N in soil tests is a snapshot (not a recommendation), using one lab's thresholds on another lab's numbers, diagnosing by leaf color alone without soil or tissue tests, and applying micronutrients without confirming the critical deficiency. Always combine soil tests with tissue analysis.
Reviewed by Agricalc Editorial Team — Agricultural engineers and agronomists with 10+ years of field experience. Our team verifies every calculator formula against peer-reviewed extension publications. For site-specific advice, consult your local agronomist.
References
- USDA NRCS — Soil Health Assessment
- University of Minnesota Extension — Soil Management & Health
- FAO — Soils Portal
Frequently Asked Questions
How do I read soil test ppm values?
Each nutrient has a critical threshold: below it the nutrient limits yield; above it the nutrient is sufficient or excessive. Low = likely to limit yield; Optimal = meets crop needs; High = excess that may tie up other nutrients or leach.
What does zinc deficiency look like on corn?
Zinc deficiency shows as broad white bands on either side of the midrib on new leaves (the 'white bud' or 'striped' symptom), most common in high-pH, calcareous or cold wet soils. Soil test Zn below 1 ppm confirms the diagnosis. Apply 5–10 kg ZnSO₄/ha as starter.
Why is iron deficiency common in high-pH soils?
Iron is insoluble above pH 7.0 even when total soil Fe is high. Symptoms are interveinal chlorosis on new leaves. Correction: acidify soil with elemental sulfur, apply iron chelates (Fe-EDDHA) or improve drainage. Foliar Fe sprays give short-term relief.
Can soil test boron be too high?
Yes. Boron is required at 0.5–1.0 ppm in soil but becomes toxic above 2.0 ppm, especially to sensitive crops (beans, stone fruit, grapes). Excess B is common in arid soils or after repeated borax applications. Leaching with irrigation is the only correction.
Should I trust a soil test or a leaf test?
They answer different questions. Soil tests tell you what is in the soil; tissue tests tell you what the plant actually took up. When symptoms are unclear, take both at the same time. Tissue tests are especially useful for micronutrients, where soil thresholds are unreliable.
