How is nitrogen fertilizer requirement calculated?

N requirement (kg/ha) = Yield goal × N removal per unit yield − (Soil test N × soil factor) − Organic matter credit. For corn: ≈20 kg N per tonne grain yield minus soil N credits.

What do soil test P levels mean?

For Mehlich-3 extraction: Low ( 50 ppm): no fertilizer needed. Luxury range (>75 ppm): potential water quality concern.

What is the cation exchange capacity (CEC) and why does it matter?

CEC (cmol/kg) = total negatively charged sites holding cations. High CEC soils (>20): better nutrient retention, buffer more fertilizer. Sandy soils: CEC 2–5. Clay/organic soils: CEC 20–60+.

Soil Nutrient Balance Calculator — N, P, K Analysis

Calculate soil nitrogen, phosphorus, and potassium balance from soil test results, yield goals, and crop removal rates.

Tap constants to insert

Physical Constants Reference

Constant	Symbol	Value	Units
Speed of light	c	2.99792458×10⁸	m/s
Planck's constant	h	6.62607015×10⁻³‴	J·s
Boltzmann constant	kʙ	1.380649×10⁻²³	J/K
Avogadro's number	Nₐ	6.02214076×10²³	mol⁻¹
Gravitational constant	G	6.6743×10⁻¹¹	N·m²/kg²
Gas constant	R	8.31446	J/(mol·K)
Elementary charge	e	1.602176634×10⁻¹⁹	C
Electron mass	mₑ	9.1093837015×10⁻³¹	kg
Proton mass	mₚ	1.67262192369×10⁻²⁷	kg
Fine-structure constant	α	7.2973525693×10⁻³	dimensionless

How to use this calculator

1
Enter the required values
Enter the required values into the Soil Nutrient Balance Calculator — N, P, K Analysis input fields.
2
Adjust settings
Adjust any settings, select applicable options, or choose units as needed.
3
Calculate the result
Press Calculate to compute the result using the underlying formula.
4
Interpret the output
Review and interpret your result using the provided context, reference ranges, or explanatory notes.

Formula

Result = f(physical quantities, constants, conditions)

physical quantities: Measured values with units entered into the Soil Nutrient Balance.
constants: Physical or chemical constants (e.g. CODATA values, gas constant, Avogadro's number).
conditions: Temperature, pressure, concentration, or environmental state of the system.
Result: Computed physical or chemical quantity with associated units.

Compare results with standard reference values or published experimental data.

Glossary and Definitions

Physical quantity: A measurable property of a physical system, expressed as a numeric value with units.
Constant: A fixed, well-defined value (e.g. a CODATA constant) used across scientific calculations.
Significant figures: The digits in a measurement that carry meaning, reflecting the precision of the instrument.
Reference value: A published standard or experimental value used to validate a calculated result.
Soil nutrient calculator: A key concept referenced by the Soil Nutrient Balance: Calculate soil nitrogen, phosphorus, and potassium balance from soil test results, yield goals, and crop removal rates.
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Soil test calculator: A key concept referenced by the Soil Nutrient Balance: Calculate soil nitrogen, phosphorus, and potassium balance from soil test results, yield goals, and crop removal rates.

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