Soil-Test Fertilizer Nutrient & Purchase Calculator

Compare prescribed N, P₂O₅ and K₂O with your planned product weights.
Deduct stock, calculate bags, leftovers and costs in KRW, then save your worksheet.

Defaults are fictional arithmetic examples, not recommended crop application rates.

Enter N, P₂O₅ and K₂O nutrient amounts from an existing prescription and planned product weights for the same field and stage. Do not enter soil-test ppm or prescribed product weights as nutrient amounts.

1. Area and prescribed nutrients

0.001–1,000,000

0–100,000

0–100,000

0–100,000

10a = 1,000 m². Keep basal and top-dressing stages separate. Whole-field kg values are not multiplied by area again.

2. Product analysis, planned use and purchase details

Use whole-field product weights in kg. Combine the same product and packaging into one row. Enter label mass percentages on an as-used basis. A price of 0 means not entered.

Product 1

0–100

0–100

0–100

0–1,000,000

0–1,000,000

0.001–10,000

0–10,000,000

Product 2

0–100

0–100

0–100

0–1,000,000

0–1,000,000

0.001–10,000

0–10,000,000

3. Nutrient comparison · 2,000 m²

N

Shortage 5 kg

Target nutrient
20 kg
Planned supply
15 kg
Coverage
75%

P₂O₅

Shortage 2.5 kg

Target nutrient
10 kg
Planned supply
7.5 kg
Coverage
75%

K₂O

Shortage 2.5 kg

Target nutrient
16 kg
Planned supply
13.5 kg
Coverage
84.375%

Review each nutrient separately. A numerical match does not establish application safety or mixing compatibility. Purchase surplus is excluded from planned nutrient supply.

4. Product purchase plan

6 bags · 100 kg

Planned use 87 kg · Purchase surplus 18 kg · Total remaining stock 18 kg

Total purchase cost: Enter missing prices

Subtotal for priced items: 0 KRW

Shipping excluded. Past stock costs are excluded from new purchases. Total bag count includes different bag sizes.

Product use, stock deduction, purchased bags, remaining weights and quoted costs
ProductUse kgStock used kgNet buy kgBag kgBagsOrdered kgSurplus kgStock left kgCost KRW
A75570204801010Enter missing prices
B120121022088Enter missing prices

Nutrients supplied by product

  • A: N 15 kg · P₂O₅ 7.5 kg · K₂O 7.5 kg
  • B: N 0 kg · P₂O₅ 0 kg · K₂O 6 kg

Sources checked: 2026-09-19 · Do not directly enter elemental P/K, soil ppm, liquid liters or dry-basis analyses. Confirm the application plan with a qualified agricultural adviser.

Turn an existing soil-test prescription into a purchase worksheet

This calculator compares prescribed nutrient amounts with the nutrients contained in product weights you plan to apply.
It scales the prescription to your field, adds the N, P₂O₅ and K₂O supplied by each product, and shows shortages and excesses separately.
It then deducts usable stock and rounds each purchase up to whole bags.

Fertilizers of equal weight can supply different amounts of nutrients.
Buying whole bags also does not mean that every purchased kilogram should be applied.
Keep the application plan and purchase plan separate to understand both nutrient differences and leftover material.
The tool does not diagnose soil, generate crop prescriptions or select products.
The mass calculations are general; this interface uses metric units and prices in KRW, with Korean RDA sources explaining the local prescription format.

Prepare the prescription and product labels

Prescription details

Check the field, crop, area, issue date and application stage.
Use the nutrient amounts for the particular basal or top-dressing application being planned.
A prescribed weight of a fertilizer product is different from the weight of its nutrients.
Ask the issuing adviser to clarify any ambiguous units before entering values.

Product details

Prepare the label analysis for N, P₂O₅ and K₂O, net weight per bag and current price quote.
Count only usable stock of that same product.
Different analyses or packaging need separate rows.
Combine planned uses of the same product and bag size into one row so bag rounding is not duplicated.

Understand N–P₂O₅–K₂O and product weight

Here, the three label numbers represent mass percentages of nitrogen N, phosphate expressed as P₂O₅ and potash expressed as K₂O.
A fictional 20-10-10 analysis corresponds to 20 kg N, 10 kg P₂O₅ and 10 kg K₂O per 100 kg of product.
Applying 75 kg of that product supplies 15 kg, 7.5 kg and 7.5 kg respectively on the label basis.
These amounts do not describe actual crop uptake, and the remaining product weight is not automatically useless material.

Values that cannot be entered directly

Elemental P and K are not the same values as P₂O₅ and K₂O.
Soil-test ppm or mg/kg describes a soil concentration, not kilograms of fertilizer nutrients to apply.
Dry-basis analysis may also differ from analysis on the as-used product mass.
The calculator does not convert liquid liters to kilograms using density.
Use verified mass values and matching nutrient conventions on both sides of the comparison.

Area conversion and nutrient targets

Target nutrient kg = prescribed kg/10a × field area in m² ÷ 1,000

10a = 1,000 m², and 1 ha = 10,000 m².
A 2,000 m² field equals 2 units of 10a, 0.2 ha or 605 pyeong.
The conversion uses 1 pyeong = 400/121 m².
The entered area must match the actual area covered by this application plan.

For a prescription in kg/ha, multiply by field area divided by 10,000.
For nutrient amounts already stated in kilograms for the entire field, choose whole-field kg.
That mode does not multiply the prescription by area again, so changing area alone leaves the target unchanged.
No crop-specific standard rates are loaded automatically.
All default values are fictional examples used to explain the arithmetic.

Calculate supply, shortages and excesses

Supply from each product

Nutrient supplied kg = planned product use kg × label percentage ÷ 100.
Add the contribution from every product for each nutrient separately.
Planned use is a product weight for the whole field, not a bag count or a rate per area.
Only combine products for the same field, prescription and application stage.

Independent comparisons

Shortage = max(target − supply, 0).
Excess = max(supply − target, 0).
An excess of nitrogen cannot cancel a shortage of phosphate.
Coverage = supply ÷ target × 100 when the target is positive.
A zero target has no coverage percentage; any positive supply is an excess.

A shortage or excess is a numerical difference from the entered prescription.
It is not an agronomic tolerance or a prediction of damage.
Even matching all three nutrients does not establish safety, timing, fertilizer-form suitability, salinity management or mixing compatibility.
No product is automatically recommended to fill a shortage.
Take the worksheet and labels to a qualified agricultural adviser before adjusting the actual application.

Deduct stock and round to whole bags

  1. Net purchase kg = max(planned use − usable stock, 0).
    If stock already covers the plan, no new bags are needed.
  2. Bags = ceil(net purchase kg ÷ bag weight kg).
    Calculate this separately for each product and packaging size before adding totals.
  3. Purchase surplus kg = ordered kg − net purchase kg.
    Remaining stock kg = original stock + ordered kg − planned use kg.

For 75 kg planned use, 5 kg existing stock and 20 kg bags, the net purchase is 70 kg.
Four bags provide 80 kg, leaving 10 kg after the planned application.
That leftover is caused by whole-bag purchasing and is excluded from nutrient supply.
Storage conditions and product condition must be checked before any future use of the remainder.

Step-by-step workflow and saved worksheet

  1. Choose one field and application stage, then enter its area and area unit.
    Area unit and prescription unit are separate controls.
  2. Select kg/10a, kg/ha or whole-field kg and enter the prescribed N, P₂O₅ and K₂O amounts.
    Do not deduct soil nutrients again if the prescription has already accounted for them.
  3. Add the name, three percentages, planned use, usable stock, bag weight and quoted price for each product.
    Up to ten products are supported.
    Combine identical products and packaging before entry.
  4. Calculate, review nutrient differences first, and then read the purchase plan.
    Editing inputs hides old results until you calculate again.
  5. Save the TXT worksheet containing input units, nutrient comparisons and product purchases.
    Add your prescription issue date and field or stage notes, then confirm the plan with an adviser and the order with the supplier.

Worked example with two fictional products

For a 2,000 m² field, assume a fictional prescription of N 10, P₂O₅ 5 and K₂O 8 kg/10a.
The whole-field targets are 20, 10 and 16 kg respectively.
These are arithmetic inputs, not official recommendations for any crop.

Product A: 20-10-10

Planned use is 75 kg, existing stock 5 kg and bag size 20 kg.
Supply is 15/7.5/7.5 kg of N/P₂O₅/K₂O.
The 70 kg net purchase requires four bags totaling 80 kg, leaving 10 kg.
At a fictional entered price of 25,000 KRW per bag, the purchase costs 100,000 KRW.

Product B: 0-0-50

Planned use is 12 kg with no stock and a 10 kg bag size.
Supply is 0/0/6 kg of N/P₂O₅/K₂O.
Two bags provide 20 kg, leaving 8 kg.
At a fictional price of 18,000 KRW per bag, the cost is 36,000 KRW.
Neither product names nor prices are market listings.

Combined result

Total supply is 15/7.5/13.5 kg, leaving shortages of 5/2.5/2.5 kg.
The order contains six bags and 100 kg, while planned use totals 87 kg.
Including the 5 kg of existing stock, 18 kg remains after use.
The two fictional quotes produce a total of 136,000 KRW.
Default prices are zero, meaning unknown, so the initial screen does not calculate a total cost.

Practical uses and cost interpretation

Before ordering from a supplier

Check the actual label and packaging to compare product bag counts and leftovers.
The total bag count may include different sizes; use ordered kilograms when considering transport weight.
Enter current quotes and budget shipping separately.

Using warehouse stock first

If stock covers planned use, that product has zero new purchase cost.
Its missing price does not prevent calculation of the total.
Otherwise, only the product-weight shortfall is rounded up to bags.
Remaining stock can inform the next purchase after checking its condition.

Checking quotes for a family member

A missing price for a needed purchase makes the full total unavailable.
Only the subtotal for priced items is shown, and it must not be treated as the final order cost.
Fill in missing quotes and recalculate.
Past stock costs and application labor are excluded from new purchase costs.

Frequently asked questions

Can I use only a crop name without a soil-test prescription?

No.
Supply an existing prescription.
The tool does not diagnose soil, generate rates, select products or optimize a blend.

Where do I enter a prescription stated as kilograms of urea?

Product kilograms differ from nitrogen kilograms.
The prescription fields require nutrient amounts for N, P₂O₅ and K₂O.
Ask the issuing adviser to clarify the nutrient basis if only product weights are listed.

What happens if a target is zero but supply is positive?

All supplied nutrient is shown as excess, and coverage has no ratio.
The calculator does not divide by zero or interpret a zero target as approval.

Can I ignore other nutrients while filling one shortage?

No.
Increasing one product can increase several nutrients.
Recheck every shortage and excess and discuss adjustments with an adviser.

Should I apply every purchased bag?

Purchase surplus is leftover material caused by packaging.
It is excluded from planned use and is not a recommendation for extra application.
Weigh out the amount confirmed for the actual plan.

Does organic fertilizer or compost have the same calculated effect?

Only label nutrient mass is compared.
Decomposition, mineralization, availability and uptake are not modeled.
Do not treat label nutrient kilograms as immediately plant-available nutrients.

Why enter area when the prescription is already whole-field kg?

Area records which field the plan covers.
Whole-field mode does not scale targets again.
If the area changes, verify whether the original prescription still applies.

Does a zero bag price mean free fertilizer?

No.
A zero price for a needed purchase means unknown and blocks the full total.
A product covered entirely by stock has zero new purchase cost.

Sources, verification date and checks before reuse

Sources were checked on 2026-09-19.
The RDA pages distinguish nutrient amounts from product quantities, and university extension guidance explains mass-percentage calculations.
No statutory Korean application rates or US regional crop recommendations are used as fixed inputs.
Recheck the prescription issue date, label basis, stock condition and supplier quote each time.

Input limits and decimal precision are software limits, not safe agronomic thresholds.
Displayed weights use up to six decimal places; bag counts use unrounded calculations.
Saved reports preserve inputs and calculated values so unit errors or missing products can be checked during consultation.

Review nutrient differences before placing an order

Enter your prescription and product details above, then save the worksheet.
Confirm shortages, excesses and the actual application plan with an agricultural adviser.
Confirm packaging and bag quantities with the supplier.
Keep separate worksheets for different fields or application stages and avoid counting the same stock twice.

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