Fertiliser Calculator

Calculate nutrient content of a listed product based on kg/L applied

Calculate Kg/L of fertiliser to deliver required amount of nutrient from an existing product

Calculate nutrient content of a custom product based on kg/L applied

Calculate Kg/L of fertiliser to deliver required amount of nutrient from a custom product

Note: weight/weight for solids and weight/volume for liquids

Commercial crops usually require nutrients in addition to those found in the soil. Larger amounts of the macro-nutrients nitrogen (N), phosphorus (P), potassium (K), magnesium (Mg), calcium (Ca) and sulphur (S) are required compared with levels of micro-nutrients including zinc (Zn), iron (Fe), boron (B), manganese (Mn), molybdenum (Mo), copper (Cu) and chlorine (Cl).

Fertilisers containing macro- and/or micro-nutrients are applied to maximise economic yield of commercial crops. The amount of fertiliser applied, nutrient content and cost of fertiliser all contribute to the performance of the crop and may alter profitability.

Products in the Shed can be used in the crop planting tab to quickly create a fertiliser program based on the number of applications per crop (useful for broadacre and perennial crops) or, for vegetable crops, the number of applications per week based on a start/planting date and likely harvest date.

When the fertiliser entry has been completed and the Done button pressed, a summary showing the total amount of product applied, the nutrient content and the cost (weekly or for the whole season) is displayed.

Although DAFWA has tried to obtain and collate accurate and detailed information about fertilisers from different manufacturers, the information contained in a columns for micro-nutrients may be incomplete due to some manufacturers not disclosing the amount in their product. For more information see the Disclaimer tab.

Quick Calculator

• Click the Quick Calculator tab.
• Select the Brand from the drop down menu and then select a Product.
• Enter the Amount of product being applied in kilograms (kg) or tonnes (t) for solid or prilled (pelletised) fertiliser, or litres (L) for liquid fertiliser.
• Press Calculate for the nutrient content of the fertiliser applied.

For a custom product not in the list provided, enter the nutrient content from the label on the fertiliser bag or material safety data sheet (MSDS).

Some fertilisers display K as K₂O, P as P₂O₅, Ca as CaO and Mg as MgO. To convert these to the single elements K, P, Ca and Mg, multiply:

• K₂O x 0.830 = K
• P₂O₅ x 0.436 = P
• CaO x 0.715 = Ca
• MgO x 0.603 = Mg

Select the appropriate Amount in kilograms (kg) or tonnes, (t) for solid or prilled fertiliser or litres (L) for liquid fertiliser. Press Calculate for the nutrient content of the fertiliser applied.

There is no option to save calculations on the Quick Calculator. To save possible scenarios, apply for a login to use the full version of the Fertiliser Calculator.

Dashboard login

• New users will need to Create a user account in order to access the full version of the Fertiliser Calculator.
• After logging in, activate the fertiliser calculator by checking the Access fertiliser tool checkbox in your profile (only required for the first time).
• Once you have completed these steps you can access the full version including the Dashboard tab.
• When revisiting the Fertiliser Calculator please Login to access your previously entred data in the Dashboard tab

To add a fertiliser from the existing list:

• Select fertiliser to be added by pressing the edit button under the My Shed heading.
• To add a fertiliser from the existing list, select the Brand and then a Product.
• Enter your cost using the appropriate unit in kilograms (kg) or tonnes (t) for solid or prilled fertiliser, or litres (L) for liquid fertiliser.
• Press the Add button below brand in the top section of the page.

To add a non-listed fertiliser:

• Enter the Brand of the product.
• Enter the name of the product.
• Specify if it is a liquid or solid product by using the drop down menu under ‘Form’.
• Enter the details from the label or Material Safety Data Sheet (MSDS) of the nutrient content. Some fertilisers display K as K2O, P as P2O5, Ca as CaO and Mg as MgO.

To convert these to single elements K, P, Ca and Mg, multiply:

• K2O x 0.8302 = K
• P2O5 x 0.4364 = P
• CaO x 0.7147 = Ca
• MgO x 0.6031 = Mg

Enter your cost and a unit of that cost in kilograms (kg) or tonnes (t) for solid or prilled fertiliser, or litres (L) for liquid fertiliser.

You can account for the quantity of nitrogen from a water source by entering it as a custom product. Each mm of water applied equates to 1L per square metre. If your water contains 8mg/L N this will be 8kg of N per 100mm of water applied. See also link 'Applying nutrients to vegetables via irrigation' for more details on how to account for nitrogen in irrigation water.

To estimate the impact of nitrogen in water, add water as a custom product giving it a value for N in kg that is equal to the mg/L value from your water test.

For example, if your water contains 14mg/L, enter 14 into table. Estimate the irrigation used between normal fertiliser applications and enter the mm as L value and the rate (per) as hectares.

The contribution of N from water will be displayed in kg/ha.

To help make the Fertiliser Calculator more comprehensive for other farmers, tick the box Submit for approval before pressing the Add button below. By ticking Submit for approval, a notification will be sent to the site administrator requesting the new fertiliser be added to the system.

After pressing Submit for approval, you have the option to upload a picture of a fertiliser label so the reference can be checked prior to adding the fertiliser to the database. Select the location in which the picture is saved by pressing the Browse button and highlighting the file. Press the Upload button to load the photo to the system. Press the Submit button once again and the details will be sent to the system administrator.

Once the details are confirmed, the nutrient content of this fertiliser will appear in the product list for both the Quick Calculator and the full system. The price entered will not be included as this may be different for each user.

A list of products added appears at the bottom of the page. Once  you have finished adding products, press the Done button and the products will appear in the My Shed section.

Planting a crop

To make a fertiliser program, you must plant the crop as follows:

• Press the Add button under My Planting.
• Enter the Crop name identifier such as Block 1, Back paddock etc. and Crop type to be grown, for example, lettuce, wheat etc.
• Enter Planting Date, the expected Harvest Date or the number of days the crop will be growing and the other data box will auto-calculate. For perennial crops, tick the box marked Perennial which removes the planting and harvest dates but leaves the start and finish date of fertiliser applications.
• Enter the start and end date of the fertiliser applications.
• Enter the number of applications and frequency by selecting weekly or season.
• Enter the area of the crop and the units of the area entered to be able to calculate the program in a per area basis.
• Press the Add button and a schedule to add your fertiliser usage will be created.

Selecting products for a crop

The drop down menu of products is linked to Your Shed.

• Select a fertiliser to be added.
• Enter the amount of the fertiliser used and the appropriate unit (note that L is only available for liquid fertiliser).
• Specify the rate of the fertiliser applied by selecting square metre, acre or hectare.
• Press the Add button to save that fertiliser application (if you do not press add, the selection is not saved).

Once you have added a product into application one, you have the option to copy that product (at the same rate) to the next application or all applications via the Copy to next (↓ button) and Copy to all buttons.

If there is more than one application, you can use the Copy to previous (↑ button). This button appears from the second application. This function is useful if you have several of the same fertiliser applications each time. If you Copy to all, the information will appear in all applications. If you do not want the product you have copied to all in a particular application, delete it from that application by clicking the Remove tab.

Each application will open like a concertina as you press on the application number.

Once you have finished entering all the fertiliser applications, press Close to save the planting and View to save and see a summary of the information entered.

A summary of the total amount of product and the nutrient supplied by that product is shown for each application. At the bottom of the page is a summary for the full program entered. This can be used to compare the price of the product, the amount required and the nutrient content supplied by each product.

The amount for the area of the crop and the amount as a rate per hectare are displayed in the summary for each week and as a total for the planting.
In this view, you can print or download the fertiliser program for your records.

Fertigation is the practice of applying nutrients through irrigation water as it is being delivered to the crop. This is often used to supply a small amount of nutrient regularly to the crop, maintaining a more constant state in the soil. If irrigation is well controlled, fertigation can be an efficient and effective method of supplying fertilisers to crops.

Often different fertilisers are mixed together as a ‘stock’ solution providing the required nutrients in the correct ratios. Not all fertilisers are compatible mixed in water. They may precipitate and form sludge. The general rule is calcium should not be mixed with sulphates or phosphates. Table 1 shows a more comprehensive table of interactions.

A simple method to test the compatibility of fertilisers is to mix a small batch at the intended ratio in a container, stir and leave uncovered. If the fertilisers are incompatible, precipitate or sludge will form. Testing is recommended prior to mixing large batches or different fertilisers for the first time.

Fertilisers are not all equally soluble and solubility may change with the temperature of the water they are being mixed in and other nutrients in the solution. Table 2 shows the solubility of some common fertilisers.

Note: The table is a guide only. Fertiliser is generally less soluble at lower water temperatures and more soluble at higher temperatures. For actual solubility, contact the manufacturer for details.