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OFRA Fertilizer calibration tool shared

Calibrating fertilizer application to ensure uniform application at the desired rate is difficult.

The OFRA team has developed a tool for easy determination of the calibrated application for specific fertilizer type, rate and method of application. This a considerable help in producing fertilizer guidelines that are relevant to farmers,  rather than the conventional kilograms per hectare style of recommendations that are usually offered in extension material.

The tool can be accessed here

A farmer-friendly method of calibration is important for several reasons:

  • Farmers and others find it hard to estimate the area of a field
  • Once they have estimated an area of a field they find it hard to estimate how to apply the fertilizer at the right rate
  • People assume all fertilizer has the same density but there is a big variation such as 1.12 g/ml for single super phosphate to 2.22 g/ml for triple super phosphate.


Volume: First a farmer friendly measure is selected for use in fertilizer application – e.g. a bottle top, a matchbox, or another circular or rectangular container for which the volume is calculated from the dimensions.

Fertilizer type: Then a fertilizer type is selected from a drop down list this automatically provide the density of the fertilizer. Other fertilizer products can be added to keep the tool relevant.

Fertilizer rate:  Then a kg/acre or kg / hectare rate is selected

Method of application:  The method application is selected e.g. broadcast

Planting density:  The distance between rows and planting point are entered

The tool then gives a farmer-relevant suggestion for fertilizer placement to achieve the targeted rate. For example, using awater bottle lid that holds 5 g of urea, the calibration tool determines that band application of 40 kg/ha of DAP to maize planted with 75 cm row spacing, one lid is  sufficient for 2.1 m of band.

This calibration tool was developed by OFRA to enable accurate application of fertilizer. It can also be used for calibration of manure, compost or other input application. In phase 2 of the Africa Soil Health Consortium a series of tools will be developed, designed help make accurate and impactful ISFM support materials.

Professor Charles Wortmann, the lead scientist at OFRA, said:

“This is one of many tools we are and will be sharing to improve soil fertility management by smallholder farmers. This calibration tool is particularly useful for enabling farmers to accurately apply fertilizer, manure and other inputs.”

OFRA is a project jointly led by CABI and the University of Nebraska-Lincoln.