The water content of granular fertiliser has been measured satisfactorily using the absorption of a 10.688 GHz. microwave beam. The method used is shown to be simple, rapid, requiring relatively unskilled labour and suitable for fertiliser plant control purposes.
Apart from differences arising from temperature, age of product and particle size changes, the linear relationship between attenuation and water content is affected by chemical variation between granules. Experimentally the differences between selected compound fertilisers is sufficiently small for one composite calibration of attenuation vs. water content to apply to several materials.
The application of the microwave method to phosphoric acid, hydrated calcium sulphates, slurry intermediates and peat is also examined.