COMPRESSION TESTING OF GRANULAR NPK FERTILIZERS

The crush strength of granular NPK fertilizer has been accurately dete rmined using Instron compression testing equipment. Stress-strain anal ysis shows a distinctive break point followed by break up of granule f ragments. The force required to crush the granules is a function of th e granule diameter but the calculated pressure required to crush each granule remained relatively constant. Factors such as moisture ingress and coating oils have been shown to affect granule strength. A direct link between caking of granular fertilizers and crush strength has be en established.