I recall being taught that when an individual looses a limb or a body part, in this case an arm, the arm is to be buried in the ground for reasons of respect for the body that G-d has given. Is there a period of mourning, are certain prayers recited? I assume the keriah (tearing the garment) is not performed, is this accurate? Is the mourner’s kaddish said?
Only when there is a loss of life does one observe the customs of mourning; not upon the loss of a limb.
As you correctly stated, we bury a severed limb. One reason is, as you said, out of respect for our limbs. Another reason is because limbs can render a Kohain impure. Generally, one who is a Kohain may not come in contact with corpses, nor severed human limbs. The severed limb is buried to help the Kohain avoid contact with it.
Best Regards,
Rabbi Mordechai Dixler