How can Spanning Tree be disabled on an individual port(s) of an AW+ switch without disabling Spanning Tree globally? There is no interface level command to turn the protocol off once it is is enabled within the global configuration. However, the transmission of Spanning Tree BPDU's from an individual port may be disabled:
interface port1.0.21
switchport
switchport mode access
switchport access vlan 50
spanning-tree portfast
spanning-tree portfast bpdu-filter enable
Make sure the Portfast is enabled, and that the port is placed in access (untagged) mode. Then, enabling bpdu-filter prevents the switch from sending BPDU's out that port, and also ignores BPDU's received. Even though Spanning Tree is enabled, it cannot "speak" the protocol if it cannot process BPDU's, which effectively disables it on an individual port.