The Android design resources are a pretty good resource to look through.
If a frequent or important action within the context of that screen is to add a row then you should consider putting it in the main action bar. From the Android guide:
Show the most important actions of your app in the actions section. Actions that don't fit in the action bar are moved automatically to the action overflow.
Example action bar and list:
In this context your 'Add row' button is comparable to the New tweet button (if it is a main action)
The image below is an example of a contextual or overflow action menu (therefore at the bottom). The 'add' action is presented in the middle. Whether this is appropriate depends on context.
This is a similar pattern to what is being used frequently in iOS apps (see example below). Notice the emphasised main action.
A more unique approach has been employed by the Clear task app (see below). In this example the user pinches apart to create a new row. This works beautifully but is not that prevalent yet.
My final example is the Wunderlist andoid app. In my experience this works well. One thing that might impact this is whether you are adding a new row at the bottom or top.