|Mr. Swaminathan and bees. © 2011, The Hindu.|
Keeping bees, the obvious and most commonly considered physical inputs are nectar and pollen. The obvious outputs are honey and beeswax. This 'system' may also be considered in terms of energy (energetics) too, but that's another post. :-)
A less considered output, somewhat hidden from view is the 'manure' from the bees which is deposited in the vicinty of the hive. In the case of small scale beekeeping, that's in the garden. This article in 'The Hindu' suggests that 45-50kg of the stuff is produced per hive per year.
So, aside from the benefits of pollination on your plants, they are also being nourished from below!
All the more reason to keep bees, Naturally.