Why use a fork and not a spade

The first reason for using a fork rather than a spade is that the strong tines penetrate problem soils easier than a spade could do.
On stony ground the fork breaks up the ground so that you can use a spade to dig it out. On clumping, clay soils you may be able to use the fork to both loosen and dig out the soil.
The second reason for using a fork rather than a spade is that the tines of the fork will cause less damage to root structures. Important when you are harvesting root vegetables as you want to loosen soil without damaging your crop.
Also, when transplanting, the fork will loosen the soil and allow you to get out more undamaged roots than you can with a spade. This will allow your plant to re-establish itself more quickly in the new position.
The last reason for using a fork rather than a spade is for weeding.
A fork will help you get out all the roots so they do not return.
How to choose a garden fork or spade
With so many garden tools on the market its daunting to choose a tool that is hopefully going to be with you all of your gardening life. So, here are the things to look out for Garden tools are put under a lot of pressure. So, it is important for them to be sturdy enough or they just will not do the job. If they are too light they will not last either and continue to do the job.
Tools with the blade/tines and shaft made of steel are always the best option. The shaft and handles are made from wood usually to keep the weight down. The tools would just be too heavy and lack the flexibility to use if the whole thing was constructed of steel.
– haxnicks.co.uk