What are marcots / air layering
A marcot is a cutting that is grown directly on the branch of a  fruit tree that is already bearing fruit .The roots form on the tree itself and when they are big enough , the cutting is taken off the tree and is potted up and becomes an exact replica of the tree it came from.
Most marcots will produce fruit within 1 year but some fruit trees can take around 2 years to fruit.

What is the difference between a marcot and a grafted tree?

A Marcot is a lot easier to maintain than a grafted tree.

A grafted tree is made up of two parts (THE ROOT STOCK) which is the bottom part of the tree and the (SCION) which is the top part of the tree.The (SCION) is chosen from a tree that is already bearing fruit and is grafted on top of the (ROOT STOCK).The root stock is normally a tree that has been grown from seed.

This is why a grafted tree bears fruit quicker than a fruit tree grown from seed as the scion will flourish and will fruit sooner than a seedling, however it also means that the seedling part of the tree (THE ROOT STOCK) at the bottom of the graft will also keep growing and shooting out it's own banches.

If the (ROOT STOCK) part of the grafted tree isn't monitored and pruned back all the time it will steal energy from the (SCION) at the top of the graft and can also overtake the tree resulting in the (ROOT STOCK) seedling taking over and growing faster than the  (SCION).
As the (SCION) is the part of the tree that will bear fruit (NOT THE ROOT STOCK) you will then effectively be growing a seedling.

A Marcot is taken from a fruit tree that is already fruiting so it will also bear fruit quicker than a seedling just like a grafted tree. Some fruit tree marcots will actually fruit quicker than a grafted tree.

The difference between a marcot and a grafted tree is that a marcot does not need a (ROOT STOCK) or a (SCION) as it's roots are grown on the fruiting tree branch all by itself and is then taken off and grows as one part not two parts.

This means that a marcot will never need to be pruned back , unless you want to keep the tree short but it will have no competition  as there is no ROOT STOCK seedling at the bottom of the tree to compete with.This makes the tree easier to maintain without constantly having to prune the bottom branches like you would have to with a grafted tree.

Sometimes the leaves of the ROOT STOCK on a grafted tree can look the same as the leaves as the SCION so if the tree is left for a long time without maintaining it you may not even be able to tell the difference between what branches are from the ROOSTOCK or the SCION any more, and you may prune off lower branches that may actually be the part of the tree that you are not meant to cut off.(THE SCION)

Some fruit tree crops are only grown from Marcots such as Lychees and Rambutans so it goes to show that Marcots can be very successful and just will grow just as good as grafted trees.

Another reason Marcots can be better than grafted trees is that some ROOT STOCKS that are used for grafting are not compatible with all climates so if you live in a warmer climate and the ROOT STOCK is only suitable to cold climates or visa versa there is more of a chance that your fruit tree won't survive.

We have many marcotted trees growing on our property and they grow just as well as some of our grafted trees.A lot of the marcots actually grow better than their grafted counterparts as well.