Currently you're only able to get a single Grade 3 Topsoil every hour. Getting Grade 2 and Grade 1 Topsoil is extremely slow as well -- I've bounced between nodes 300 times and only have 4 Grade 2 Topsoil to show for it.
Possible solutions:
-Remove the Rare tag on these items, so you can gather more than one per node.
-Make Grade 1 and 2 Topsoil appear more often.
Either of these would be great. There are barely any players selling Grade 1s and 2s, so I think a change to them is necessary at the very least.