Crit items: these are rare items that will pop up when you harvest a field. You are planting green onions well once in a while you will get green onion skins that scholars use to make green dye.
Crit soil: special soil used in the mastery skill to guarantee 100 well tended field which mean more fair bushels than poor bushels.

Once you fill up your xp box you will receive a title and another bar will open up next to it and your next tier becomes available to you. Now at this point you reach novice and are ready to keep going and fill the next box up and become a master apprentice farmer.( Note that even though your next tier is open up you cannot go past the novice box until the previous tier is completely master. Which you will know by the title you get LOTRO Gold and next to apprentice tab 2 yellow anvils will take the place of the xp bar.)

I suggest finishing one tier completely before moving into the next. Once you master a tier a tab on the bottom called mastery option becomes open, and this will let you use crit soil that will give you more fair bushels than poor when planting.

You keep doing this thru each tier once you have both anvils up on tier go to the next. When you get LOTRO Gold to artisian you will see that you need to go to an expert farmhand and use superior fields which are found north of hobbiton.

IV: supreme tier:

Now you have reached grand master farmer you want to go to the supreme tier. To get that to open up you need to do a quest from a quest giver. I found mine in michel delving near the expert cook vendor. The quest is easy the guy gives you a book you learn it and it is open up and bam there it is supreme skill opens up.

In conclusion I hope this basic guide helps you out in getting started in farming.
Link to Lotro forum.

Other links here: LOTRO Gold