1) In order to be able to use a tractor on a field, one side of the field must be at least 30 squares. The overall number of hectares is irrelevant. A 30 x 10 will work, but a 25 x 12 will not, even though both have the same area.

1a) I later found that there is a slight change in the shade of green when drawing fields that also helps identify when it is able to handle tractors.

2) A 10 x 10 field will grow 2 fruit trees, but a 10 x 11 will grow 4.

2a) A 45 x 45 field will grow 48 fruit trees (even though it makes you buy 57 seedlings), which is the same number as a 50 x 50 field. Making it longer and narrower will not work, because if either dimension drops below 45, it loses a row.

3) The minimum field size of 0.01 hectares has 2 worker slots. Each additional 0.01 hectare adds another worker slot. So 3 worker slots for 0.02 hectares, 4 worker slots for 0.03, etc.

4) Get the Labor Law training right away for 500 at the farm house to give all of your workers 10% more endurance.

5) Add roads around fields or leave space to add them later, to reduce travel times for workers. If workers have to walk around two buildings or fields, rather than between them, the delay can be significant, especially since it's ongoing. - By Limmin.

5a) Roads have a a width of 2 field squares. Even knowing that though, adding roads in advance is recommended. - By Kaeru Gaman

6) Pressing the TAB key brings up a little display above each field/greenhouse with plant status. - By Army.

I have yet to try using the Forage Harvester, so I'm not sure if it works as a normal harvester or if it gets used after harvesting the crop.

Plows & Cultivators - Universal for all fields, not including greenhouses. Note that perennials do not need to have their field plowed and cultivated again after planting, but the yield will drop some. I've heard roughly 20%, but this may vary by crop.

Sprinker & Sprayer - The Sprinkler is universal for all fields, not including greenhouses. The Sprayer and Trailer With Water will not work in orchards due to their width hitting the trees.

Tractors - The Rega and the Etos are for any non-orchard field, and both work with every implement except the headers, which go on a combine (aka harvester). Orchards require the Orchard Tractor, but it can only pull the implements listed below for orchard crops. Note that the Rega and Etos can plant an orchard, but will not work on that field after the trees have been planted.

Orchard Crops - Orchard Planter, Orchard Sprayer, Box Trailer. The Trailer With Water and the Sprayer will not work (won't fit between the trees). Must be harvested by hand. Using a tractor with a trailer provides the workers with a dropoff point.

Potatoes - Potato Planter, Potato Digger (aka potato harvester). It would be nice if a Box Trailer could be used when harvesting by hand, but the game indicates that isn't an option.

Cabbage - Planter, Box Trailer. Must be harvested by hand.
Red Peppers - Planter, Box Trailer. Must be harvested by hand.
Raspberries - Planter, Box Trailer. Must be harvested by hand.
Strawberries - Planter, Box Trailer. Must be harvested by hand.
Tomatoes - Planter, Box Trailer. Must be harvested by hand.
Cucumbers - Precision Seeder, Box Trailer. Must be harvested by hand.
Pumpkins - Precision Seeder, Box Trailer. Must be harvested by hand.

Sunflowers - Precision Seeder, Rodon or Xena Combine (aka harvester) with corn reaper (aka header).

Corn (aka Maize) - Precision Seeder, Forage Harvester, Rodon or Xena Combine (aka harvester) with corn reaper (aka header).

Sorghum - Precision Seeder, Forage Harvester, Rodon or Xena Combine (aka harvester) with cereals reaper (aka header).

Lupine - Seed Drill, Rodon or Xena Combine (aka harvester) with cereals reaper (aka header).
Buckwheat - Seed Drill, Rodon or Xena Combine (aka harvester) with cereals reaper (aka header).
Colza (aka Rapeseed, Canola) - Seed Drill, Rodon or Xena Combine (aka harvester) with cereals reaper (aka header).
Oats - Seed Drill, Rodon or Xena Combine (aka harvester) with cereals reaper (aka header).
Wheat - Seed Drill, Rodon or Xena Combine (aka harvester) with cereals reaper (aka header).
Rye - Seed Drill, Rodon or Xena Combine (aka harvester) with cereals reaper (aka header).

Grass - Seed Drill, Mower, Windrower, Self-Loading Trailer (aka silage trailer).

This table is incomplete. Feel free to submit missing items in the comments, and I'll add them.