Welcome @EdC and @Angela! Great questions @sarge…
are the chemicals and fertilisers assets, inputs or materials?
Currently, farmOS has “Input logs” and “Materials”. Input logs are a type of log specifically intended for recording any kind of input that is applied to your areas or plantings. One of the fields on the Input log is “Materials”, which allows you to enter the names of materials that were used. This is primarily a “tagging” mechanism that makes it easier for you to find those logs again in the future by material name. But it is not a full-blown material inventory tracking feature.
In the future, the plan is to make Material into a new “Asset type” (on the same level as Plantings, Equipment, Animals, etc) - primarily so you can track your material inventory levels. So when you create an Input log, you’ll be able to optionally reference a Material asset and say “I used this much of that Material” (inventory adjustments).
That’s something we’re very close to This is one of the things to figure out: https://www.drupal.org/project/farm/issues/2916551
In the meantime, you can use a combination of the “Materials” and “Quantity Measurements” fields on Input logs. Quantity measurements are a place where you can store arbitrary weights/volumes/etc on the log. See https://farmos.org/guide/quantity/
Some are using this to store the actual quantities of materials that were applied in the input, and using the “Quantity Label” field to denote the material name (which is a bit redundant with the Materials field, and which the new Material asset inventory tracking will resolve).
Would we need to record the weather separately as an observation?
Some are putting this into the Notes field of the Input log. You can also create a separate Observation log to record the weather if you prefer. The Weather quick form creates observations of precipitation events, but could probably be made more general for field conditions more generally.