After some time I have been playing pak64 experimental in era of beginning 19th century.
I suggest some changes of paremeres of factories "old_farm" and "grain_farm" from food industry.
IDEA 1 - farm1.patch
One square kilometer of field yields 441 - 545 metric tonnes of wheat per year. (Data come from some statistic about recent agriculture in Central Europe. Not in English, so I do not link it.)
Square kilometer contains 16 fields in simutrans experimental. *
(* I use default settings: One tile is 250 meters --> 4 tiles is 1km ---> 4*4=16 tiles is one square km)
Dividing 441 by 12*16 yields 2.29t per tile. (There are 16 tiles per km2 and 12 month per year)
Using upper bound (545 t per km2 and year) leads to 2.83t per tile. Rounding previous results to natural numbers yields 2 or 3 t per tile in simutrans experimental.
So I suggest to use production_per_field=2 for old_farm and 3 for grain_farm.
(Using same algorithm for simutrans standard yields 27-34 t per tile.)
Another change deals with landscape. I suggest more fields. My suggestion is to multiply recent values of max_fields by roughly 2.5. It leads to similar amount output goods from fields as it had before the change.
More fields are desired in simutrans experimental according to the thread and I support the the idea:
http://forum.simutrans.com/index.php?topic=2472.0;I suggest not to increase min_field too much or not to increase at all as user should have possibility to remove some fields to be able to build a way to farm.
Farm fields very rarely spawn as probability_to_spawn is too low. I suggest to increases it at least 10 times. I changed it from 1 to 20. It playable.
There is a forest plantation in pak128 having forest fields with probability_to_spawn=75. It works nicely - fields spawn appropriately.
Both farms have small distribution_weight: 1 and 2. For example forest plantation (Nutzwald), iron ore mine and coal mine have distribution weight of 100. I suggest to multiple distribution weight by 10. 10 and 20 is still less than other factories have. On the other hand it is not too small (in contrast to value of 100).
IDEA 2 farm2.patch
Another idea: Lower a little bit productivity of factory (grain_farm, old_farm) and increase number of fields (max_fields). As wheat grown on fields, not in the farm building.
For example:
* old_farm:
Change of productivity from 80 to 60 give us 20 t of wheat, that acquired from fields. 2t of wheat per tile leads to increase of 10 wheat fields (max_fields).
P.S. These changes should not increase or decrease significantly total amount of wheat producted by farms.