Destroy all farms or not

According to experiments and documents referred to in this Tropico 3 thread on the official forums:

• Farms should be placed such that the area surrounding the building has the highest yield potential. Ideally, you place your farm on a spot with horrible yield but that has high yield around it to maximize use of farming land.
• Mines need to be placed on top of the deposit for peak efficiency.

Since there isn't much about the mechanics of the game that has changed between the Tropico 3 and 4, it's unlikely that Tropico 4 is any different. There are posts about Tropico 4 that say pretty much the same thing about farms, although they are on other non-official sites.

FWIW: My observations through my own playthrough in Tropico 4 supports the above statements. I don't have screenshots of overlays vs. crop placement or mine placement vs extraction rate, but the most productive mines for me have been right on top of the overlay area and the most productive farms were surrounded completely by green overlay areas with the road 3-5 squares away. They will build across the street to get to good land if they have to, but I usually place my road down a stretch of spread out farms for maximum effectiveness.

And now, SCIENCE! A ten-year experiment to determine whether bio farms are better than farms, for a particular crop. I chose Tobacco for this experiment, because I had to measure the Bio Farm via exports rather than just looking at its production directly.

The Method

Bio Farms show up at 1967, so I found a challenge that started in 1965, built a farm, and then built the bio farm when it showed up later. (The crop quality was uniform when I started this experiment; this image is from a few years in.)

I then set the wages to 1, made sure all of my citizens had a job, and imported a bunch of foreign experts. Then I raised the wages to 25 so none of them would look for a better job.

Most of the farmers were the same (below-average intelligence), but there was one ringer on the Farm that had Exceptional intelligence, and his final skill was completely maxed when the experiment ended, and another one with Good intelligence. None of the bio farm farmers had any better than Above Average intelligence. The results are therefore a bit biased, but hopefully still useful. The farmers with Below Average intelligence ended the experiment with about 55% skill. (The Ministry gave a 30% learning boost, and the Literacy Program gave another 30% learning boost.)

If you're curious, the other crop conditions for the bio farm: coffee was a pale green, corn was yellow, and sugar was orange. Tobacco, of course, was a deep green.

There were no problems with transportation during the experiment; the teamsters did their jobs.

The Results

The farm produced 6769 tobacco, and the bio farm produced 11578 goods. (This is, of course, horribly inaccurate; either number could be off by 500+ if I ran this experiment again.)

Over the course of the experiment, I exported a total of $203,836 in tobacco, and the price held steady at $1728 per 100 tobacco. That means that the farm was responsible for $116,968 of the exports, leaving the bio farm with the remainder of $86,868 in exports, or 5027 tobacco.

The farm produced 35% more tobacco than the bio farm, but it also had more skilled farmers. In all likelihood, the production of a bio farm is very close to the production of four farms producing different crops.

Also, a bio farm does not degrade the soil, but a normal farm does. I demolished the farms when I was done with the experiment, so you can see how the soil fertility for tobacco was degraded by the farm.

Given that the productivity is fairly similar, but the normal farm degrades the soil, I highly recommend bio farms as more productive over the long haul.

Summary

• The construction of a bio farm is about 3x that of a regular farm
• The upkeep + wages (when paying 5/month) is roughly equal to a regular farm (bio farm = 384/year, farm = 408/year)
• The productivity (across all goods) is 2x-4x higher at a bio farm (depending on whether you can find the perfect spot for all 4 crops; the Fertilize! edict will help here)
• Bio farms don't degrade the soil over time like regular farms do
• If you need 2 farms to feed a factory, you will need 2 bio farms to feed the same factory.