One of the questions this past week regarding Roman technological innovation got me wondering how much of a role the almost limitless "free" labor (provided by the conquest slavery model) played in limiting Roman need for more complex agricultural machinery.
The comment by Pliny (I think?) showed a complete disinterest in the animal powered threshers. I know that in SE Asia a lot of agricultural work is still done by hand/animal power due to the cost benefit ratio not being favorable for small farmers, but in larger farms it's a necessity.
How did this not hold true for Romans, or was the lack of interest by the author just due to class snobbery?
I'll also accept detailed accounts of large scale Roman agricultural processes as an answer.
I think you have a few misconceptions here. One, Roman agriculture did not rely on free labor: slaves are a relatively expensive investment that must be maintained at constant cost regardless of the work requirements of the season (agriculture has a very variable work schedule) and so there is reason to believe that by the second century the experiments in large scale slave plantations had been abandoned. Certainly, it is quite hard to find real evidence of large scale slavery in the few agricultural areas (Egypt, parts or north africa, parts of central turkey) we have information. Pliny himself describes a tenant based system. I'm unaware of any unfavorable sentiments towards animal power.
Secondly, if anything late imperial agriculture was more sophisticated and more technological than earlier forms. There was seemingly greater efforts towards utilizing marginal lands in North Africa.
Archaeology and the Roman Economy is a good primer on the topic.