The Contexts of Roman Society, part 5-2: Limitations on Agriculture
In histories of agriculture, a common character is the peasant, superstitious and stubborn and resistant to changes in practice and crops, who has to be tricked or coerced or even driven off the land entirely in order for progress to happen. This is an issue that arises from the historical perspective being predominantly elite-focused. Throughout history, it was elites who wrote histories to be read by other elites, and those elites rarely thought well of peasants or considered things from their point of view. The definition of elites could vary and broaden, but peasantries were rarely writers or readers of history, and so they were ill-represented, an issue that can continue in historiography today. The stereotype of the idiot country bumpkin still has a cultural resonance, even in post-peasant societies.
However peasants had reasons for their actions, and they were not stupid, at least no more than any broad subsection of society is moronic. Their parameters and mindsets varied substantially from those agricultural innovators and those who chronicled their efforts, but subsistence agriculture peasants were operating under a different paradigm.
Agricultural innovation did not come easily to smallholding peasants who operated on a subsistence agriculture system, for a variety of reasons. One was the nature of landholdings, split up into a variety of patches across the village lands. As mentioned, this was done for reasons of food security, but made economies of scale impossible for nearly all landowners. Given that restriction, many farmers wouldn’t make the effort, particularly if there wasn’t a convenient market that could take the surplus.
With many peasants all holding small strips next to each other (long narrow strips were the preferred format because of the ease of plowing), fencing individual strips was not feasible. It took up space, which could be proportionally quite large compared to the strips, and used up timber that could be used for other things. Also animal manure was the only fertilizer they had, so the livestock were let out to graze on the stubble and fertilize the fields with their droppings, which they couldn’t do if there were a bunch of fences in the way. (There was also an element of peasant egalitarianism at work here. A richer peasant may own more livestock, but while grazing their droppings would help fertilize the strips of other poorer peasants.)
However this meant that everyone needed to coordinate his crop routines, so that the livestock would be let out to graze just on stubble. Different crops were planted and harvested at different times, and it was no good to try a different crop if that meant the village livestock would come eat it because everyone else was at stubble and wanted to manure but the innovator’s wasn’t ready to harvest yet. With the need for consensus, it was much easier to just follow the path of traditional inertia and just do things the way things were always done.
But it wasn’t just inertia. The way things were always done had clearly worked, as evidenced by the fact that the village and peasants were there. The old ways didn’t always work, as peasants painfully knew, but they had a backup in the village, with neighbors helping those having bad years with the understanding that they would be helped in turn. (Disasters can hit that strike the whole village, but most calamities are more localized and random. Frost can kill the crop in one part of the village, but a more sheltered area is fine, for example.)
But, for the sake of argument, the village does decide to try something new. Except they don’t have the advantage of hindsight, and that something new may fail. And if that happens, the peasants have no backup. Everyone had to try the new technique or crop, meaning that in the event of failure, it could very well be universal, meaning that there are no peasants who had good years who can provide back up. This is where the inevitable setups can and frequently do turn into disaster, because it breaks the only social safety net.
An agricultural innovation that fails can easily mean that a peasant has to watch some of his or her children starve, and if some must be sacrificed it must be the youngest. The next crop needs to be planted and harvested, and so if there is not enough food to go around in the winter, those who can work in the spring must be prioritized, and those who cannot are sacrificed for the greater good. The old ways have their risks and chances of failure, but they at least have a track record, a critical consideration when the costs of failure can be so high.
The Roman heartland, like the rest of the Mediterranean, was poorly endowed agriculturally compared to lands north of the Alps. Soils were thin and the vast majority of the heartland was hilly or mountainous, and so much of the landscape was not the ideal farming type. Roman farmers did what they could, but their means were limited and the hand they had been dealt was a poor one, especially compared to the likes of their French or German contemporaries. Travelers who had been on both sides of the Alps noted the smallness of Mediterranean livestock compared to those north, with adult sheep being described as small enough that an adult man could lift them in one hand. 
The Mediterranean consumer did have a different advantage over his or her northern contemporary, in that they had a greater variety of plants available to them such as fruits, vegetables, and herbs. The Romans sometimes called scurvy the Dutch disease. Because of their fairly short ocean voyages to India via the Red Sea, scurvy was much less of a danger for them compared to the Latins, and so scurvy wasn’t associated with long sea voyages. But Greek mercenaries were common in Lotharingian army units, and in winter garrisons the scurvy had been a serious danger, unlike at home where citrus was bountiful, dried if need be, but always present.  (One side effect was to obscure the cause of scurvy, with many attributing it to bad air from cold northern winters or too much close confinement on a long sea voyage, as opposed to a nutritional deficiency.)
But producing those varieties in quantity was hard, with thin soils and marginal landscapes that did not yield much, especially when manure was the only fertilizer, and there never seemed to be enough of it. As the city night soil fertilized the fields outside the city, peasants used their household night soil to fertilize their gardens. Animals were used for a variety of products and labor, but their manure was very important. Many peasants kept pigeons, which were a very cheap source of protein and easy to keep in large numbers, but the primary purpose of pigeon keeping was for their droppings, excellent fertilizer by the standards of the day. 
The necessity of manure to make marginal lands productive did impose a vicious feedback loop. Those on marginal lands would be poorer because of low or nonexistent surpluses, which meant they couldn’t have as many farm animals. That deprived them of the all-important manure needed to make their lands viable, which meant they would stay poor. With a lack of fertilizer, marginal lands had to be fallowed for much of the time, sometimes producing only 1 crop every three years, or worse. Thus poorer peasants were especially dependent on the communal pasturing of village livestock on the stubble, enforcing the need for everything to follow the same crop pattern. The other source of manure, working with local pastoralists, also imposed the same need to prevent enclosures and synchronize crops.
This also had an effect on richer peasants who might have enough land holdings, if consolidated, to make a serious effort at commercial agriculture. If they did so, they would also be consolidating their livestock and their vital manure, which would significantly weaken the viability of their poorer neighbors’ lands. And those poorer neighbors knew it and thus would resist any such effort. And while the richer peasants might, by virtue of their comparative wealth, get away with it in the short-term, such success would likely turn to ash in the long-term. The consolidation would increase the risk of one disaster wiping out all the rich peasant’s crop at once, and there were few peasants, even the richer ones, who could readily absorb such blows without recourse to the village support network. Except by their previous actions, they had both alienated the neighbors who would provide such support, and weakened their ability to provide said support even if they had been inclined.
Thus the old ways of doing things had tremendous staying power. It has been said that in terms of material products and practices, the peasants of Phrygia who’d watched Odysseus march off to war with the Persians would’ve been little different from those peasants of Phrygia who’d watched Croesus march off to war with the Persians some twenty one centuries earlier. There is much truth to this statement, provided one is using examples from rural areas distant from markets and towns. There were many more of those markets and towns in 1640 CE compared to 640 BCE, but outside that zone the statement has merit.
Probably the most famous example of this traditionalism, at least in Latin accounts of Roman social life, though is unfair and betrays an equally traditional custom of judging peasantry by non-peasant contexts. Water wheels were extremely common in the countryside in the 1640s, used for a variety of tasks. But most were horizontal water wheels, of a type Strabo would’ve recognized, and far less efficient than the vertical water wheel. At first glance this seems like a textbook example of the primitive nature of much Roman agriculture.
However these horizontal water wheels, while inefficient, are easy to build and maintain. Vertical water wheels are far more efficient in terms of the work they can do but require a complex gearing mechanism to make that work useful, and are thus far more expensive. A great landlord with the ability to force their peasantry to use only their mill thus had a large captive audience of customers that would merit the expense to pay for the greater initial outlay. But the horizontal water wheels of the countryside were primarily for the use of individual or small group peasant holdings. There was not enough expected advantage to warrant the expensive vertical water wheel, but the horizontal fulfilled their needs admirably, and so that is what they used and continued to use. It should also be noted that in contexts where the scale was big enough to justify the extra expense, vertical water wheels would be found in abundance.
Thus those many horizontal water wheels are a good exemplar, but for different reasons than are usually assumed. The peasants who built and maintained them knew their needs, and also their resources and limitations, and the limits of the possible and the dangers of pushing past them, off a cliff, were ever present in their minds. But the water wheels also showed a willingness to develop and innovate when the opportunities were present and available. Ever since the end of the Time of the Troubles and the era of the Flowering, through the rising urbanization and commercialization of society, those opportunities, for both good and ill, had been growing.
 From OTL, see Braudel, Mediterranean, Vol. 1. Early modern livestock in general would be small compared to modern varieties, but the difference in size was present and noticed by observers in the OTL 1500s and 1600s.
 Also from OTL, but replace Romans with Spaniards. Spanish garrisons in the Low Countries contracted scurvy, which they were not used to getting when stationed in Iberia or Italy.
 Michael Decker, “Frontier Settlement and Economy in the Byzantine East” in Dumbarton Oaks Papers 61 (2007), pgs. 258-60.