This is sort of a difficult question to answer, because it is hard to define what a "Roman" accomplishment would be. For example, during the Roman period, we find the earliest evidence of things like horse collars and mouldoard ploughs in northwest Europe, but can this be said to be a Roman accomplishment? For one, they may have been prexisting but merely unevidenced, but more importantly, what does it mean for "the Romans" to have accomplished something? Someone within the empire, or specifically Roman citizens, or what?

Anyway, there were a variety of advances in agriculture that first appear or were first applied on a large scale during the Roman empire. A well known example are the complex watering systems of the Libyan valleys, which transformed what was before and is today into productive agricultural areas. These were so impressive that Gaddafi actually funded research into them to get ideas to expand modern Libyan agriculture. Of course complex watering systems long predated the Roman conquest of the region, but the developments of empire allowed these previously known techniques to be applied on a much larger scale.

There were also many developments of marketization. Along coastal Spain, for example, large parts of the farmland was transformed into what can only be described as a premodern version of agro-industry, producing olive oil, wine and garum (fish paste) on a massive scale for sale in the wider Mediterranean market. These complexes used technologies like water wheels in ways they had not been before. The Barbegal Mill complex in southern France is exceptional, but shows the upper end of what this use of technology could be.

So while it is difficult to say whether the Romans invented this or that, it is undeniable that the Roman period saw great changes in agriculture across thee empire.