Short answers, pulled from the story.
The three most important crops in ancient Rome were grains, olives, and grapes. Grain, especially durum wheat baked into bread, provided 70 to 80 percent of the calories in an average Roman diet. Olive oil supplied roughly 12 percent of calories and about 80 percent of necessary fats.
Egypt, northern Africa, and Sicily were the principal grain suppliers for Rome. Scholar Erdkamp estimated the city needed at least 150,000 tonnes of grain per year, calculated at 200 kg per resident annually. The process of supplying Rome with grain was known as the Cura Annonae.
Latifundia were large Roman estates exceeding 500 iugera (roughly 125 hectares) that used slave labor to produce crops at scale. They expanded significantly from around 200 BC as peasant farmers, drawn away by the Punic Wars, sold their land to wealthy buyers.
Slave labor was central to Roman agriculture, particularly on latifundia owned by the wealthy elite. Enslaved people performed planting, harvesting, and processing, while free men and citizens were hired to oversee them. This system enabled large-scale output but also contributed to economic inequality and, at times, slave rebellions.
Roman farmers used aqueducts for irrigation and built extensive water-powered mills; the facility at Barbegal near Arles used sixteen overshot water wheels and could produce an estimated 4.5 tonnes of flour per day. Farmers in northern Gaul used a grain-cutting machine called the vallus, pushed by oxen or horses, though it fell out of use after the 4th century AD.
The principal Roman agricultural writers were Cato the Elder, Columella, Marcus Terentius Varro, and Palladius. Pliny the Elder also covered agriculture extensively in books XII to XIX of his Naturalis Historia. A treatise attributed to Mago the Carthaginian, the Rusticatio, was an influential earlier work that is now lost.