Since we do not possess any reliable information which points us towards the hypothesis that agriculture before the XIX and XX centuries made use of synthetic fertilizers and other sorts of treatments for crops, the main difference between dietary staples such as wheat or rice from farmland of around XV century northern Italy would have most likely been the lack of chemically produced treatments (chemical here is to be read as a product of chemical industry, not in the process inherent of its function).

We can speculate what could might have been involved in food production as long as protection from harmful organisms (namely bugs or bacterial/fungal infestations which I shall define with the umbrella term "blight") by reverse-thinking the traditional methods still employed, in some rural areas of Europe, as late as the 1970s. Ladybugs might have been employed to counter aphids damaging crops just like small numbers of common rose flowers could be planted close by grapevines in order to check the vineyard's health since many parasites of grapes also afflict common roses.

Surely fertilizers would have been restricted mostly to animal manure, often linked to the two-year or three-year rotation of crops and grazing alongside the planting of several different types of grains or legumes in order to stem, where possible, the damage caused by a sudden blight or bad harvest of a given staple. Documents from the Hospital of Holy Mary of our Annunciation of Capua from 1477 state that the lands which the Hospital rented to farmers were growing three to four variants of wheat grains, mostly divided into types which would mature at different times throughout the year (indicative of this is one name "March grain", a strain which could be harvested already in March, whereas in southern Italy the usual period for crop yield would be around June or July). Rotation of crops would also provide a modest recuperation of nutrients and enzymes within the soil thanks to the nitrogen-fixating interaction between bean family plants and the soil bacteria Rhizobium leguminosarum. We can safely assume that this mechanism was not known in detail but already understood in the Middle Ages and Early Modern Age.

Animals would also have been fed with much of the same crops and forage we have discussed above. Even though there were some additions made to cattle food (one example is the addition of a flower naturally growing close to patches of soil present in the northern region of nowdays Campania, in Italy, partly corresponding to the Roman area named Campania Felix, which would partly be submerged during heavy rains, and would be connected to an increased milk production linked to the traditional dairy production of the region), there wouldn't have been anything close to modern options in terms of dietary supplements or additives. Dairy products would follow a similar pattern, as traditional hard cheesemaking (think of Parmigiano) involved only rennet and salt when other more specific processes resulting other "families" of cheese were not involved (think of partly moldy cheeses like Roquefort or Gorgonzola).

In sum, we might speculate that food in the Middle Ages might have been something similar to what "bio" foods and commodities are defined as today.