Liming is the application of to the soil of calcium carbonate, typically in the form of ground limestone. Chalk, marl, shells and hydrated lime are other forms of calcium carbonate used in this application process. Lime neutralizes soil acidity, improves soil texture and increases activity by soil microorganisms. It helps to ensure nitrogen availability for plants and increases available phosphorus. It cannot be added endlessly though, because it will eventually turn your soil alkaline, add too much phosphorus and allow for plants to drain soil’s nitrogen and other nutrients.
Medieval and pre-medieval authors discuss liming using chalk, marl, and ground limestone. Many of the easiest ways to get calcium carbonate are from chalk and marl first, and limestone second, as limestone has to be ground. In this blog I mention marl – because although I have a separate blog on marling, marling is process (which may or may not actually involve marl), and marl is a type of soil.
Varro, in de Re Rustica discusses the use of lime early on: “where they fertilized the land with a white chalk which they dug; where they had no salt, either mineral or marine, but instead of it used salty coals obtained by burning certain kinds of wood. ”
Almost a century later, Pliny the Elder discusses marl more comprehensively – outlining three types, colors and two qualities that different types of marl have. He explained dry marl is best for wet soils, the fat marl for droughty ones, and normal soil can benefit from either grey or chalky lime. He also recommends it is combined with animal waste for improved effectiveness.
The Geoponika suggests using chalk to protect harvested grain from ants, a technique Jan Zadoks thinks might work in Crop Protection in Medieval Agriculture. Chalk and marl were both used in the Muslim world as fertilizer.
During the medieval period, marling was done extensively. Old Norman leases often included rules regarding chalk applications, and 1225 came with a law allowing Englishmen to hold marl pits on their own land. An English record, dating from 1498-1506 at the very end of the medieval period, shows just how effective it was found to be – Humphrey Newton marled his fields for 10 weeks, distributing at least 12 tons of marl on one set of fields alone – which resulted in a “two-fold increase of barley” and increased rents from marled fields as well.
Proper ground limestone liming was a fairly well known practice, as documented by Christopher Dyer, (Medieval Farming and Technology: Conclusion, 1997) and Harriett Bradley (The Enclosures in England an Economic Reconstruction, 1918), and was used regularly.