by Jason Crawford · March 29, 2020 · 2 min read
In a previous post I wrote about the early stages of agriculture. These stages are defined by a succession of solutions to the fertility problem: every harvest takes fertility out of the soil; without active management, fields lose their productivity over time.
The early stages were all about crop rotation. First, fields would rotate between crops and fallow. Animals were grazed in pasture in the summer, and in winter, fed on hay harvested from the meadow. Later, crops and pasture themselves were rotated. Historian Norman Gras, whose book A History of Agriculture in Europe and America I’m reading now, identifies two further stages: “scientific rotation” and “specialized intensive”.
The term “scientific rotation” seems to me a misnomer; it’s not clear how it depends on science, especially since Gras says that versions of it arose in places including ancient China and medieval Lombardy. Perhaps it could be called “optimized rotation” or “advanced rotation”. In any case, Gras identifies a number of advanced rotation techniques, including:
Planting crops and plowing them under, instead of simply leaving a field fallow. Clover, for example, can be planted and then plowed under instead of harvested, before planting wheat in the following season. The clover decomposes under the soil and provides nutrients for the wheat.
Choosing the rotation to foil weeds and parasites. For instance, wheat, barley and rye can all suffer from “rust”, a fungal disease, and the fungus can stay in the soil after the grain is harvested. It helps to fight the fungus if the wheat is followed by a different plant not susceptible to rust. There is some similar way in which weeds are defeated by rotation; I’m not totally clear on it, but it has to do with the lifecycle of the weed and which crops it matches with, or doesn’t.
Choosing a variety of crops with different root lengths, to use moisture and nutrients at all levels of the soil.
Choosing a portfolio of crops with different growing seasons, to even out labor requirements during the year.
For livestock, switching from grazing on pasture to fodder in the barn. Pasturing is inefficient: the animals don’t eat all the grass in the field, they trample some of it, they leave their droppings in the grass. More efficient is to treat animals like humans: grow their food in the field, harvest it, and feed it to them directly. This also allows you to plan and optimize their diet. Further, manure can be collected directly and used as fertilizer where needed.
In English agricultural history, a well-known “scientific” rotation was the “Norfolk rotation”: clover, wheat, turnips, and barley (in that order). Again, the clover was plowed under for the wheat. The turnips were fodder for livestock.
Gras is less clear on what “specialized intensive” means, although one key sentence reads: “By watering, fertilizing, and heating the ground, by soil pulverization, seed selection, treating seed chemically or bacteriologically, transplanting, protection by glass, and intertillage, enormous crops can be attained.”
Owing to techniques including the above, agricultural productivity grew so fast in Britain from the mid-1600s to mid-1800s that the period is known as the British Agricultural Revolution. Gras is sketchy on details, but a few key ones include:
Natural fertilizers, including imported guano (which you may recall from the story of synthetic fertilizer)
The seed drill, a machine for seeding that placed seeds carefully at regular intervals, in contrast to the primitive method of scattering them by hand
Other machinery for harvesting, including the reaper and the threshing machine
I’m going to have to do more research into the above topics.
(As a reminder, I’m experimenting with a style in which I write shorter and less polished posts more frequently while I’m in the middle of researching a topic. If you don’t have time for these posts, feel free to skim or skip them; at the end of this process I’ll write a more authoritative longform summary of the topic.)
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