I’ve started dabbling in the marshy shallows around the deep pool of my ignorance of the modern history of agriculture, and one thing has become even more obvious.
Mixed farming — mixed species of crop as well as mixed kingdoms of plants and animals — was without a doubt the sine qua non of both phases of the long, slow increases in English farm productivity from about 1500 to 1850 and beyond. 1
I get all this from two fascinating and eminently readable papers by Robert C. Allen. The first 2 uses detailed estimates of nitrogen flows to build a dynamic model that simulates the amount of nitrogen available to plants under various types of management. The second 3 examines a variety of estimates of changes in overall agricultural productivity in England to ask whether there was indeed a revolution, and if so, when did it take place. The result is a much more nuanced picture of how agriculture changed, at least for me.
It starts after the Black Death, when a lack of labour shifted land from arable to pasture and increased the number of animals. “More animals meant more manure, and more manure meant higher grain yields”. Alternatively (or additionally) there’s so called up-and-down or convertible husbandry, in which land alternates between arable and pasture with a fairly long timescale, often measured in decades. Although animals are grazing and dunging on the pasture this is not quite the same as the manure hypothesis, because it is natural deposition and fixation of nitrogen from the air rather than cycling through the animals that increases the amount of nitrogen in pasture soils. Animals, again. And a final factor is the increasing use of legumes, with peas and beans replacing barley and oats as the spring crop, and then the use of clovers and their gradual codification in the famous Norfolk rotation of turnips, barley, clover and wheat. The crucial insight here is not merely that the clover fixed nitrogen, but that it and the turnips supported livestock, whose manure added more nitrogen to the soil stock.
“The barley and wheat produced beer and bread for the people, while the turnips and clover fed sheep and cattle”.
There’s lots more of great interest in the two papers I cited, but for me there are three very clear take-home messages. First, considerable increases in yield took place long before it became possible to add energy-intensive nitrogen directly to the soil, indeed, long before anyone knew anything about the importance of nitrogen as a limiting plant nutrient. Secondly, this depended absolutely on farms and fields using different crops, and livestock played a central role. Finally, it took a long time for yields to rise, but having risen they stayed high.
Any messages in there for current agriculture, do you suppose?
