What really drew me in when I first started reading Maoyuu was its broad look at the physical and social sciences. It looks into politics, agriculture, economics. There is a real intent in the series to teach fundamentals, and the engineer in me loves it. So with this episode, a single minute is devoted to a very important concept in agriculture: Crop Rotation. With this concept, The Demon King will set in motion her plan to change the human world. But why is crop rotation so important? Let me explain.
A critical element to plant growth in earth’s biosphere is nitrogen. The Nitrogen Cycle is “the process by which nitrogen is converted between its various chemical forms”. Nitrogen transformation can be carried out through both biological and physical processes. The majority of Earth’s atmosphere is nitrogen, however, atmospheric nitrogen cannot easily be converted for use by plants. nitrogen (and it’s derivatives that we’ll talk about later) can be depleted from the soil quickly if certain biological process do not take place. Farming techniques developed by humans can also deplete the soil of the necessary chemicals for proper plant growth. A diagram of the Nitrogen Cycle is shown below.
As noted in the diagram, many factor influence the migration and transformation of nitrogen in the soil. Most plants draw nitrogen derivatives from the soil, like Ammonia and Nitrates. Bacteria and fungi provide an essential role of producing these derivatives as a part of their biological process or decomposition. Some plants are nitrogen fixing; they store nitrogen in their root system returning some of the atmospheric nitrogen to the soil. Animal manure is also a great source for material that fungi and bacteria can feed off, returning necessary chemicals back to the soil.
If you’ve ever owned a house, you done a little nitrogen improvement for your yard from time to time. If you’ve ever put fertilizer in your yard, you’ve done something to contribute to the Nitrogen Cycle. There are three (3) values listed on the common bag of fertilizer. The values represent the percentage the product contains by volume of nitrogen (chemical symbol N), Phosphorus (P), and Potassium (K). By selecting the right percentage, you can restore lost elements necessary to maintaining the Nitrogen Cycle and keeping your lawn green. A common fertilizer, commonly call “Triple 16”, contains an even 16% by volume of each of these elements.
If you’ve ever wondered why your dog leaves spots in your yard, here’s why: urine, when produced as a waste product in animals, contains a high level of nitrogen. You’ll have a dead spot (extreme nitrogen in the grass killing it) surrounded by a ring of green grass (above normal nitrogen, leading to rapid growth).
So what does this have to do with crop rotation? Different plants can play different roles within the Nitrogen Cycle. By playing into the different strengths of plants, you can improve their chances for growth. Crop Rotation is “the practice of growing a series of dissimilar/different types of crops in the same area in sequential seasons.” Rotating crops can replenish nitrogen in the soil, and help prevents the build-up of pathogens and pests that often occur when one plant or crop is continuously planted.
Crop Rotation has been used in farming almost since farming first started. Ancient farmers found growing the same crops in the same position caused a buildup of pests and a reduction in fertility. So the solution was to grow a winter crop, and then summer crop, and finally leave the ground for one growing season to recover. This three-year system was commonly used in Europe until the 16th Century. And this is the system we find present in Maoyuu. Her solution is to change this to a four (4) crop rotation, which will fundamentally change what this tiny region can produce. The system she proposes was made popular by the British agriculturist Charles Townshend in the 18th century. The system (wheat, turnips, barley and clover), creates staples necessary for livestock to be bred year-round. The four-field crop rotation was a key development in the British Agricultural Revolution.
Each crop not only provides food for a consumer (livestock or human), but also plays a role in the crop rotation and Nitrogen Cycle:
- Wheat is a basic ingredient in any bread product. It makes for an easy consumable for human consumption. Wheat is a good winter leacher of nitrogen, which is slowly released once the tops are cut off during harvest, allowing for a follow on crop.
- Turnips are a root crop, and deplete very little nitrogen from the soil. Turnips can be easily stored in the winter months.
- Barely is a cool-weather cereal grain. It functions well as a winter crop alternative to wheat. Barely is primarily used a livestock feed.
- Clover is a nitrogen fixer, as it pulls nitrogen from the air and store it in the roots. This is done with nodules on the roots that contain nitrogen fixing bacteria. This insures there will be lots of nitrogen available for the next plant in the rotation.
As one last improvement to the crop-cycle, she has pigs grazing in the clover fields. The manure left by pigs provides a big boost in nitrogen and other chemicals to the soil. It also improves water retention when tilled in. And as the Demon King mentions, it provides ample feed, improving the size of the pig the butcher-able meat.
Failure to Rotate?
But what happens when a proper crop rotation is not maintained? In the 1930’s in North America, an event now known as the Dust Bowl occurred. The Dust Bowl “was a period of severe dust storms causing major ecological and agricultural damage to American and Canadian prairie lands in the 1930s, particularly in 1934 and 1936. The phenomenon was caused by severe drought combined with farming methods that did not include crop rotation, fallow fields, cover crops, soil terracing and wind-breaking trees to prevent wind erosion”. During an already tumultuous economic time, this devastated the agriculture community, making the Great Depression all that much worse.
Back to the anime. In the cold weather climate that the Demon King has chosen to set up her agricultural revolution, this rotation is nearly perfect. It provides a food source for livestock and farmer, and can be easily accomplished in the available land and climate. An improvement in pest and weed control could be used, but for the technology of the era, this might be beyond the scope. As we’ll soon see, these changes, along with next week’s hinted surprise, will lead to widespread changes. But I won’t spoil the surprise for the rest of you.