Source: Soil Science Society of America
Ireland wasn’t always dependent on potatoes, but in the decades leading up to the famine, more farmers started growing potatoes. As a crop, potatoes are inexpensive and high-yielding. As a food, they are packed with calories and nutrients. The Irish potato famine occurred in the mid-1800s, the result of the fungal disease late blight. Let’s look at the scientific factors that contributed to the spread of the disease, and how such a tragedy can be prevented in the future.
Ireland in the mid-1800s was very much an agricultural nation. Its approximately 8 million people were among the poorest people in the Western world. Since their introduction in the 1600s, potatoes had thrived in the cool, moist soils of Ireland. Potatoes were meant to supplement a well-rounded diet of other crops, dairy and meat products.
However, due to historical and economic factors, farmers began to rely completely on the potato for their existence. An acre could yield up to 12 tons of potatoes annually. Although a working farmer could eat up to 14 pounds of potatoes per day, one acre of potatoes was enough to feed a family of six for a year. Potatoes are rich in protein, carbohydrates, minerals and vitamins. This meant an Irish farm family could stay healthy on a diet of potatoes alone. By 1845, massive amounts of potatoes were grown in Ireland, with little attempt made to plant any other crops. Even more unfortunately, farmers were growing a potato monoculture in their fields, meaning that they were growing only one variety of the crop.
The potato famine began in September 1845 as leaves on potato plants suddenly turned black and curled. Late blight spread like lightning. A single infected potato plant could infect thousands more in just a few days. Potatoes dug out of the ground at first looked edible, but shriveled and rotted within days. The results were devastating, as starving tenant families nationwide were evicted from their lands. By 1851, an estimated 1.5 million Irish people had died from the effects of the famine, with the highest death rates among children under five years of age and the elderly.
Scientists have since attributed the potato blight to a strain of the fungus Phytophthora infestans, which infects the plant through its leaves. It leaves behind shriveled, inedible tubers. It took until 2013 to correctly identify the P. infestans strain as HERB-1. Improvements in crop breeding since the 1850s have yielded resistant potato varieties, stopping the deadly infection in its tracks. Scientists believe the HERB-1 strain is now extinct.
Just like meningitis can travel quickly through college dorms, HERB-1 spread quickly over the Irish potato fields. With each plant being the same, there were no breaks to stop HERB-1 from infecting neighboring plants. In addition, with all fields planted with the same crop, Irish farmers were dependent on the income—and sustenance—of their only crop. When the crop failed, the farmers failed.
Fungus in soil is not unusual. In fact, bacteria, fungi and other microbes commonly live in healthy soil. When there is a variety of plant life growing in the soil, there is usually a natural balance in this microbial community. However, a continuous planting of the same crop—in this case, Irish Lumper potatoes—can cause an imbalance in the soil microbial community. With little diversity of soil microbes, there was little resistance to fight the disease. You might be familiar with this in humans, where some doctors recommend we take probiotics to maintain balance in our gut microbes. To learn more about soil microbes, read this blog, and view this video.
Why did growers move to using only one crop—the monoculture system? In theory, cultivating a small number of crops over large areas improves efficiency. Farmers need only buy one type of seed and store one type of crop. Crop management might all be the same. With more efficient farms came increased profitability to a business that involves countless hours of difficult, physical labor.
While it increased efficiency and helped farmers become profitable, monoculture systems have huge drawbacks, as evidenced by the Irish Potato Famine. Large, homogeneous crops enable bacteria, viruses, fungi and insects to specialize on one specific host. This kills the entire crop and increases the chance that these microbes could mutate into an even more harmful variety.
In the 150 years since the Irish Potato Famine, hunger has continued to wreak havoc in the world. An estimated 200 million children under five years of age suffer from chronic malnutrition. Ten million people are reported to die each year from hunger-related causes. Science has brought genetic improvements and agronomic advances worldwide, but hunger and famine are still here. Those people living in hunger-prone areas of Africa and Asia still live under the specter of crop failure. Threats arise from multiple causes, including climate change and poor seed stock, but are exacerbated by monoculture.
There is no straightforward solution on how to reap the economic benefits of monoculture while eliminating its negative impacts. However, farmers worldwide are increasingly moving to the practice of crop rotation. Farmers plant one crop in an area one year, then switch to another the following growing season. This helps reduce possible infestations with crop diseases. It can help soil quality. Crop rotation makes things more complicated for the farmer who has so far relied on monocultures, but successful, sustainable, productive crop rotation practices already exist around the world.
Another farming technique that can help plants fight disease is called intercropping. In this type of system, a second crop is added in between rows of another crop. There are multiple benefits to intercropping, but one of them is that the crops tend to act as barriers for the spread of disease, working like a Band-Aid might halt the spread infection on your skin.
Long-term practice of monoculture, specifically with the Lumper potato, made the plants in Irish fields more susceptible to disease. When the HERB-1 fungus arrived on Irish soil, conditions were ripe for the fungus to thrive at the expense of farmers and their families. Armed with this knowledge, researchers and farmers alike are improving and adopting practices like crop rotation, intercropping and increased crop diversity. This argues for diversity in the world’s crops to reduce hunger and starvation, even if this entails lower yields.