Potato Math

Quote of the Day

Being president is like running a cemetery -- you've got a lot of people under you and nobody's listening.

— Bill Clinton


I have taken a break from blogging to do some traveling. The highlight of my travels has been a bus trip around Ireland. It was great! We spent 8 days on a bus driving all over Ireland (see Figure 1). We also spent 4 days on driving around Ireland on our own. I must admit that driving on the left-hand side initially worried me, but after a day of careful, thoughtful driving it started to feel normal.

Figure 1: Our Bus Ride Around Ireland.

Figure 1: Our Bus Ride Around Ireland.

The Irish could not have been nicer, but things are not easy over there. Their economy is in a shambles and the cost of living there is high -- I read a news article that stated that Ireland has the fifth highest cost of living in the EU. They have many of the same economic complaints as the folks in the US:

  • clueless politicians
  • corrupt bankers
  • no one to hold accountable

In the case of the Irish, their sadness is particularly profound because many feel that their chief export today is their young people – just as during the Irish Famine. Thank goodness that Australia has work for some of them. However, losing your young people because of economic conditions is a terrible thing to say about an economy.

During our trip, the impact of the potato on Irish history could not be ignored. While I have no Irish ancestry (my wife has all the Irish blood), I do feel a kinship with the Irish in regards to the potato. I was raised in a small town that was surrounded by potato fields, my brother was a potato farmer, and I worked on a potato farm to earn money for college. When I was a boy, the potato farmers would proudly boast that no crop produced calories per acre like the potato. While apple growers may take exception, the potato does beat the grain crops handily. Consider the data in Table 1 for irrigated crops today. Yields at the time of the Irish Famine were substantially less.

Millions of Kilocalories Per Acre By Crop
Crop Millions of Kilocalories Per Acre
Soybeans 2.1
Wheat 6.4
Corn 12.3
Potatoes 17.8

Potatoes were the calorie per acre leader back in 1846 as well.

Our bus stopped by the Irish National Famine Museum. It was very impressive place that provided us some insight to the living conditions at that time. During our tour, our guide discussed a number of Irish Famine facts:

  • The landlords made their money by exporting all the corn, wheat, barley, and oats the Irish farmers grew. The Irish grew potatoes to feed themselves.
    This meant that the Irish subsisted on the potatoes and dairy products that they could grow on their land. Remarkably, potatoes and a bit of dairy will provide a nutritious diet (Reference)
  • At the time of the Famine, an average Irish farmer consumed ~14 pounds of potatoes a day (Reference).
    While this seems like a lot of potatoes, the calories work out about right for a person doing hard manual labor.
  • During the depths of the Famine, potato yields dropped to 1/7th of their pre-Famine levels (Reference).
  • The Famine Museum is on an old farm site at which there were 5000 tenant farmers on 30,000 acres, with an average of 6 acres for each farmer.
    This is a very small amount of land on which to support a family. I failed to find a good reference for the average family size prior to the Famine. I found one economic reference that used an average family size of five (Reference), but that was lower than some reports. For example, I have seen forum discussions that estimated average family at eight or more (Reference).
  • When the potato blight hit, the landlord ordered his tenant farmer to switch from growing potatoes to oats.
    Oats turned out to be completely inadequate as a food source and starvation set in. The landlord began to fear for his life as the starving masses began to rise up. It turned out he did have something to fear as one of his tenants eventually did kill him.

Let's examine that calories per acre question a bit closer. How big an impact did the switch from potatoes to oats have on calorie production?.


Our Famine Museum tour guide mentioned that potatoes produce 2.5 times more calories per acre than oats. Let's try to understand where this number comes from because it is critical to understanding the Famine.

  • I will assume an average of 9 tons of potatoes per acre.
    Prior to the start of the Irish Famine, Irish potato yields varied from 6 to 12 tons per acre (6 ton Reference, 12 ton Reference).Agricultural yields are highly variable because of soil conditions, weather, crop enemies (insects, rodents, fungi, etc), and agricultural practices (e.g. availability of manure for fertilizer and water for irrigation).
  • Potatos provide 77 kilocalories per 100 grams (Reference).
    Potatoes are between 75% and 80% water, which makes their calories density appear to be low. However, potatoes still produce the greatest number of calories per acre for a standard field crops (apple growers like to claim the title of most calories per acre for any crop)
  • I will assume an average of 39 imperial bushels of oats per acre (Reference) and 40 pounds of oats per imperial bushel (Reference).
  • Oats provide 389 kilocalories per 100 grams (Reference)

Given this information, the calorie comparison between potatoes and oats can be performed as shown in Figure 2.

Figure 2: Comparison of the Calories Per Acre Between Potatoes and Oats.

Figure 2: Comparison of the Calories Per Acre Between Potatoes and Oats.

So I now understand the calorie difference between potatoes and oats. If we assume that the Irish tenant farmers were growing their personal food on the same acreage as before, the switch from potatoes to oats meant that the land could now only support 40% of the existing population. One solution to the problem would have been to stop exporting crops and use those crops to feed the Irish. The landlords did not do this. They simply chose to let the Irish starve.


Sadly, the Irish Famine was completely unnecessary. It turns out that there was plenty of food in Ireland to feed the people, but the landlords needed to export the food in order to keep their incomes up. The attitude of the government is summed up by the following quote (Reference).

The economists then concluded that since all the demand side measures had failed, nothing could be done. The only way to prevent future famines was to reduce demand, by “letting nature take its course”. “‘I have always felt a certain horror of political economists,’ said Benjamin Jowett, the celebrated Master of Balliol, ‘since I heard one of them say that he feared the famine of 1848 in Ireland would not kill more than a million people, and that would scarcely be enough to do much good.’ The political economist in question was Nassau Senior, one of the Government’s advisers on economic affairs.” (Woodham-Smith 1991 pp 375-6). He need not have worried: 2.5 million people died out of a population of 8 million.

You might wonder how the British were able to export food with starving people all around. Here is another quote that describes that situation (Reference).

Ireland starved because its food, from 40 to 70 shiploads per day, was removed at gunpoint by 12,000 British constables reinforced by the British militia, battleships, excise vessels, Coast Guard and by 200,000 British soldiers (100,000 at any given moment)

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2 Responses to Potato Math

  1. robjford says:

    Problem was that the subsistence farmers had no money left to pay for the huge increase in food costs nor to pay their rent. No rent paid and they were turned off their smallholdings. No home, no money and no food source. They also had no money to buy oat seed nor time to wait and starve through a year until the oat crops might arrive.

    A more balanced history of the famine is given in link:

    If you take time to consider the attitudes of the British Government of the day you hear the same heartless thoughts being expressed by modern day conservatives in USA.


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