EROI and land use of potato crop – a pilot 1/2

In a recent project , ‘Verrijkende Landbouw’ ( Enriching Agriculture) [1], I was able to refine the theory and methodology of MAXergy, using Embodied Land as an indicator [2], thanks to a practical pilot. As follows.

Agriculture needs to change. That should be obvious by now. And not only regarding ‘livestock’ but also the ordinary agriculture, highly mechanised crop growing.And this is not about ‘farmers’, but about how and what to farm. Which currently is not done in a sustainable way, but by a profit-maximizing system driven agriculture, completely disconnected from physical or ecological optimizations. Mainly relying on imports and exports of raw materials and energy*. Anyway, it is clear that this has to change. But how. The Enriching Agriculture project examined that: how to get from plan A , the current agriculture, to plan B, the future model. A study on Value, Land and Human, and the final report has now been published. [3]

It will not surprise you that in that project I mainly looked at the energy component (in conjunction with materials) : Energy output versus energy input, EROI, or EROEI (energy return on energy investment), and from there to land use: Embodied Land, directly and indirectly. And within this project there was the opportunity to carry out a pilot: can we map that for a particular crop, per hectare, per farm or region. Previous studies have been averages for the whole sector, or at least by sub-sector. For example, Smit’s study showed that for the sector as a whole, 6 times more energy went in than came out in food energy[4]. Now the idea was to start from the bottom up, per hectare and per crop, in order to investigate plan B for a hectare.

Of course, this starts with the simple data. After a preliminary study, it turned out to be useful, for example, not to rank things by farm, but purely by hectare, in order to build the method from there. That first pilot is now finished, and was mainly concerned with developing the methodology and a first indication of the impacts at per input category, so that we can make recommendations based on that. And that first mapped hectare as a pilot concerned potato cultivation. Not entirely surprising, in a country of potato eaters, is it? And it is not surprising that it is the crop with about the highest yield per hectare. The simplest question is of course: “What is the yield? That varies a bit according to variety and soil, but in this study, 40 tons of potatoes were taken, and at 3.7 GJ/ton, that yields 148 GJ/ha per year in food energy.

But what has been put in, to get that done? A lot of work of course, especially mechanical. In addition to raw materials, animal manure, fertilizers, pesticides (also called ‘plant protection products’) and other substances to keep the soil free and workable. All that work and those substances again cost energy and raw materials. So this has been mapped out as much as possible (although not all figures were available, but the main ones were sufficient for this pilot). Incidentally, it was not just about 1st order effects but also as many 2nd order effects as possible, such as in addition to the impact of the fertilizer itself also the impact of labor in the fertilizer plant, the plant itself, etc.

And here and there I was quite surprised: Do you know how long it takes to harvest 1 hectare of potatoes? Half an hour! Two soccer fields : lightning fast, thanks to enormous mechanical violence input.

It turns out that at least 33.6 GJ/ha of energy is used. Minimal, because some figures are missing, but that leads to an EROEI of about 4.4: a factor of 4.4 more comes out than goes in, in energy that is. Which is only just on the positive side. Studies show that an energy system should actually have an EROI of 10, to be able to cover the losses of the system that still occur after harvest, and to actually have a profit left over, with not too many resources used. An EROI of 3 is considered the absolute minimum. After harvesting, consider storage, transport, cooling, supermarkets and cooking, as moments where energy losses occur.

In the case of potatoes, irrigation, animal manure and the spraying of phytoftera proved to be major contributors to the input.

This does not look promising for many other crops, with lower yields.

Land use was also considered: The land use of the cultivation of 1 hectare of potatoes is 1 hectare for the cultivation itself, and 0.5 hectare for the direct additional input of raw materials and fuels. The yield of 1 hectare is therefore in fact the yield of 1.5 hectares. The largest contributions come from various treatments and irrigation (such as the surface needed for the rainwater cycle, or energy generation with rapeseed oil, for example, see below).

There is also indirect land use: mainly due to the depletion of raw material stocks, and the (biomass) energy needed to restore these stocks. And in the case of metals this rises sharply: for machinery in particular it is an extra of almost 5 hectares in the case of potato cultivation. (See background in pilot report EROI [5])

potato cultivation overall:

If we include the direct land use in the calculation (that 1.5 ha), then the yield per hectare drops from 148 to 99 GJ/ha and the EROI drops to 2.9 , thus coming under 3.

If we also include indirect land use, then the EROI drops to 0.68. In other words, more energy goes in than comes out. After all, land is lost energy. So even the cultivation of potatoes is not effective in its current form, if we include everything,

Diesel Land

Interesting to note is that land use includes a tractor’s diesel, but calculated as if it were already supplied from a renewable source, say as bioenergy, from rapeseed land. As follows:

In terms of energy, a tractor uses an average of 20 liters of diesel per hour, or 0.72 GJ/hour. We can convert fossil oil to land use, but here we have chosen to start from the inevitable future, that energy should come from renewable sources, exit fossil, and thus biodiesel for example. That can be obtained from rapeseed, and at 4 tons per hectare yields ~1400 ltr of diesel per year per hectare. Of that, an estimated 50% is taken as net efficiency ( of course, rapeseed production has also had energy inputs, as well as losses during diesel production)

In short 1 ltr of bio-diesel has a land use of 0,00142 ha . Or as in the calculation where the tractor hours are taken into account: 1 hour of tractor work results in a land use of 0.0285, or 285 m2/hour of tractor work. (That does not include the energy/land use of a driver hour).

Which is what triggered me to use the MAXergy methodology to do more land calculations: until now I had mostly used solar panels as a reference to convert energy flows to land use. Which of course complicates matters, because those panels themselves also have an impact that needs to be taken into account, up to and including the land impact of extracting raw materials. And since I came to the conclusion earlier that biomass growth is the reference of sustainable growth here on earth, that is very cumbersome and it is therefore much smarter and logical to convert directly to biomass growth, as for diesel but also to use that route instead of the solar panel route with respect to other energy use. (This has been further elaborated for other feedstocks, as I described earlier, see [2])

More on landuse in part 2 to come. The partial report of the pilot can be downloaded here [5], and report of the larger project here [3].


* strange thing actually: we get from whole world food here, and then export for a large part result. What’s left is some money. Might as well have done it locally elsewhere, and only send the money to NL. It would have saved a lot of energy and transport costs. Moreover, the employment is nonsense, we are short of people in basic facilities, so to use them for import and export…


[1] Enriching Agriculture web: (Dutch)

[2] Maxergy 3.0

[3] VL report:

[4] The sustainability of Dutch agriculture : 1950 – 2015 – 2040, Meino Smit, 2018 WUR, isbn 9789463432894; 9463432892 ,

[5] part report eroi potato crop: (Dutch)

Author: ronald rovers