From EROI to EROLI: energy return on Land investment ? 2/2

In the agricultural project that I described in my previous contribution [1], which was initially about the EROI, the energy return on energy investment, I subsequently calculated the effects back to land’input’. But then the thought soon arised: would is also be possible to develop a LROLI, a Land return on Land investment’? Say the ratio between land use for the input of the cultivation (energy labor, raw material expressed in land, cq space time), compared to the yield of 1 ha of land? This is speculative, and open to discussion, but still an attempt to give an impetus for this.

Take for example 1 hectare that is sown manually, from the yield of the year before. And suppose someone spends 1 month doing that, hoeing, sowing, etc. And then another 1 month of harvesting. Then the input is two months of labor energy, or the equivalent of food energy for that, which in turn represents an amount of land (yield). In this project, 0.0175 GJ/worked hour was used, i.e. for 2 months of work, adding up to 5.6 GJ . In case of the potato example from the project, the local output is 148GJ/ha of food energy. So, converted, 0.037 ha input is needed ( for the food energy) , and the net output in land is then 0.963, being the land return on Land input, the LROLI.

By the way, here is calculated with the output of 1 hectare of high energy intensive agriculture, and not as a yield of only hand labor. That should be less. At least, that’s what I assumed. However, I read on websites of various hobby growers that they get 4 kg potatoes per m2. That would also add up to 40 tons per hectare. In other words, the same yield would be achievable with both high-intensity farming as well as with manual labor.

So on the one hand, the difference is the labor time: it is low in the case of high-intensity agriculture (see figures report) , because of the use of machines and fertilizers etcs, which replaced labor. But on the other hand the difference is outsourced in footprint, to production of all those machines and fertilizers, pesticides and more, leading to a much larger land use, leaving little net result.

So it is much more effective to use more labor. But where does one get the labor? That seems to be an optimization problem. If we return to agriculture using labor, a lot of other labor will be superfluous, such as production of tractors, other machines and growing materials. That will not be enough, but is a start. Smits calculated that about 50,000 extra people would be needed in labor if Dutch agriculture were to work effectively. [2] These people would not be able to work elsewhere, such as in “export”, which is intended to support the growth of GNP. But the imports will also be a lot lower, for agriculture itself, but also for the then smaller production space for other things because of labor shifts. GNP will be lower, but so will the environmental burden; we will then be within the natural potential of the system, and avoid plundering resources elsewhere and depleting the soil.

An additional problem is of course that these people must be willing to work in agriculture. That seems to contradict the migration to cities for the sake of it, but well, that’s another tack.

For calculating labor energy, Smits’ conversion factor has been used, assuming a family to be fed and total number of hours to be fed. Calculated 1:1 in terms of labor, less land is needed to produce less energy. This needs to be calculated again.

If we apply the principle from the original figures of the report from part 1, of high intensive cultivation, with almost 7 ha input for 1 ha (comparable) output, then the potato hectare would have an LROLI of 1/7= 0.14. [3]

What does that mean? That in fact only a net 0.14 ha is effectively used. Or, if you consider it globally, we may have a high output per hectare, but effectively only have 1/7 of the number of hectares available. The rest goes into secondary conversions and intermediate products*. So while a hobby farmer can get close to the same output, but instead with an LROLI of 0.96 , compared to the 0.14.

The comparison between the vegetable garden hectare and High-Technology hectare works well, because both assumed to have the same output. On closer inspection, however, the methodology unfortunately does not generally hold true, with such a LROLI. It is not just the hectare of input versus the 1 hectare of output, the output itself in food energy can be quite different, and then the comparison is not entirely valid: if you spend half a hectare extra on required input, and the output is twice as large, then the yield over the 1.5 hectare has still increased per hectare, which is not visible in the comparison. So the LROLI is not going to work, at least I haven’t found a way to keep the comparison pure.


But what could work is a combination of EROI and LROLI: the EROLI: The Energy Return on Land investment: and since land is the great divider, between the earth system and the solar energy input, that does work: how much land is needed for how much output. And then the figures from the first part of this study, where I already converted to direct and indirect land, are useful: then the output of the high-tech variant is 148 GJ minus the energy input, 33.6, is 114.4 GJ. Distributed over 6.5 ha of direct and indirect land, the EROLI is then 22.7 . So in fact only 22.7 GJ of food energy per hectare becomes available, 7 times less than what agriculture keeps on predicting. And then the world food supply can no longer be taken for granted!

The vegetable garden of the above would then result in a harvest of 148 GJ on 1 hectare plus investment of 0.037 ha, gives an EROLI of 142.7 . That is more like it. (For potatoes, that is.)

In an earlier phase of the ‘Enriching Agriculture’ project I calculated that for a food-forest the output could be at least 89 GJ/ha, and then only counted with the trees harvest, especially trees with walnuts and apples. [4] The contribution of the lower layers not yet included. The labor input for this would be 2/7 person-years ( limited maintenance and harvesting) . Again, using Smits’ conversion factor, this comes down to 8 GJ input per year of input**. This puts the EROI at about 11. In land: 0.09 ha is needed for input, so the EROLI is 81 , compared to 22 for current agriculture! Les then the vegetable garden option, but firstly this is without the lower layers output ( berries etc) and providing other services, like biodiversity, green cover, and possibly part of biobased materials.

Incidentally, these are the kinds of calculations that were in fact normative before the industrial revolution: an ox could also be used for ploughing, but that again took up food-land. In the literature examples can be found of cities getting into trouble because the required food supplies were no longer sufficient, partly due to the food demand for oxen, because of the use of oxen for ploughing but also the transport by oxen to ever more distant fields, the whole process had its limits. Ultimately its all about a food-land-time problem. (Read for example the very interesting book “In the servitude of power”, which discusses this in detail.[5])

This EROLI calculation seems an interesting approach, not in the least because we are going to depend mostly on solar energy, directly or indirectly ( wind, hydro) , and thus it could be that optimizing to land is an effective method. To calculate , balanced across various climates and various food and plant species, the potential yield of land, say determining the planetary limit of potential, in an understandable unit.

But as I said, this is a first attempt to give hands and feet to a train of thought, so I’m curious to hear others’ viewpoints on this.



* Of course, at present it is not land that is directly occupied, but primarily fossil fuels, which of course once had land use as a basis for their formation from biomass. So we are relying on historical geological land occupation, with however the negative side effects of that such as climate change.

** In the original article about the food forest, the calculation was not based on Smits’ conversion factor, but purely on the work energy of 2 months of work by 1 person (instead of a family), being 1 GJ/year, and then the EROI comes out at 89!) [4], and the EROLI at 88.


[1] part 1:

[2] report eroi potato growing:

[3] De duurzaamheid van de Nederlandse landbouw : 1950 – 2015 – 2040, Meino Smit, 2018 WUR, isbn 9789463432894; 9463432892 ,

[4] EROI food systems and food-forest:

[5] In the servitude of power, energy and civilization through the ages, Debeir, Deleage, Hemery. 1991, Isbn 0862329434

Author: ronald rovers