‘Restoration Agriculture’ Part II: annual monocultures out-calorie perennial polycultures!

In this post, I’m going to complete my look at Mark Shepard’s book Restoration Agriculture: Real World Permaculture for Farmers, which I began in my previous post. My focus here is on Shepard’s analysis of the productivity of perennial polycultures – a subject dear to the heart of many a permaculturist.

In the chapter titled ‘Nutrition and Perennial Agriculture’ (pp.167-183), Shepard writes “The nutrition per acre under restoration agriculture outcompetes corn so much that it’s not even funny” (p.167). Let’s consider this in more detail.

Shepard is actually making three different arguments in this short sentence, two of which I find convincing and one of which I don’t. The first is that a mixed ‘restoration agriculture’ holding produces a more nutritionally complete and balanced diet than a corn monoculture. That’s not something I’ll dispute. Perhaps it’s not something anyone would dispute – I doubt even the most dogmatic proponent of agribusiness-as-usual would argue that a pure corn diet is a good idea. I guess a pure chestnut diet wouldn’t be so great either. But I think it’s true that the mainstream farming system is producing too much of a narrow range of crops which are not nutritionally optimal.

The second argument is that mainstream agriculture wastes a lot of its productivity in inefficient uses: primarily livestock fodder and biofuels. The claim that we need conventional arable annual farming in order to ‘feed the world’ indeed rings hollow when we use so much of its product to feed bio-digesters and livestock that service the demands of the wealthy, and Shepard makes that point convincingly. According to his figures, a corn monoculture can produce 13.9 million calories per acre, but the actual human nutrition derived from it (ie. direct plant food plus indirect food from corn-fed livestock) comes in at only 3.06 million calories per acre. That is a shocking discrepancy indeed, but what are its implications for the calorific productivity of an acre of corn? Zilch. Feed it to livestock, feed it to digesters, dump it in the sea, do any damn fool thing you like with it, but the productivity of a field of corn remains 13.9 million calories per acre. Don’t blame corn for what happens to it beyond the farm gate.

That last point is relevant to Shepard’s third argument, which is that an acre of restoration perennial polyculture outyields an acre of corn calorifically. Calories are important in debating different possible agricultural systems because it’s not an easy thing to get enough energy into the bodies of 7 billion humans, and proposals for agricultural systems that are unable to furnish the necessary calories are not an easy sell. So I’m glad that Shepard has bitten the bullet.

The productivity figure he uses for an annual corn monoculture in his comparison with a perennial polyculture is 3.06 million calories per acre (ie. that proportion of the US corn crop currently used directly for human food – see above). But the one he should be using is 13.9 million calories (the full calorific productivity of an acre of corn – incidentally, I’m mostly just using Shepard’s own reported figures here without corroborating them independently). Let’s now look at Shepard’s perennial productivity figures.

It’s worth pointing out that Shepard’s analysis is not based on actual results from a real live polyculture, but on data aggregated from various sources in the research literature. And it’s also worth pointing out that he’s chosen a maximally energy-productive combination of tree crops, including 86 chestnut trees, 208 hazels and 34 apple trees per acre. He claims a per acre productivity of 1000lbs for the chestnuts, which may not be unreasonable, although elsewhere in the book he states “Out of the thousands of Chinese chestnuts that have been planted at New Forest Farm in the past 15 years, only two of them are bearing” (p.81). This, and a few other considerations, provoke the thought that his reported productivity figures may be a touch on the high side, but let’s take him at his word when he says, in addition to the chestnuts, his system will produce about 2,900lbs of apples per acre, 400lbs of hazelnuts, 400 quarts of raspberries, 5,200lbs of redcurrants and 600lbs of grapes. By his calculations, that amounts to about 4.6 million calories per acre of fruit and nut crops.

There are also livestock grazing on perennial pasture alleys between the fruit and nut crops in Shepard’s system – a dairy cow, a beef steer, two pigs, two sheep and ten chickens, which he estimates will produce about 1,100lbs of meat and 2,100 gallons of milk per acre per year, providing another 1.1 million calories per year. Although he makes some good points about the complementarity of the different livestock species and the high returns from high stocking density, I’ve got to say that I find this an unfeasibly high return of meat and milk to expect to produce each year entirely from a 60x60m plot of perennial forage. But let’s go with it anyway – Shepard’s total system then produces by his estimation about 5.7 million calories per acre.

The conclusion I’d draw from this analysis is that if you choose the most calorifically productive perennial polyculture imaginable and then stretch its projected productivity to or beyond the limit of credulity, you can demonstrate that it’ll produce something like 40% the calories of a corresponding acre of annual corn. So the fact is, despite Shepard’s claims, a perennial polyculture under restoration agriculture is less calorifically productive than an annual monoculture of corn by a distance.

Does it matter? Yes and no, in my opinion. No, because of the following (admittedly simplistic) calculation. Taking the FAO figure of about 3.4×109 acres of arable land globally, and assuming the need for a daily calorific intake of 2200 calories for each of the 7 billion people on the planet, that would require a calorific productivity of about 1.7 million calories per acre – comfortably less than Shepard’s 5.7 million figure. Obviously some parts of the world could probably produce a lot more calories per acre of perennial crops than Shepard’s figure, others a lot less. Anyway, I’m reasonably happy to go along with his fundamental conclusion: yes, we can probably feed the world calorifically (and in every other way) with perennial polycultures. Especially if more people spend a bit more of their time working on them.

But the inferior calorific productivity of perennial polycultures does still matter, if only because there are lots of people in the alternative farming movement – including Mark Shepard – who persist in claiming that perennials outperform annuals on this measure when they manifestly do not. Why bring discredit on ourselves by making claims that are patently false when we don’t even need them to be true in order to justify what we’re doing? That matters.

Shepard draws the following conclusions about his proposed restoration agriculture system (p.180):

  1. It produces more than twice the human calories per acre as an acre of corn
  2. It is perennial and never needs to be planted again
  3. It prevents erosion [and] creates soil
  4. [It] can be managed with no fossil fuel inputs

I’m less sanguine. As I’ve just shown, in fact it produces far fewer calories per acre than corn, though not so few as to undermine its plausibility as an alternative to annual agricultures. Some of it will probably need to be planted again, though admittedly much less than an acre of corn. It will certainly do a better job of preventing erosion (though I do worry a bit about those livestock densities). Creating soil? Well, maybe. And yes it can be managed with no fossil fuel inputs, but then so can an acre of corn. Personally I wouldn’t fancy growing an acre of corn without motorised assistance, but nor would I fancy dealing with 1,400lbs of nuts and 8 or 9,000lbs of fruit.

I’m not sure how the human labour involved in the two cases stacks up. Shepard makes some interesting points about the possibilities, as yet unrealised, of mechanical harvesting in a multistorey perennial polyculture. I think he’s right that this may be possible, though I suspect not easy (surely there will be tradeoffs between the degree of polyculture ‘mimicry’ and ease of harvesting) and probably not especially efficient in terms of energy input/output ratios.

People do tend to wax lyrical about the work-free productivity of forest gardens, fruit forests, perennial polycultures or whatever you want to call them. I’m not yet convinced – I’d like to see some good figures. My sense is that there’s a lot of fiddly work involved in maintaining and harvesting these systems, including managing the successional dynamics of complex polycultures, which tends to go unaccounted in the enthusiasm of their proponents. I think our agrarian ancestors figured out correctly that, in most places at least, the best terms of the input/output equation are to be had from growing annual cereals, in the short run at least. Longer term, that approach has stacked up a host of problems for us, and there’s a lot to be said for moving towards perennial polycultures to remedy them. Increasing calorific productivity or saving ourselves work aren’t, however, among them. That’s why I prefaced this topic in my previous post with that neat quote from the Kansan farmer: “Let us not spend Nature’s accumulated fortune in riotous farming”. My contemporary take on that in the light of Shepard’s analysis would be: “Let us not pretend we can protect Nature’s accumulated fortune while continuing to farm riotously”. Or, “there’s no such thing as a free lunch”. If we’re going to embrace a perennial polycultural agriculture – and Shepard provides a lot of good reasons why we should – then we must also embrace working harder for less return.

Indeed, one of the attractive features about perennial polyculture is its affinity with smaller-scale more rural societies and a more peopled agricultural landscape. Bring it on, I say. But maybe grow a bit of squash along the way. Maybe make some weaker claims for the advantages of perennials and the evils of annuals. Mark, I’m with you most of the way, but I just don’t buy the simplicity of your mantra ‘perennials good, annuals bad’.

28 thoughts on “‘Restoration Agriculture’ Part II: annual monocultures out-calorie perennial polycultures!

  1. Such wisdom. Fine tuned too. When is your book coming out?

    Oh, singlehandedly caring for an acre or two of corn without machinery – quite doable. Desirability of such a task given today’s commodity prices… not so much.

    But today’s quibble falls to the following sentence:
    “But I think it’s true that the mainstream farming system is producing too much of a narrow range of crops which are not nutritionally optimal.”

    Desirability aside, a pulse and cereal diet can be nutritionally very satisfying. The amino acid balance in the proteins of the two complement each other. Oils and carbohydrates… fiber, they’re all there. Variety is a great thing (the spice of life!)… but if you find yourself in dire straits – a pulse and cereal can sustain you quite nicely. However, I think the goal should be to move beyond mere survival. We can do better, and with prudence we’ll continue to do better into the future. Pass the apple sauce, please.

    • The book will appear one of these fine days, I hope. But in the mean time I have lots of seeds to sow. So much work, these annuals!

      I want to hold on to your grain/legume point, and come back to it in more detail at some future point. Feel free to remind me.

      • “So much work, these annuals!”, he exclaims. And rightly so – for the laborer is worthy of his hire. Well, in theory anyway.

        Yes, reminders of legume/grain dietary complementation will be forthcoming. Tom is my sensei in this regard. 🙂

        • Eh, which Tom? I’m a spud man not a grain man but if you mean is it very important to mass produce carbs and protein to fill billions of people’s bellies then, yes I’m up there with you. And let us not forget that the spud is a perennial, at least in southern England, where it is fair to say it is a weed in my garden, popping up where it is not wanted.

          The statistical information is really useful here so the more humane amongst us can argue for realistic, ecological and just political choices. I reckon there are liars on both sides of the sustainable food debate.

          My own focus is an urban one but is essentially similar in the sense that I am thinking of land use that is human sized, that is manageable by human beings – obviously it can’t feed billions – but could significantly reduce the pressure on proper agriculture.

          I did watch a Geoff Lawton video with Mark Shepard in it and he came over pretty sensibly and humanely. He was also growing peppers in his alleys, so the penny might’ve dropped on the issue of annuals, unless his part of the states is warm enough to grow peppers perennially, which I dont think it is.

          Keep up the good work on the statistics

          • Hi Tom – yes I meant you. But in regard to making reminders for Chris so that he keeps a topic close to the top of the stack.

            And legumes for soil nitrogen should come close to concerns you’ve expressed here once or twice. Sure, I have a thing for soy – and you’re not convinced it has much utility in the U.K. But whether soy is the legume of choice or not, biologically fixed N is pretty neat. If one can have pulses to eat with their cereal (yielding a nutritionally balanced diet) and improve the nutrition in their garden soil for the same effort – then where’s the harm?

          • Tom, yes I think in our climate potatoes are a good way to go for gardeners & small scale farmers. And yep they’re perennial but I’m not sure how much that helps on ecological grounds at least on larger scales as you have to dig them out of the ground. They’re also short-lived and high nutrient demanders – classic ‘competitor’ plants as I’ll be discussing in my upcoming posts. So as you correctly point out, the main feature of their perenniality is a curse more than a blessing – weeds!

  2. PS, a load of people are busting the myth about not saving your own seed potatoes. Now I know replanting perennials resembles annual growing more than it does perennial polycultures but it has a lot of things going for it, regardless of blight – which has been addressed by the wonderful organic Sarpo potato which quite rightly has been flung in the face of the GM brigade.

  3. Clem, i’ve gone legume crazy. I wander around garden centres upturning pots looking for root nodules. I then buy things that are too big for my garden or break the rules of my allotment. Not all the legumes described by permaculture influences such as Martin Crawford seem to actually fix nitrogen in anyway I can see, so I actually have to see the plants roots for myself. It is an interesting journey though.

  4. Hi Chris, I love how in-depth this article goes! However, I think the case for perennial intercropping instead of corn is much stronger than the comparison you make here.

    First, there’s a good reason why only about 1% of American corn goes to directly feeding humans: It isn’t very good for us. For one, a lot of the calories in corn aren’t actually usable by our bodies: The amylose that comprises 25% of dent corn’s starch calories is only absorbed at about 50% efficiency, which means that corn’s calorie power is reduced by about 10%, to about 12.5 million calories per acre when used directly for human consumption. For another, the remaining starch, amylopectin, has been linked to metabolic syndrome. Corn’s moisture and fiber contents mean that it has a high glycemic load, which also spells metabolic trouble. It’s important to keep in mind that the civilizations that built themselves around corn were using a very different crop with very different nutritional characteristics and yields.

    It’s also worth pointing out that Shepard’s figures for perennial crops were highly understated. For instance, Shepard assumes only two bushels of apples per tree, when apple yields are likely far higher: Five or six bushels per tree is probably closer to typical. (We should probably compare average yield here, because the 13.9 million figure for corn comes from the average American yield, not low-end estimates.)This change alone revises Shepard’s estimate from 4.6 million calories to 5.9 million calories per acre. (Apple yields in the United States averaged 6.6 million calories per acre (248.6 million bushels on 328,000 acres), which should give an idea of how productive apples can be. Similarly, elevating his theorized chestnut yields from the rock-bottom (1,000 lbs per acre) to an in-the-middle figure (let’s say 3,000) adds another 2 million calories per acre, to 7.9 million. And that’s just for the fruit and nut crops.

    So, realistically, we’re looking at 7.9 million calories per acre (maybe more if we want to keep bumping up estimates for the other crops like currants and grapes) vs.12.5 million for American corn, the most productive industrial grain crop in the most industrially advanced country in the world. That’s assuming that all of those corn calories are going directly to feed people, which is impractical (and perhaps even dangerous) for the reasons mentioned above. Maybe when it comes to “feeding the planet”, perennial intercropping can compete with corn after all?

    • Thanks for commenting, Robert. You’re doubtless right about the limited direct edibility of the corn, but you haven’t yet convinced me to overhaul my general argument. I guess if we start looking at the digestibility of the corn, we’d have to do the same for the perennial crops – I don’t doubt that the latter would be relatively more digestible, but you can’t only revise the one figure. More importantly, I’m still suspicious of the yield figures. The animal ones are completely beyond the bounds of the realistic, while the fruit & nut ones… well, if Shepard has been developing his farm for 16 years but is still putting together data from published average yield figures to prove its superiority, I suspect there’s an underlying story that’s not being told. I’m not convinced that you can just take average conventionally-grown yield figures for top fruit, soft fruit, nuts etc, add them together, and infer a total polyculture figure accordingly. And if the US corn crop is too compromised a comparator, maybe you could take the UK wheat crop which turns out at at least 10 million calories per acre – still comfortably above Shepard’s figure. I’m not opposed to the general argument that it would be a good idea to shift focus from annual grain agriculture towards perennial fruit/nut polycultures, but I still think it’s misleading (and unnecessary) to claim that the latter outyield the former calorifically.

      • I love all of this analysis, Chris–I’m a newcomer to your work but not as much to the perennial polyculture world. Shepard’s doing a lot of great work but I agree that his book makes shaky claims. I’m a permaculture teacher and designer in Denver, so I’m all-in on this holistic food systems jazz, but denying the complexity and work involved is doing everyone a disservice in the long run like you say.

        I worked for two full growing seasons in a 30-year perennial polyculture at Bullocks’ Permaculture Homestead up on Orcas Island in Washington, and I can attest to the large amount of fiddly work in maintaining, managing, and harvesting in that system. It’s wonderful, enjoyable work, and not back-breaking like other agricultural forms, but it is pretty constant. Also, fruit tree yields go way down if they’re covered in vines or shaded by larger nut trees. And have you ever tried to harvest fruit or nuts that are falling into gooseberry bushes? Over time at the Bullocks’ place they’ve moved to a mixed-system model, with annual gardens in the lowlands, fruit and nut trees on the slopes, and lots of nooks and crannies fostering other perennials. I love this wording from above: “surely there will be tradeoffs between the degree of polyculture ‘mimicry’ and ease of harvesting”. In my experience yes, a thousand times yes.

        I’ve come to feel that there are no home runs, no silver bullets–and that’s kind of the point. Small-scale diversified solutions are what we see in the natural world, and it’s hubris to imagine that we can contradict that pattern indefinitely. I think Mollison did a lot of damage with sayings like “the designer becomes the recliner”, and it’s clear thinking and analysis like the above that will move us to the next important stage of evolution with these ideas and practices.

        • Creighton – thanks for that. I spent a couple of weeks at the Bullocks’ place in 2002. Very inspiring…and, yes, lots of work! Good to hear your voice on the issue of silver bullets – there’s plenty getting touted in mainstream ag, but alternative ag is far from immune. Seems like there’s a lot of denial around the basic truth that producing a livelihood takes work. But work isn’t always such a bad thing…

    • Hi Robert,
      Your argument about corn starches (amylose and amylopectin) not being all that desirable for our diets is interesting. You realize corn is not unique in storing energy in starch, right? And there is also the notion that not everything we consume has to have a nutrient contribution (see fiber).

      So the statement that corn isn’t very good for us makes me wonder: compared to what? I agree corn shouldn’t be the only food in the diet, but I think one goes too far in disparaging the crop in this manner.

      If you have a minute, could you point to some evidence for your contention: “For another, the remaining starch, amylopectin, has been linked to metabolic syndrome”. Thanks.

      • Hi Clem, I think fruits and nuts are typically nutritionally superior to grain crops. The human gut is just not set up in the same way as a true granivore’s: We lack a true cecum, in which dense starches could ferment for a long time. Instead, our physiology is most consistent with the fruit-based diet of our closest relatives in the Pan genus.

        Amylopectin has been found to induce irreversible insulin resistance in rats, and although human trials are hard to design, preliminary research seems to corroborate the idea. http://ajcn.nutrition.org/content/61/2/334.full.pdf+html

        I am aware that corn is not the only dietary source of starch. However, the modern corn that many people extol as a world-feeder contains more amylopectin starch as a percentage of its calories than pretty much any other foodstuff. So I think it’s worth staying skeptical about this miracle crop.

        It’s true that not everything we consume has to be a nutrient in the traditional sense. But people often tout corn’s calories per acre while glossing over the fact that many of those calories are uncontroversially unusable by the human body.

        • “Instead, our physiology is most consistent with the fruit-based diet of our closest relatives in the Pan genus.”

          Well, yes, but there is some adaptation since we shared Pan ancestor, and they eat meat as well. I think you are on with the starches, there are way too many, too much, in our diet. I was once on a completely no grain diet, lost quite a bit of weight just due to that fact alone, but the really eye opening moment was when I walked into a supermarket with my modest shopping list. I felt as though the isles were smothered by a giant wave of grain. Everywhere you looked. This was before the industry started to hide corn syrup.

        • Robert,
          Thanks for the link. And I will agree that fruit and nut contributions to our diet are quite valuable. I should also point out that I feel somewhat conflicted defending the dietary merits of corn (as a soybean person)… but I still feel I should push back some if Zea mays is going to be painted in too negative a light.

          Table 3 in the following article suggests to me there isn’t so drastic a difference in amylopectin content between some of the major starchy foods as you’ve suggested.

          And further, if you have a look at (esp. pg 44):


          The overall significance of Behall and Howe’s 1995 study is not so damning of amylopectin as it might seem on first blush. So we may still want to keep and eye on total starch (particularly low RS starches) the idea of tossing corn overboard seems imprudent to me on the face of the present evidence.

          But I am quite happy to suggest more legumes should be eaten…

          • Hi Clem, thanks for the engagement.

            I don’t think corn is unique in its unhealthfulness. You’re right to note that wheat and potatoes are probably about as bad. But because I advocate for more consumption of fruits and tree crops, these facts are actually consistent with my broader points.

            The best that researchers can say about amylopectin is that it doesn’t raise markers of metabolic disease higher than the nationwide baseline. But given the current epidemic of the disease, I don’t think that’s good enough. Consumption of fruits and nuts has been linked in many studies to improved metabolic outcomes. I think this evidence is enough to support a claim that fruits are significantly more nutritious than grains. Once that premise is admitted, it makes sense to question whether grain should be considered our nutritional savior.

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  6. Interesting review of Shepard’s book and interesting discussion in the comments, but the biggest questions I would have aren’t on the production side, or if they are, they’re more sociological than agricultural.

    For example, how can a perennial agriculture of the sort Shepard apparently describes make any sense apart from multi-generational family farms? Surely these complex systems won’t withstand being bought and sold on the market with every new generation. Are parents (especially aspiring revolutionaries like Shepard) going to stop telling their children to “follow their dreams,” that they can “be whatever they want to be,” sending them to college (and even high schools) that prepare them for anything but fidelity to their home places and their parents’ values and, perhaps even more significant, instill in them notions of success that are all about material comfort, money, and status?

    On the consumer side, where is the demand for all these chestnuts going to come from? Of all the people I’ve met and read about that love to talk about permaculture(TM) and perennial polycultures (and sometimes even farm in those ways), I don’t know any whose diet evidences a real belief in those ways of farming. Does Shepard’s agricultural footprint and caloric intake not consist largely of bread and/or pasta, rice, potatoes, grain-fed animal products… (together with plenty of annual vegetables)? I like eating chestnuts, but besides the fact that they’re highly perishable, even compared to other nuts, let alone grains (and therefore normally just a seasonal food as opposed to a year round staple), and have a per calorie price tag consistent with their proper place in the produce department, they’re also very time-consuming to prepare and shell. Even apart from the price, it makes sense to me that they’re mostly a specialty snack food instead of a staple energy source.

    And given that chestnuts are currently a specialty snack food, how are farms going to market them? Can Shepard justify selling them at commodity prices? Could he even access commodity markets from his location? If he tries to direct market the chestnuts, how many can he sell selling them as a specialty snack food? Even if he could somehow sell as many as his farm model would indicate, wouldn’t he likely saturate the market for the nearest 100,000+ people? How many acres of conventional corn would be displaced at that rate? If he aspires (and his calculations clearly indicate he does) to displace conventional farming methods, what’s going to motivate the necessary changes on the consumer side? If he hasn’t been motivated to radically change his own diet, then he surely won’t be able to convince consumers to do so.

    • Eric, thanks for your comment – many thought-provoking questions there that I’d like to respond to. But I can’t right now due to other pressures. I’ll try to come back to them in some future posts.

  7. Thanks for this analysis. I do wonder about a few things.

    First is the level of inputs that an acre of corn needs “off site” when it is not fed by oil or mining based fertilizers vs the inputs needed by perennial systems. I would assume that they are higher, and the size of “ghost acreage” will be much higher for corn production.

    The next thing is seed input. Most perennials don’t need seed input and can be cloned with parts of the plant that often need to be trimmed anyway. While corn needs a lot of seed to be able to grow the next year. I do not know the ratio of corn seeds needed vs the amount harvested, but it is a factor to consider.

    Also, in perennial systems you can use fast growing pioneers that have multiple added benefits, but in the end also produce bio fuel. There are strides being made to actually make quality bio fuel from cellulose/lignin splitting systems, but in the meantime we can heat our homes with it (and steam powered trains :)), or generate electricity.

    Then you have multiple opportunities for agro forestry systems that are not taken in to account. Biodiversity and integration of nature in agriculture being one.

    I like your critical take on the matter, and will continue to follow your writings as they have peaked my interest.


    • Thanks for commenting, Michel. Interesting points, but I’m not entirely sure. Suppose you grew corn in an organic rotation – does it have more ‘ghost’ inputs than a perennial polyculture? Maybe, but I’m not yet convinced. You’re right that seed input is an issue. But then again, high nutrient return perennials are quite short-lived, and indeed are often cultivated as annuals, and the cloned matter required to establish them on a large scale is significant – often more than annual seed input, eg. potatoes. And annuals can also have multiple uses, including as biofuels.

      I agree with you that perennial polycultures probably have biodiversity benefits and there are many good reasons to plant them and to experiment with them. All I’m really saying here is let us not over-sell their macronutrient productivity vis-a-vis annuals.

    • Michel:
      On the matter of seed requirements for corn – it might be less than you imagine. You are right that as a seed sown annual you do have to first have corn seed production. Exact resource allocation for seed production will be context sensitive – are we raising open pollinated corn or hybrid corn? With open pollinated corn there is no special seed production technique – raise a healthy crop and keep some of the seed for next year. A reasonable seeding rate for corn in the US Midwest is 30,000 seed per acre. Seed size for corn varies, but if we use a value of 2,000 seed per pound and realize that a standard bushel of corn weighs 56 pounds then we get 112,000 seed per bushel – enough to plant 3.7 acres next year. A reasonable yield expectation for open pollinated corn (again, US Midwest) might be 120 bushels per acre (conventional production using fertilizers and pesticides) so that a single acre of seed production can theoretically provide about 450 acres worth of seed for the following season. Looked at another way – to produce enough seed to replant a single acre next year one would keep back 15 lbs of seed (30,000/2,000) which is about a fourth of a bushel (0.26 bu), or about 0.2% of the acre’s total seed production. So yes, there is a seed production requirement. But two tenths of one per cent of your production doesn’t seem to me too onerous a price.

      I can do the same for hybrid seed production if anyone cares. The take away is much the same – seed production does have a cost, but the productivity of corn easily makes up for it. Wheat and soybean seed production costs vs. their respective productivities are less favorable when compared with corn.

        • Well, potatoes are for all intents and purposes annuals in our climate. The fact remains that corn needs fertilizer. Or if you plant to use ground covers for nitrogen fixing, this also means the average production per acre goes down by 25% if you do it every 4th year.

          Also, I think it would be fair to say that a diverse agro forestry system has a lot more to offer in terms of nutrition than a field of corn. A friend of mine had a student make an analysis confirming you could live off of a typical food forest system nutritionally. If you factor this in, it would be fair to compare a food forest system with an annual system that delivers the same nutritional profile.

          • Your point about delivering a comparable nutritional profile is most appropriate. We’ve discussed this to some extent here in the past. Pulses like beans, lentils, peas, etc compliment the cereal grains (counting corn among the cereal grains for this discussion) quite well in a human diet. As legumes the pulses also fix nitrogen. Supplementing a simple pulse/cereal rotation with a kitchen garden of veges can make for a very nice nutritionally complete diet.

          • Yes, most of the starchy perennials grown as staples in the human diet are treated as annuals or not far off – which tells its own story about productivity…

            You’re right that corn needs fertilizer, but even if you factor in 25% for ground cover and Clem’s 0.2% for seed its calorific productivity still greatly outstrips Shepard’s figure (wheat might be a better comparison, where the difference would be narrower, but still quite large I think). Most high-productivity commercial perennial systems also use fertilizer from outside the system. As I mention above, I’m not convinced that an endogenous system of the kind Shepard describes can be as productive as he claims.

            But you’re certainly right that diverse agroforestry provides a better overall nutritional profile, and that a better comparison would be with a more mixed annual system. I might try such a comparison – here I was merely following through on Shepard’s own comparison between his chosen agroforestry system and a field of corn. I don’t need persuading that an agroforestry system can be more nutritionally complete and less environmentally damaging than the average cornfield. But I do need persuading that it’s more calorifically productive relative to labour or area, even when you factor other relevant inputs like fertilizer.

    • I get around 700 corn seeds per ear and each plant grows an average of 4 ears. So I can save 2,400 seeds from one single plant.

      Very few perennial vegetables (other than Jerusalem artichokes) can increase numbers by 2,400 per plant unless using tissue culture.

      I am not saying that perennial polycultures do not have their place, I have a perennial polyculture, but I also grow many annuals and save their seeds each year.

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