Soils ain’t just soils – and compost isn’t just compost

Sorry for the long gap between posts.  I’ve mostly been off touring around national parks and permaculture places in northern New South Wales and southern central and southeastern Queensland with my daughter.  Some great walks in spectacular country, and some interesting comparisons between different permaculture demonstration sites.

Not long after we got back I discovered the great blog Living at Gully Grove via a guest post that its author, Chris, wrote on Farmer Liz’s Eight Acres blog about how their family uses permaculture.

When I clicked across to Living at Gully Grove, I found to my delight that, like us, they live in the hilly margins of the Lockyer Valley and clearly face some of the same issues.  It’s always great to find someone who lives in your region who is willing to share their knowledge.

That happy discovery led to an exchange of views via comments on Chris’ blog and the start of a “conversation” about sandstone soils.  As you may know if you’ve been following this blog, our place is steep sandstone country, with many rock outcrops and soil that is made up of sandstone in various stages of decomposition, and generally not more than 60-70 cm deep.  Even that shallow layer of “soil” often has at least half its volume made up of gravel and small rocks.

What passes for soil on a sandstone ridge

What passes for soil on a sandstone ridge

Early on we recognised that one of our main food production challenges was going to be the need to create suitable soil.  To that end we have done all kinds of things, including sieving the rocks and gravel out of huge quantities of the native “soil”, green manuring, mulching, terracing, etc.

So when Chris said:

Have you ever let a garden bed go (ran out of time to keep up to it) and noticed the good soil revert to something like dry potting mix?

The hardest challenge for us hasn’t been building the soil, but rather maintaining it. I notice where we have swales, the soil doesn’t need much of our attention, except where it crosses a sandstone shelf. It only takes a season of hot dry weather, to cook any good soils we don’t maintain.

I knew exactly what she meant.

For us, the challenge hasn’t only been to create good quality soil (and I can’t claim to have satisfactorily cracked that one), but to keep it in good condition.  An apparently well prepared garden bed can start the growing season with lovely fluffy, moist soil that holds together exactly right when squeezed in the hand and produces a good crop.  Then, unless it is constantly maintained, a few months later it is dry, loose and apparently lifeless.  Chris’ description of “dry potting mix” soil hits the nail on the head, particularly if one interprets it as the crap bagged potting mix that supermarkets and garden supply places sell. The plant material in these mixes is generally at best only partly broken down, and there is no evidence that there is, or ever was, life in them.

I’m no expert on soil processes, but I suspect that the coarse material in our “dry potting mix” soils is compost “residue” that has not been broken down. This is probably because (a) the soil was not sufficiently healthy initially, and in particular did not contain sufficient humic matter and soil organisms; (b) when we let the bed go there isn’t sufficient ongoing moisture in the system for biological processes to continue creating and maintaining humic matter; (c) if there isn’t a continuous cover of thick (but air and water permeable) mulch then soil temperatures rise and water content decreases; and, on a sandstone base, there is likely to be significant leaching of nutrients when major rainfall events occur. I have to say though that I have had this problem in some beds that I was actively managing, not just in ones that I’d been ignoring for a few months, but that may have been due to the leaching mentioned in the last point above.

Does the above explanation seem to match your experience / observations?

My way of tackling this problem is still evolving, but it includes:
# keeping a fluffy straw mulch cover on the soil that allows air and water to penetrate, and at the same time significantly reduces drying and insulates from overheating;
# adding green manure to the soil and digging it in. This isn’t the usual “green crop dug in” approach, but a mix of moist and drier (but still living) plant material put through the chipper / mulcher sufficient to make a 25-50mm layer on the surface, then watering it and digging it in;
# adding sieved compost “fines” (containing the humic material) to the soil;
# adding dry horse manure that has been put through the chipper / mulcher to the surface layer.  Processing it this way produces a fine, light fluffy material that holds moisture and gives the soil a great “texture”; and
# to the extent that our water supply allows (we have only tank water), keeping the soil moist, even when the area is not in production.

Good compost of course contains humic material, but can also contain a lot of woody material if you use coarse chip mulch as part of your carbon source.  This is part of the reason it’s a good idea to sieve your compost and put the finer, humic, fraction into the soil, reserving the coarser material for mulch or for feeding the next batch of compost. Unless you already have a healthy soil, there’s not a lot of point in incorporating coarse, only partly broken down, compost material into it.

If you want a good guide to how soil “works” and how to maintain its health, the best book I’ve come across is Toby Hemenway’s Gaia’s Garden (Chapter 4: Bringing Soil to Life). This is by far the best and most practical permaculture text I know. The other good source for soil matters is, perhaps surprisingly, Harvey Ussery’s The Small-scale Poultry Flock (pages 137-144 for soil matters). We have a pretty comprehensive permaculture / organic library but these are the two books I go to first when I have a question, and I seldom need to go past them.

6 thoughts on “Soils ain’t just soils – and compost isn’t just compost

  1. PS, I also noticed that the humble Kent or JAP pumpkin was able to do the same exploitation of soil niches, on a sandstone shelf. It finds the moisture and nutrients all on its own, and will help shade the ground in summer. So long as the pumpkin can put down roots in a shady, moist niche, it can survive the dry times. Just some ideas if your pumpkins are taking over your nice veg patch and you want to put them some place out of the way. We grew our best pumpkins on sandstone shelves and they never got in the way, because nothing else (edible) would grow there.

    • Funny you should mention pumpkins in this context Crhis. I’ve been thinking about the very same thing for a couple of months. Actually my zucchini failure this last summer got it started. I was pondering why they grew and flowered so extravagantly but then produced only small fruit and got the worst crop of downy mildew I’ve ever had. Normally I expect this when the wet season really gets going, but we’ve had no wet season this year.

      Then I noticed that the pumpkins (only about five metres away) were doing really well, no mildew and large healthy fruit. I’ve put it down to an excess of nitrogen in the zucchini bed (it was “refurbished” at the beginning of summer, and probably had way too much nitrogen – hence the initial lush growth. The JAP pumpkins on the other hand were “volunteers (we never intentionally plant pumpkins). One was growing at the edge of the dripline of a lime tree. We are very careful about how we manage our citrus, and particularly how and when we fertilize, so there was unlikely to be much “added” nutrient getting to it. The other pumpkin was growing from a totally unprepped area in some sandstone fill that had been dumped during the excavation of our foundations. It has been the same in previous years and, now that I think back, perhaps more clear that they grew well in the unprepared sandstone areas, providing they had enough water. Memo to self: when the food forest is going, plant pumpkins in more natural areas between the swales and not on the berms (which will be mulched and composted). Thanks for the confirmation.

      • Our area just loves JAP pumpkins, which I found very interesting I must say. We can grow pumpkins and sweet potato like weeds, because they actually prefer less nutrient input. The moisture is what they cannot do without though. I noticed when our pumpkins went travelling (they’re all volunteers too) they would look for the moisture niches near plants that would shade their roots, while allowing their tendrils to expand even further into the sunlight. If you want to know how moisture is present in your soils, plant a pumpkin and see where their roots end up putting down.

        Interesting that you had a comparison going with the zucchini. Your story perhaps showed me why our pumpkins thrived on the “cut” side of our house site, and not the “fill” side. All lush growth with very little happening in the way of fruit, but we had so many pumpkins on the degraded side, we had to give it away to anyone who would say yes.

        Plants can speak, we just have to relearn how to listen.

  2. I’m really glad you’re talking about this, as I’m nodding my head all the way. I think your strategies are sound, but also comprehend the extensive labour involved too. From a permaculture perspective, the natural question becomes, how do we get nature to do most of the work for us?

    Watching some Geoff Lawton videos recently, and greening the desert, the main strategy for building topsoil is by finding the right ground-cover plants to grow, to capture nutrients via wind and water. He also had some legume type trees planted for chop and drop. I’ve noticed the pigeon peas we can grow in our area, constitutes as legume and they drop leaves naturally in a drought.

    I’m wondering if you have a piece of soil you want to improve on a slope, if you plant a row of pigeon pea trees at the very top – that will attract birds, reptiles and mammals to the area, leaving their soil building droppings too. Then directly underneath the trees, plant a hardy groundcover – I’ve found that myoporum parvifolium or creeping boobillia does well on sandstone. It seeks out the niches of soil it can grow in and eventually covers a rocky outcrop. The benefit is, the leaves capture debris and eventually starts developing a layer of soil on the sandstone.

    I’ve only noticed this recently, after looking at some creeping boobillia I planted a few years ago. Nothing would grow in that area and where I planted the boobillia, I thought it would go no further – stopped by the sandstone. But it’s successfully crept down the slope and built soil over time, so it can put down more roots and travel further. The answer is always in nature it seems, we just have to keep experimenting. :)

    • Thanks Chris – I love thoughtful comments. I completely support the principle of having nature (or some other component of the system, e.g. chooks) do the work in building soils if this is possible in the circumstances.

      However, with regard to Geoff Lawton’s videos I do have to say that, having spent 25 years working in developing countries on natural resource management, I’ve become highly suspicious of self-reported case studies. I’d love to go and do my own evaluation of his projects that he makes videos about, but of course lack the resources. As the next best thing, in the last two months my daughter and I did tours of three permaculture demonstration properties (Zaytuna, Djambung Gardens and Maungareeda). We were underwhelmed by Zaytuna, in terms of food production per unit effort or per unit area, or as a convincing demonstration of permaculture principles. This is definitely not to say that my confidence in permaculture was shaken, far from it.

      Anyway, back to your main topic. I very much agree with you that getting a ground cover going, and preferably a legume, will improve the soil. In fact the key may not be so much the “ground cover” (in the sense of a low-growing plant) but a low closed canopy that creates a microclimate underneath that prevents drying by sun and wind. From that perspective, dense plantings of pigeon pea should work. However I think we need to make sure that the substrate is kept moist so that the decomposers and other soil-building organisms are working at maximum efficiency. And if the planting has some other function to contribute (windbreak, shading out hot western sun, food, mulch, etc.) so much the better. To my mind pigeon pea ticks all of these boxes in our area. Do you harvest the “peas”? When fresh they make a great addition to stir fry, and when mature they are equivalent to mung beans for making dahl etc., and if you are really keen, can be ground up to make an Indian savoury cake called idli.

      I’m planning on using pigeon peas in this way on the southern and western boundaries of the food forest, in combination with lemon grass and possibly cassava (I’ve just started an experimental planting of cassava), but after your suggestion I’m going to try the pigeon peas in planned “future use” areas.

      About chop-and-drop, have you come across the guideline that this should be done only in periods when precipitation is in excess of evaporation? Since evaporation exceeds precipitation for most of the year (all of the year sometimes) in the Lockyer, there seems to be a real question as to the usefulness of c&d here. I only came across this guideline (via Tom Kendall, from Maungareeda) after I’d been trying to answer the question as to whether c&d straight onto the surface would lead to a loss of nitrogen to the atmosphere as the material dried out – in which case it would be better to drop it under a mulch layer, so that the decomposers would do their work before it dried out. I can’t find anyone who has the technical knowledge to answer this, but have adopted the practice anyway, on the basis that it is logical and seems to get around the need to observe the abovementioned guideline. If you or any reader can provide an authoritative answer to this question I’d be very grateful.

      I totally agree that we just have to keep experimenting – that’s part of the joy of using permaculture principles.

      • I love watching anything to do with permaculture (sites in particular ie: greening the desert) because they often have gems of advice which can really make a difference. But I also recognise they have A LOT of inputs the regular gardener/landowner wouldn’t have available either. It’s interesting what you mention about Zaytuna. I’m wondering if the drought has anything to do with the issues you raised? Our garden was pretty miserable this summer and only started coming into its own with the cooler weather of autumn.

        Actually, that aligns with what you said about chop-and-drop. I’ve noticed the best results I get is when it’s done in autumn. The temps drop so plants don’t struggle in survival mode, and the microbes seem happier to break down the material closer to the surface, where it’s dropped. Because the ground still gets warm during the day, when the cooler temps of night arrive, transpiration occurs, causing moisture to remain present longer. I only chop and drop where I have plants growing, as it stops the material drying out quickly. Something about autumn kicks the garden into a new zeal before the winter arrives to shut everything down.

        You mentioned the importance of persistent moisture on sandstone soils and that’s the ticket to success. We struggle with that aspect too. Without moisture, anything we endeavour to improve will be dried up in the next heatwave. That’s why we found swales work, even though we probably don’t plant them thickly enough, so it takes several seasons for them to mature. I’m thinking anything which can grow grass could put a mob of kangaroos to work. We notice they love our swales because it grows sweet, tender grass. The mums always bring their joeys for a feed (and drink when rain is present) at our swales. They’re not spectacular swales, in fact you probably wouldn’t notice them unless I pointed them out – but they’re an improvement on the perfect drainage of slopes we had beforehand.

        Regarding pigeon peas, I used them to make a salad once, and the chickens don’t mind me dropping them pods either. We’ve even used them dried to help our daughter with learning counting and sums. No problems putting them through the chipper either, and they break down so easily. They’re one useful plant! In fact, I’d even be so bold to suggest, we’d still be living in a dust pile if it weren’t for the humble pigeon pea. Where they grow, they attract life to cycle.

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