Building and maintaining soil fertility: utilizing the decay cycle to increase the velocity of nutrients accumulation

For most of us, the biggest barrier to successfully growing our own food and medicine is a lack of nutrients in the soil we have available. Key to having productive and healthy gardens is having healthy living soil. I spent a lot of my early gardening years trying to grow in depleted soils, and as such created a lot more work and had drastically reduced harvests. Soil degradation has been a serious issue over a lot of the arable land of this planet, particularly farmland. Decades upon decades of plowing and monocropping has left much of the breadbasket of North America depleted of just about any soil fertility, and this insanely destructive method has also drained the ancient aquifers in much of those regions. The only major change we’ve experienced in farming since the apocalyptic Dustbowl of nearly one hundred years ago is that synthetic fertilizers became extremely common, allowing farmers to grow vibrant crops on depleted soil. We’ve been approaching a peak in soil, oil, and phosphorous for a long time and nothing substantive has been done to deal with any of these problems.

As a parallel to the depletion of farmlands, the soil where most of us live devoid of much organic material and adequate soil life due to decades of the obsession with lawns and lawn cleanup habits that involve removing biomass and spraying poisons.

My goal with this piece is to both supply beginning gardeners with some simple ways to build up the soil in their gardens while also moving beginners to a deeper, less reductionist understanding of soil and system fertility. As we move beyond a simplistic and mechanistic understanding of gardens and view the relational aspects between elements of a garden or farm system, we can make sustenance and cultivation decisions informed by a wider view of ecology and our place in it, not to mention harvest greater products, both in terms of quality and quantity.

If we are to design the most robust and productive (not to mention ecologically appropriate) farm ecosystems, centering them around woody perennials like trees and bushes is a good way to ensure long term soil fertility, to say nothing of the benefits of tree crops themselves. Even if you’re not engaging in such a large and ambitious project, using tree leaves as a source of coarse biomass rich in minerals is typically achievable. Many of us can go around gathering up bags of leaves being tossed away in the autumn, and maybe even have people looking to get rid of leaves bring them to you themseles. If you’re fortunate, you have leaf and yardwaste piles that have broken down into rich compost. Some of the best soil I’ve used for starting seeds and helping plants set down some deep roots was dug from under a neighbor’s leaf pile (which just happened to also have occasional white truffles growing in it, since the tree that the pile was under had formed a symbiotic relationship with the fungus).

Because trees and other established perennials often reach deep for minerals and nutrients and bring them above ground, they’re ideal for building fertility. Leaves vary by species and time of year, but as a whole the fall leaves many of us have access to are higher in carbon than nitrogen, making them good for layering between food scraps in compost piles or acting as bedding or ground over in livestock shelter. Only a few species cause a problem to plants when used as a mulch, such as walnut trees. On the flip side, some trees and bushes are particuarly good, especially ones that fix nitrogen like autumn berry and locust trees. We make ample use of the former, and hopefully we can transplant some of the latter in soon.

Eleagnus umbellata grows a lot of biomass in the form of wood and leaves, not to mention a delicious and nutritious fruit. Just don’t let them get out of hand.

Aside from layering them as part of a composting process, leaves can be used as a mulch layer in garden beds, either whole or shredded. Shredding means they’ll break down faster and are less likely to mat down in less desirable ways, but of course requires some time and energy (unless!….more on that later). Whether and however much you decide to shred leaf mulch, it works to protect the soil while enriching it, much as any mulch layer, and as such allows microbes, fungi, and soil animals to thrive and keep your soil fertile and alive. Even composted on their own, leaves create a great compost to amend just about any garden soil.

Hay, straw, and grass clippings can likewise be used to build soil fertility, both as mulch and in composts, but I don’t find them quite as good of a source of nutrients. Straw is carbon rich, the other two fairly high in nitrogen. If you have a lawn you mow and it’s got a diversity of plants in addition to grass, and you don’t have any herbicides in it, it’ll make a decent source of nutrients. But herbicide and other pesticide residues in any of these grass crops could cause big problems for a vegetable garden and even some perennial plantings, so while all can be used as mulches and hay in particular does a good job for deep mulch techniques like that used and popularized by Ruth Stout it’s absolutely important to make sure it has no herbicides. Personally, I won’t use straw as a top layer of mulch any more after some severe slug issues, but plenty of people swear by it. Maybe if it were shredded like I do with leaves, as that reduces air pockets that slugs like.

Wood chips are very high in carbon and are hard and often large pieces, and thus will take significantly longer than these other biomass sources to break down if used as mulch, but they’ll do so eventually and will absolutely enrich your soil and help it retain moisture. Many swear by “arborist chips”, which generally include some shredded leaf matter. They’re also ideal for growing and harboring many types of fungal mycelium, particularly hardwood chips. In fact, while many gardeners wouldn’t think of mulching the PATHS in their gardens as a way to build fertility, the action of wood chips growing fungal mycelium in them and in the soil beneath it encourages soil life throughout the garden as well, on top of keeping moisture in the area.

Aside from trees and bushes, as well as grasses, some common herbaceous perennials act as nutrient accumulators as well. Plants like comfrey and nettles are used often to build up nutrients to use as fertilizer or even as animal feed. We use comfrey frequently to supplement the diet of the laying hens, and both work well as a primary ingredient in liquid fertilizers one can make at home. They can also be used for “chop and drop”, i.e. used as freshly cut mulch.

Stinging nettle, Urtica dioica
Comfrey, Symphytum officinale

In the same vein as these biomass perennials that we can enrich the soil in an unused area by planting cover crops. Plenty of annual and biennial species are cultivated to create more biomass in the soil and draw up minerals from below. These often include combinations of nitrogen fixing plants like legumes and long root vegetables to loosen any soil. Quick growing grasses are also often utilized. In many cases, these cover crops are often chopped and dropped or turned back into the soil.

For many of these perennial plant species, regular cutting or pruning can stimulate more robust growth, in addition to facilitating better fruiting in the case of a lot of fruit trees. For non-woody perennials like comfrey, cutting can be done monthly or sometimes weekly. In the case of trees and shrubs that are coppiced or pollarded (that is, new growth is cut periodically when the tree has recovered) the cutting is done in intervals of several years, species depe

There are two main sources I utilize for liquid fertilizers in my gardens, and they’re both kind of gross. The first is “compost tea” which is nothing more than weeds and other plant material left to rot and ferment in a bucket of water. There are some plants that are particularly good for this, such as comfrey, nettle, and alfalfa. These are the plants that likely also make good mulch or additions to compost piles because of their habit of accumulating a lot of nutrients. Comfrey heavy batches I find tend to get pretty funky rather quickly, probably because of its relatively high protein content, as will batches heavy in nettles and alfalfa (and probably other herbaceous plants that make a lot of nitrogen in their leaves).  Even without these particular plants, you can create a nutritious solution for your garden soil by harvesting weeds or just wild plants from the area, being sure to avoid too many seeds, and soak them in a bucket of water.

After a few days of fermenting outdoors, this smelly mixture can be watered directly on to garden beds to feed the plants growing there, as well as the soil microbes. If you’ve got some molasses around, it can be used to really kickstart the microbes in some compost tea, just as it does in compost.

Another source of quick nutrients for either plants or compost bins is your own urine. Urine is relatively high in nitrogen, along with a decent amount of potassium and magnesium and a bit of phosphorous. Agricultural research suggests that one person’s urine can be used to grow between 50% and 100% of the food necessary to feed them, though I wonder what factors would influence it; for example, eating more protein should increase the nitrogen content of someone’s urine, so theoretically a person whose diet is lower in vegetables and higher in animal protein would be producing more of the nitrogen necessary to feed them. I dunno, I’m a garden nerd not a scientist.

Assuming no infections are present, urine is a pretty clean liquid in terms of microbes. Because it’s a bodily waste many people assume it to be rife with the same sort of bacteria in feces that can make us sick, but in fact it generally has no more than what’s on reasonably clean skin (feces should also be composted into usable soil, but I don’t have enough experience to feel comfortable writing about it). If you’re still a bit squicked out by it, though, feel free to keep its application restricted to the compost bin or woody perennials. That’s mostly what I do. Care should also be taken if you’re currently using any strong antibiotics; I’m not sure which ones might come out partially in urine, but many can have dramatically bad effects on soil life so it’s probably best not to risk it.

Because of the high nitrogen content, continually watering with straight urine can quickly burn a plant and even kill it. For most garden plants applications of urine should be diluted with water at a 1:8 ratio. Some heavy feeding plants like tomatoes can tolerate a bit more, maybe 1:4. Maize can often take up to half urine as a regular fertilizer.

As I said above, it’s useful as an addition to compost, and in particular it can help to get a compost bin to the correct ratio of carbon to nitrogen to initiate hot composting.

Composting is the most important technique that everyone needs to know to build soil. There’s a number of ways to compost and generally the most important aspect of it is preventing pests, particularly those that can be disease vectors. Having a big open pile of vegetable scraps will probably break down eventually, provided rats and seagulls and such don’t just carry most of it away. It’ll also stink, something I think most people (and their neighbors) want to avoid.

Our enclosed bins. Nothing fancy, aside from the tomato plants growing out the side.

Generally it’s a good idea to enclose your compost, at the very least to keep it all in one place. I’m a fan of the sixty something gallon sized black plastic compost bins with access hatches in the bottom to dig out some finished compost before the stuff on top is done. In a pinch, you can attach four pallets together to make an open topped bin to throw everything in. This doesn’t necessarily keep out pests, but it helps somewhat.

Composting best practices usually involve some degree of calculation to get the ideal carbon to nitrogen ratio to instigate microbial breakdown of the materials and achieve hot composting. To get this to work, a C:N ratio of 30:1 (give or take a bit) is necessary as well as keeping the material moist but not soaked. Too much moisture and a pile can become anaerobic and thus suffocate the microbes that create the heat while breaking things down. While it can be useful to keep track of the C:N ratio of the things you put in and estimate for the compost pile as a whole, most people just layer some “brown” material (heavily carbon) on top of the “green” material (heavily nitrogen) each time they put stuff in, or when they’ve made a new layer. By alternating these green and brown layers, you’re pretty likely to get plenty of microbial and bug activity. It’s also one of the most important things to do to keep down smells and avoid attracting pests.

Mostly finished compost at the bottom of one bin.

Although it’s not necessary to turn a compost pile, it helps to maintain the decomposition process and produce usable compost faster as a result. The microbes that do a lot of the initial decomposition require oxygen. In particular fungi benefit from being well aerated. Many people will use a large turning fork to turn compost, but I’ve come to prefer using a corkscrew shaped aerator that you turn into the compost to dig it down into the pile, then pull upwards to pull the lower material up to the top. This is more convenient for the tall compost bins. If you can invest in a tumbling composter, which resembles a big drum up on four legs with a crank to rotate it, you can turn the compost simply by rotating the drum. Theoretically these can turn coarse material and kitchen scraps into compost in just a few weeks.

In situ composting, that is directly burying food scraps and other compostables into your garden bed without composting first, is just as useful provided that you don’t have a lot of pests that will dig up the garden space to get to your deposit. This method obviously doesn’t allow for regular turning, but you start getting the benefit of the added nutrients immediately.

Most guides to composting give some rules as to what you can put in the compost bin, and we’re going to break them. We’re not going to just ignore them as if they make no sense, but we’ll understand the reasons for them and make the decision to expand our composting beyond the usual prescribed materials. For instance, most people say not to compost any meat or fat, or any animal products besides eggshells. However, these things will definitely break down and even do a great job of enriching your soil. They’re just also more likely to attract pests who may dig into your compost. As such, enclosed bins are recommended for composting these materials, as is achieving hot, microbially driven composting.

This year I’ve been using excess eggs as a fertilizer for many of my nightshade family plants, particularly the potatoes and tomatoes, just by cracking one into the hole and covering with soil before putting the plant in. I’ve also buried eggs and a dead songbird I found underneath the winter squash, and a dead squirrel I found went into one of the compost bins to make some beautiful soil.

Animal protein is full of nitrogen and other nutrients, and as long as you can keep scavengers from digging them out those nutrients will feed your soil. I think most of us learned in school about indigenous farmers using fish as fertilizer for maize; I had some discounted fish pellets I was giving my chickens as a treat, which I ended up using as a fertilizer as well. This seemed to do a better job of avoiding animals burrowing into beds to dig up fish, a problem I’ve had before when trying to use pan fish. Alternatively, meat can be turned into maggots for consumption by poultry, thus turning it into manure to be put in the soil later (and reducing/helping to eliminate the need for purchased poultry food).

Utilizing manures is a classic way to build soil but I think is less feasible for a lot of us to use widely. Most of us don’t have ready access to a lot animal droppings unless we raise animals (which I totally do recommend on at least a small scale). In general manures need composting to be used in the garden with the exception of rabbit droppings (supposedly), both for the purposes of removing potentially harmful microbes as well as to create a balanced compost that won’t burn your plants with too much nitrogen. Poultry manure in particular is VERY high in nitrogen, and needs to be mixed with a lot of carbon rich material like wood chips/shavings, straw, or leaves. Luckily, if a flock of chickens has a large enough run you can get them to do a lot of the turning of the manure in with the carbon materials themselves just by layering them on the ground and letting their natural behavior of scratching for bugs and seeds provide the turning.

Speaking of raising animals, this is definitely one of the ways to increase fertility on a farm ecosystem. If you can raise animals, it’s definitely worth the initial and ongoing costs. The typical, reductionist assumption is that raising animals would be a drain on a farm ecosystem as they require food and water, but even if one were feeding animals entirely off of what is growing in a given space, the actions of a small herd, flock, or “flerd” can contribute to cycling the nutrients more quickly in the system and thus increasing overall fertility and production. By accelerating the decay cycle through either consumption and defecation or through mechanical motion in their normal behavior (i.e. getting them to turn compost for you by doing what they naturally do to stay happy), animals like chickens and even pigs and small ruminants encourage more organisms in the soil and better nutrient availability for plants and fungi, thus improving growth  Therefore, integrated systems in fact gain fertility by including some animals.

Our hens seem to really enjoy hanging out underneath this cluster of autumn berry trees.

There’s especially significant gains in fertility and overall production when animals that consume different food sources in a landscape are grazed in the same space, either in succession or together. If you have one animal that can digest coarse cellulose come through and clear that while fertilizing, and then another animal that needs lush greens comes through to find the improved fodder fertilized by the previous animal, and then clears the tall grasses and fertilize so the NEXT animal can get at the low growing stuff or scratch for seeds and bugs and aerate the soil in the process, each has made that pasture produce more for the next animal.

It’s kind of like the velocity of money thing; a dollar given to someone who will spend it gets a lot more use and stimulates economies more than a money hoarding billionaire having that same dollar. If you give money to an average worker, they can pay bills and buy groceries, which moves money to other workers who will spend it, etc. The same money generates more economic activity when used, just as nutrient accumulation and overall production increase if successions of organisms are available to move it along. Animals and fungi are particularly good at facilitating this acceleration and both are necessary to achive peak fertility in a system.

There’s certainly a limit to how many animals any given ecosystem can support, a point at which returns are diminished and the actions of the animals can be overall a degredation. But below that limit, animals that are the correct fit for the biome are a benefit to it, not a drain. And what that limit is is dictated by the fertility of the site moreso than any static number based on space alone. Figuring out how many animals are appropriate can be a little bit fiddly so I tend to err on the side of keeping a smaller amount and scaling up as seems appropriate. It could be that an intentionally managed system can increase that capacity down the line; in fact, that’s probably the goal for most of us.

Wine cap/garden giant mushroom (Stropharia regosoannulata) growing next to our turnips.

Likewise, introducing specific fungi to farm ecosystems can produce crops (mushrooms that are food and/or medicine) will increase the overall fertility and production. The two main actions we’re looking at here are saprophytic, fungi that directly feed on dead organic matter, and mycorrhizal, fungi that cooperate with specific plants to the benefit of both. The former’s role in creating fertility is obvious: breaking down mulches and other organic matter into usable soil while producing a crop. Fungi are often called the “teeth of the forest”. The latter is more indirect, but by increasing the growth of, say, woody perennials like trees which “mine” minerals from the subsoil and that we get literal tons of biomass from yearly in the form of leaves, we see that we pretty clearly have relationships in which outputs are increased simply by virtue of these relationships.

These relationships can also exist without the fungal species involved producing any crop for us, but since so many of those that do produce edible mushrooms are also great decomposers and companions to garden and food forest plants, it makes sense to involve those types.

Lion’s mane (Hericium erinaceus) growing between slabs of oak.
Oyster mushroom (Pleurotus ostreatus) mycelium in coffee grinds.

Fungal innoculation, composting, and utilizing animals like chickens to turn “waste” products and biomass into soil are in function making intentional use of an active decay cycle as mentioned above, which when we get down to it is the real mechanism by which nutrients are cycled through any living system. The ideal situation is one in which plants, fungi, bacteria, and animals all have a part in moving nutrients and enriching the soil, making nutrients and biomass available for other organisms in successions of consumption and decay.

The old school permaculture gurus like Mollison and Lawton were prone to saying “there is no upper limit to fertility”. While that’s probably just their typical overselling of the potential of robust farm ecosystems, it does get at the heart of the idea that thinking of fertility and agricultural output in reductionist “this in, that out” terms doesn’t take into account or understand the benefits gained by relationships between systems and organisms, that integrated systems work best when separate parts operate as a whole and feed back onto one another. By utilizing a robust and active decay cycle to facilitate the “velocity of nutrients”, we leverage the overlapping relationships and positive feedbacks within a farm ecosystem to create gains that exceed the sum of the individual parts therein.


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