I love your question. I have wondered the same sort of thing; if humankind vanished today, would the work I did make a fertile patch that lasted, and would the bare, untended soil take a long time for nature to reclaim.

I think human's general effect on soil tends to be negative. I think we have been 'mining' the soil of its fertility.

I used to live in Champaign, Illinois. The topsoil in central Illinois was once 10 feet deep. It was boggy with slow drainage and grasses thrived in the area before the first settlers came and started draining the soil of its water.

Since that time, farmers have been growing corn and soybeans and the soil has steadily wasted away.

Here in Idaho, there's something of the opposite thing going on. The farmers here rely upon flood irrigation, so they have leveled the soil from its originally uneven state, to a slightly sloping but flat state. Then the land gets flooded to water the plants. The shallow aquifer used to get so full that people's basements would sometimes flood. Locust trees thrived on the ditchbanks and fence lines.

Farming in Southwest Idaho area was beneficial to the tilth of the soil.

Penning horses onto a small area is going to be hard on the soil. I think that compaction is the biggest problem. But it seems like the fallow horse yards in my neighborhood bloom with grasses and weeds when they sit empty.

I think that improving the fertility of a patch of ground has a lasting effect. The soil where my compost bins sit has changed. I have to be careful not to remove too much of the compost out of my bins or I remove what was soil and create a depression. I should probably move my compost bins to a spot closer to the gardens so that the soil under the bins can be used as garden beds when I move the bins again.

One of Eliot Coleman's book on gardening talks about a system of movable chicken coops and free range chickens, a system that improves the soil.

So, I believe that the improvements to the soil will last, especially if it involves lots of organic material.

For eons the midwest prairies were a self sustaining environment, until we humans came along and changed the conditions, so in most places Ma Nature has built into the ecosystem self sustainability and if we left that would, eventually, return.
What we do to make soil good and healthy needs to be done on a regular basis, just as Ma Nature did and does, but mostly we intervene and change all the conditions. we throw away renewable resources and purchase non renewable resources to replace those renewable resources we threw away. You could create an environment that is self sustaining, provided you never removed from that environment anything, or you found a means of replacing what you did remove.

Yes, the above two posters touched on the key to lasting 'improvement' - self sustaining conditions, which means not harvesting the biomass but letting it return to the soil that created it, so new biomass can be creating in turn.

Some soils are naturally lean. Who are we to say that our 'improvements' are really better?

And just what are those weeds blooming in abandoned horse pastures? not what was growing there before clearing and grazing, I'm sure. There are many weeds that thrive in pastures because they outcompete other plants given conditions of compaction, hoof traffic and overgrazing. It's not natural for one area to receive constant horse traffic and horse grazing for extended periods. Horses, and all grazing mammals, by nature migrate among pastures constantly.

Soil 'improvement' will only last as long as the conditions that created it. Here, the natural conditions over large areas are coniferous forest on lean, gravelly, glaciated soils with abundant rainfall. The soil is lean by nature, yet still produces some of the finest timber, and in some of the largest quantities, of the whole world. It won't do that indefinitely of course because we keep harvesting and removing the timber, instead of allowing it to fall to the ground and return its biomass to the ecosystem. In nature, fallen trees feed the soil, and tree and shrub seeds sprout preferentially in fallen decaying logs. Not to mention the abundant lichens, mosses, mushrooms, berry producing plants, and all the other stuff besides trees!

What is soil fertility? it's organic matter, which in order to increase soil fertility, has to be eaten. When it's eaten, it's gone, and more has to be added, one way or another. You have to eat every day to stay alive, right? Soil is alive too, with microbes and fungi and worms and all kinds of stuff. That's what soil fertility is, and it all has to eat regularly too. Plants and animals remove organic matter and mineral nutrients and water from the soil, and what they remove has to be returned on a regular basis to keep the cycle going.

If your property were abandoned and left to its own devices, the vegetation that grows up will return its biomass to the soil, so long as no one interferes by raking or weeding or pruning. As biomass accumulates, conditions will change, and new species will be able to grow there, while others may be forced out. It's a disturbed environment, after all, and it will take time for the natural community to reach some kind of equilibrium.

The posts have been thoughtful and largely correct. The University of Minnesota has done very interesting long term studies of soil fertility and the effects of farming it over the years on the humus content of the soil. Virgin soil farmed steadily for 25 years causes such a loss of biological activity the soil will no longer support a crop without a massive addition of synthetic fertilizer which causes more loss of microbial activity. Soil fertility is measured by trapping carbon dioxide at the soil surface its abundance indicating biological activity. Al

Gaitten asked:

How long does soil improvement last?

A very good question. It's one I've often thought about myself, when hauling home compostables or adding organic materials to my garden.

The clearest, simplest answer I can offer from my reading and gardening experience is "It depends."

'Soil improvement' can include organic or mined or manufactured or processed inputs (usually called 'fertilizers') and various kinds of organic materials in various states (usually called 'soil amendments' -- although many of them, like compost and manures, are also direct or indirect aids to increased fertility.)

Some of those inputs don't last very long. Nitrogen, for one example, can leach out with water flow, or outgas up in the air. Plants will use most of what nitrogen remains in the soil within a year, except what is temporarily tied up by bacteria, fungi, and the rest of the microherd.

However, from the context of your post, it seems you are wondering how long organic materials will remain in the soil. Again, the answer is "It depends."

There are multiple factors which influence how long OM remains in the soil. I would guess the four most important external factors are temperature, soil moisture, air supply, and cultivation.

When soil is warmer, it becomes more biologically active. The soil microherd consumes the organic materials; this process improves soil fertility and structure (tilth) but over time it also degrades and consumes the organic materials which are the microherd's food source.

When soil is damp (but not soaking wet like a bog) this also stimulates the microherd and consumes the OM.

When there is good airflow in the soil, allowing oxygen to reach the microherd and carbon dioxide and other gases to escape -- aerobic conditions, in other words -- the microherd will grow and continue to reduce the OM.

Cultivation -- digging or plowing or harrowing or raking the soil -- also increases airflow, especially in heavier soils with high amounts of clay and silt. One of the major advantages of no-till and reduced-till cultivation is these approaches help to increase soil organic matter over time.

Temperature, moisture, air, and cultivation are largely physical processes. They each have biological and environmental impacts, certainly. Yet soil is more than just a physics project -- soil is a chemical and biological environment, an ecosystem.

You also asked:

If my property were abandoned today and completely neglected, would the vegetation that followed drain the soil of all the benefits of my soil improvements over time? Or will improved areas likely remain improved for decades to come.

The answer to this question depends first on what kinds of organic materials are already in your improved soil, and what organic materials would be returned to it by being neglected for years.

If the gardeners who built up the black delicious loam you describe used organic materials which are very slow to completely decompose -- the cellulose and lignins in wood are two examples -- the soil as-it-is-now will likely remain in good quality for a decade or more.

During that time, assuming the garden soil didn't become heavily compacted with foot or vehicle traffic; assuming there was good rainfall for growth, but not too much; assuming good sunlight in the growing seasons, and amenable temperatures for growth -- existing weed seeds in your garden, and weeds brought in by wind and birds and animals, would likely create a new kind of ecosystem. Call it a weed garden. :)

Within one or two decades the plants growing there would likely become bigger and taller bushes and shrubs and trees, their roots reaching further down and wider. These bigger plants would leave more debris on the surface which would decompose and recycle the organic materials originally taken from the garden. Their decaying roots and root hairs would also tend to maintain (and gradually increase) the amount of soil organic matter over time.

Wind and water erosion, earthquakes, and other natural forces could slow or deter this process. However, under most natural conditions for most of the time, soil gradually continues to improve, until the content of organic matter held in the soil reaches an optimum for the climate zone where the soil is located.

Cooler and semi-arid climates (like the Canadian Prairies, the great plains of the US, the Ukrainian and Russian steppes) tend to leach fewer nutrients and encourage grassland growth. Which tends to build deeper layers of topsoil and create more below-ground organic reserves.

Damper and warmer climates (like the eastern seaboard of the US, the rain forest of Pacific northwest in Canada and the States, and the tropical rainforest in South America) tend to concentrate their biomass above ground, in trees and in the plant and animal life living on the trees. These soils don't hold as high a concentration of organic materials.

All of the above doesn't really speak directly to your ultimate questions, Gaitten -- sorry :) -- but from my understanding, the many processes going on in soil creation and degradation all interact with each other in so many different ways, it's difficult to give a clear simple answer to what you asked.

In three years of gardening here in my downtown Toronto back yard, I've built compost piles beyond counting from kitchen scraps, yard waste bags hauled home from nearby streets, and the used coffee grounds from a local coffeeshop. I've dug in leaf mold and built lasagna piles, even tried an Interbay mulch pile which produced 6-8" of beautiful compost in one season over a 5' x 8' garden bed.

In my experience, and from my reading, adding large amounts of organic materials -- 2" or more of mature compost topped with a good mulch to protect it from wind and rain erosion -- has an immediate beneficial impact on the garden soil in the following growth season. Plants are bigger and healthier, more resistant to pests and diseases; they produce more.

Yet without fail I've noticed the positive affect of the mature compost and mulch degrades within a year -- whether left on the surface or tilled in, shallow or deep. Unless more organic material is added, plants don't grow as well in following seasons.

As a relatively new composter I found this discouraging. When I researched online I discovered what I half-seriously call The Dark Dirty Secret of compost: it goes away.

Roughly 85-95% of raw fresh organic materials disappear in the first year compost is made and applied to soil. Of the remaining 5-15% about 1/3 disappears in two to five years, consumed by the microherd. 1/3 may last 5-25 years. 1/3 might -- might -- still be around one hundred to a thousand years from now.

It's my personal conviction, based on reading and on my own experience, that intense soul cultivation, excessive watering, and the heavyhanded use of fertilizers (especially nitrogen and potassium) increases the breakdown of longterm organic materials in soil. Mulching and reduced tillage seem to slow this breakdown and build better soils faster, in my garden.

This past year I've started to experiment with green manures and I'm hopeful they will also help improve the soil. It's a pleasant thought to imagine some small part of the organic materials I add to my garden may still be helpful 10, 25 or 100 years from now. Assuming no-one turns it into a parking lot or a construction site. :)

You might find by Steve Solomon's book Organic Gardener's Composting a useful resource, especially Chapter Eight, "Maintaining Soil Humus." The full text is available free online at his excellent site, soilandhealth.org. Solomon explores these kinds of questions in far more detail and with references to other soil and gardening texts.

All the best,
-Patrick

Sometimes it can be subtle things that effect soil fertility. I think that the soil fertility 'pump' can be 'primed' and a virtuous cycle then causes fertility to spread. An example would be the gradual encroachment of plants onto lava in Hawaii. Something like bird poop can create a toehold for a plant, and it will cause soil to collect.

In Yellowstone, the reintroduction of wolves has indirectly caused streambanks to grow more trees. Park Naturalists have observed the change. They discover that wolves keep elk on the move so elk don't browse the tips of young trees in one area so badly. Beavers will come and make dams with the trees, that floods the land, more trees, soil gets deposited in the slack water behind the dam. You get the picture, but who would have made the connection between wolves and trees?

Mankind has been pretty rough on natural systems. During the settling of North America by European immigrants, many beaver were trapped, many trees were cut down, much soil got washed down rivers. The soil in New England rapidly became depleted and people moved west to find soil that would support them the way it used to support them in New England.

Many Native Americans lived in New England. It must have been a paradise of ample deer, fish, chestnut trees, etc. Someday it will return to that, but not soon.

So, I think the trees that I plant, and the compost that I make and till into the soil, will help restore my home town to its natural glory.

idaho_gardener wrote:

So, I think the trees that I plant, and the compost that I make and till into the soil, will help restore my home town to its natural glory.

Amen, my friend. Amen.

No matter how those of us who write here may differ on the best or the simplest ways to make the world better -- I don't think anyone who reads here or seriously posts in this place lacks the desire to make a better world. Even if the earth we want to make better is only a few feet of barren ground we ponder and frown at and worry over.

William Blake wrote these beautiful lines many years ago, and it surprises me more gardeners don't inscribe them over their desks. Especially composters.

To see a world in a grain of sand,
And a heaven in a wild flower,
Hold infinity in the palm of your hand,
And eternity in an hour.

This may, perhaps, be a simpler answer to Gaitten's ultimate questions.

On a night when much of the world anticipates the celebration of the birth of a child, perhaps we can contemplate -- and realize, if only in our minds -- how powerful and important what appears small can become, over time.

Here's wishing a merry Christmas to all who keep it -- and equally so, the very best of this season to all who celebrate in other ways.

All the best,
-Patrick

All wonderful answers above.

One thing you have to keep in mind is that the soil is literally a living thing. It needs fairly constant feeding, like every other living thing. I know many people apply compost, grow a green manure, layer on mulch, and then wonder why it disappears. They forget that when the mulch in ON the soil, it isn't IN the soil. Once it's IN the soil, it needs to be replaced. Soil improvment is an ongoing operation. Forever.

Look at Nature: There's a lot of fast growth when the soil warms up in spring, the grasses being among the first. As summer progresses, the deeper-rooted perennials catch up and take over, while the grasses (which have more shallow roots) start to wither and lie down, forming a natural mulch on the soil. But it doesn't just lie there, the part that is touching the ground is being attacked by the microherd and the fungi. Then the earthworms come up at night and eat the parts that are broken down enough for them to handle. The earthworms poop out their castings underground, and their tunnels allow any rainfall to soak into the soil. As the last of the grass is being incorporated into the soil, the leaves start to fall, which adds another protective layer to the soil, which will again be worked on by the soil insects and microbes. Winter tends to freeze the soil to some degree in most places, and the heaving of the soil, the snow and the rain all add their benefits.

Livestock pastures are usually poorly managed. There is more to good soil than manure, which, with urine, is more like toxic waste. Then the soil is compressed by hooves.

The animals in a confined pasture eat all the best herbage first, then the less attractive plants, and worst stuff they won't touch, like the ox-eye daisy here in western WA. The best and the medium-grade forage is never given a chance to multiply, but the wild daisy and the tansy and the other undesirables have no competition, are hardy to lack of rain, and do their very best to produce all the seed they can. So what is the pasture seeded with, year after year? All the noxious stuff that the livestock won't eat.

But suppose you handled your pastures differently? Suppose you didn't let your horses take down all the good grasses to the soil, but moved the horses into another pasture after a relatively short time? Then suppose you seeded the empty pasture with a mix of desirable grasses, and maybe even watered it in dry periods? That soil is going to produce many more pasture days than the old way.

But what if you took the horses off it altogether and sowed it with a mixture of grasses and clovers? Then, instead of taking the "crop" off the land, suppose you just mowed it high and let the herbage lay on the ground and return to the soil? What would happen is that these plants would add a lot of biomass to the soil. The microherd would multiply, the deeper-rooted plants would bring up more minerals and trace elements, the shallow-rooted plants would constantly grow and die off, creating more channels to absorb rainwater and oxygen. All this would start to buffer the effects of the years of horse damage.

Your beds with the wonderful soil HAVE been cultivated, but it was done Mother Nature's way, using plant roots, moles, gophers, voles, and earthworms. She kept it covered with a collection of various natural mulches, which often died, laid down on the surface, and were incorporated into the soil.

Ma Nature knows what she's doing -- she's got it perfected.
"If my property were abandoned today and completely neglected, would the vegetation that followed drain the soil of all the benefits of my soil improvements over time? Or will improved areas likely remain improved for decades to come."

If you did the job right, Mother Nature would just continue improving the soil. If you messed up in one way or another, she would fix it as best she could, ultimately bringing it back up to par.

First, she brings in the power blower (wind) and hoses around a lot of grass and weed seeds. If there are bare spots, she will fill them. Soon, everything is growing, and the soil is covered, even if damaged, because only what CAN grow there WILL grow there. Other seeds, finding the wrong conditions, will often just sit there and wait until a more optimum time for them, sometimes for many years.

Oftentimes, the seeds she plants are very deep-rooted, like dandelions, and they bring up nutrients that were washed out of reach of more shallow-rooted plants. The dandelion leaves die and lie on the soil, then are incorporated into the top few inches of the soil. This can change conditions for some of the seeds which have been lying dormant. These can be more weeds, or shrubs which send down even deeper roots than the dandelions, and bring up more and different nutrients. A few birds land in these shrubs and poop out some of the seeds they've been eating. Some might be tree seeds, scarified in the birds' crops, soaked in their digestive system, and pooped out with some additional moisture and a blob of fertilizer. Some of these tree seeds sprout, a few survive, and one or two have some tiny edge over the others, shade out the weaker ones and take over. They grow, shedding their leaves in the fall and mulching the earth. The earthworms, insects and underground rodents have continued doing their jobs, aerating the soil without exposing much of it to the drying sun, and creating tunnels to trap and absorb rain.

Every year, the soil becomes more friable, more healthy. If it was highly acidic or alkaline, that has probably moved at least a bit closer to neutral.

As far as I've ever heard, Man is the only creature that destroys the soil. And Mother Nature keeps fighting to fix it.

Who are we? We're a silly bunch of creatures who don't even know what questions to ask, much less to know and actively provide the answers.

Sue

The answer to that is as simple, and as complex, as soil it's self. The simple practice answer from my personal experience: I add something like one foot of material the first and second year, and about 6 inches ever year after that. The extra seems to be needed the first couple of years for better weed control, extra needed soil nutrients, and because the soil needs more help in the beginning.
The complex answer is to look at the composition of what you harvest and what does that take from the soil? That needs to be replaced. Now some of that will be replaced as the particles of the native mineral soil weather and break down. A good example of this is calcium if calcium is in the native parent mineral soil to start with. For us in the West who irrigate, most get added calcium and sodium from the water too. If you have lightning, you also get nitrogen from your rainfall. If you grow legumes, you may be getting nitrogen from the root activity of the plants as they grow. So some nutrients come from other sources, depending on your soil and your location. then what is in your organic material can vary too. And some soils are so needy in some elements, that you need to add mineral components also, although that is not as common as you may think. PH of soil also effects what and how much of various elements are available. Also, as your soil matures it will build up reserves of usable, available, nutrients. So, from a scientific and measured point of view, it can be a little bit complicated.
Again on the easy side, once you have used a surface mulch (or "lasagna") for 2 years, dig a hold 2 feet deep and then look at the side of the hole. You will see very distinctive layers that are the "profile" of a healthy soil. As the soil "matures" and these layers develop, your soil will work better and do the job it was intended to do.

We have built our new home on 5 acres that had once been used as an oat field. It has been left alone for the last 18-20 years with just an occasional mowing to keep the fire danger down. Now that we are starting to make flower and vegetable gardens we wonder what happed to all the organic material from the oats that were left to decompose over all those years. Our soil is sandy, rocky loam. We never find any worms in it except in the vegetable garden I started here 3 years ago and worked in lots of compost. Now, I have been piling on the horse manure from my neighbors horses. I wonder, why isn't the land, left fallow for so many years in better condition?

Hi caavonldy

As far as the organic material from the oats goes, there are several variables that may have taken place. Was the straw from the crop; baled and removed, chopped and incorporated or burnt in the field? Each of these may be common depending on the farmers situation. Another question that comes to mind is the rotation of the crops. Was this field used in a standard rotation or was it consistently used for oats? Had animal manures ever been applied to the field or were only synthetic fertilizers used? What grew on it for the past 18-20 years and how vigorous did it grow? Any herbicides used on the land at all?

The link attached has a small chart about half way down on the right hand side. It attempts to depict the organic material depletion in cultivated soil. It is interesting to note that the organic material can be restored with proper management, but it might take a while.

We are seeing soil depletion effects more and more on the Canadian prairies. There is increased attention being paid to our farm practices and hopefully we can work to fix this but I suspect it will take a while.

Lloyd

Here is a link that might be useful: Organic matter depletion

The land was used for oats 20 years ago. Since then nothing has been done at all except for mowing if it got too tall. When it was mowed, the oats/straw were left on the ground. No fertilizers were ever applied until the last two years when I started to set up beds for flowers and veggies. The oats keep reseeding themselves and growing in the winter when it rained. since we moved here, we mowed and plowed/leveled the land before building on the lot. Every winter the area where we have not planted on still sprouts oats. My DH keeps it mowed and as long as it rains, it looks like we planted it in lawn. Too bad it drys up in the spring. With 5 acres, its just too much to irrigate year round.