Understanding water retention in soil

I've been reading a lot about permaculture over past few weeks and I have one question that I can't seem to understand and I'm hoping someone can explain it to me.

If I build up a good amount of organic matter in my soil in the forest garden the garden can then retain a lot more water like a sponge.

What I don't understand is that surely this would deprive the soil of oxygen (waterlogged soil) which is obviously not good for the plants.

If this is not the case can someone explain to me why this is?

I'm starting on an empty field soon which has had nothing but commercial grain for the past 5 - 10 years and there's nothing but clay soil. I want to understand what the organic matter does exactly and how I can increase it the fastest on this field.

Thanks for any help

I think that the thing you're missing is that this organically rich soil is more than just water retaining, the soil has a texture that creates space for air/oxygen while the individual 'clumps' of matter in this aggregate are still holding onto some moisture. People on here certainly have a better ability to explain this scientifically but if you dig into rich garden soil you will see that it is friable and relatively light but doesn't get dry and dusty. The presence of organic matter creates an environment to balance aeration and water retention. Basically, my understanding is that if you have clayey soil to begin with then the addition of biological activity will break up that dense structure to allow water to penetrate and slowly make the soil softer and easier for roots, water, and air to penetrate, while if you have sandy soil then the biological activity will create biofilm 'glues' that will develop more clumps to soak up and slow water draining through it. With the presence of moisture all sort of microbeasties get to moving making little tunnels of all sizes in the soil that are constantly shifting and making passage for air. Surely someone wiser than I can come along and give you a more precise explanation but that's, I think, a passable overview.

Thanks that helps quite a bit actually.

Another thing I need help understand is that nutrients in the soil will get used up over time from us removing fruit how do you keep the nutrient quantities up in the soil?

Do we constantly have to haul in mulch?

Even if we use animals they are eating nutrients that are already on the land.. they then produce the nutrient rich manure but it hasn't gain any extra nutrients than what were already there has it?

That is sort of the ultimate issue with any extractive system of production. In and ideal situation, all of the plants and animals in a given ecosystem would return all of their wastes (including their bodies) to the area where they extracted their sustenance while alive. In reality I think that we are always down stream from somewhere, and we are thus always receiving the 'escaped waste' of some other system. So yes, that might mean hauling in mulch or manure that came from some other system that isn't making use of it. There is also the fact that dirt is essentially a mineral aggregate with no biological activity to unlock these minerals, so by adding in biota you can make the minerals that comprise your dirt into the nutrients your plants and animals are getting from the soil. Depending on how much you remove from the system in the form of products (food, lumber, fiber etc) that will be either taken outside the system or tied up in a piece of clothing or furniture for decades, you will eventually have to replenish that. The rate of removal will dictate the rate at which it needs to be replaced. Again, I think.

What would be the best option for mulch?

It seems no matter what I can think of it's extremely expensive to get enough mulch hauled in for 100 acres

Bark chips online around 150-200 pounds per cubic meter
I'm trying to work out the best way to start on this field.

It might be worth me hauling in a large supply of mineral rich organic matter spreading it and then doing a crop of clovers and then comfrey before starting any sort of earth works or planting fruit trees.

Do you have any recommendations?

Many of the nutrients come from the atmosphere. It's helpful to remember that plants don't grow up from the soil, they grow down from the air. Mulch might help, but I would not recommend mulch on the scale of 100 acres. If you are looking to increase the organic matter in the fastest possible manner, I would personally recommend keyline plowing (to break the compaction from commercial grain operations), seeding it with a good pasture mix, and animals. A combo of cow/sheep and chicken tractors in an intensive grazing plan can do wonders for pasture in a small amount of time. The plants grow from the air, the animals turn those carbohydrates into organic matter, and that organic matter gets incorporated into the soil. The animals will help the pasture grow faster, and the pasture will feed the animals.  And of course, definitely start with a soil test… after years of commercial operations, you may be lacking in micronutrients or have a severe pH imbalance.

You might enjoy Richard Perkin's videos, he has talked about much of the details of his animal operations and how it has improved his soil https://www.youtube.com/channel/UC3111rvadtBPUY9JJBqdmzg

Can you help me understand where you say that most nutrients come from the air?

I thought the only nutrient that we could extract from the air was nitrogen?

I will do a soil test but I'm willing to bet that the micronutrients are practically 0.

So I need to figure out the best way to replace those too.

Most plants are made up primarily of carbon, and the fruits we extract from plants are primarily made up of carbohydrates (carbon + oxygen). That carbon comes from the carbon dioxide in the air that plants process. In a oversimplification: CO2 goes in, O2 and carbohydrates come out. There are of course differences between different plants and a lot of other chemistry-related details, but that simplification generally describes where the mass from plants come from.

Where do trees get their mass from? has a nice little article on the subject:

The mass of a tree is primarily carbon. The carbon comes from carbon dioxide used during photosynthesis. During photosynthesis, plants convert the sun’s energy into chemical energy which is captured within the bonds of carbon molecules built from atmospheric carbon dioxide and water. Yes, the carbon from carbon dioxide in the air we breathe out ends up in “food” molecules (called glucose) each of which contains 6 carbon atoms (and 12 hydrogen atoms and 6 oxygen atoms).

Ah right that opens my eyes a lot!

But don't plants breath out co2 at night? Is it simple a case of they breath out less co2 than they take in?

Also is there any mulch which is better for micronutrients or a way to increase micronutrients?

I'm not expert enough to answer your CO2 question other than to tell you plants definitely take in more CO2 than they exhale. In terms of mulch and micronutrients, yes — some is better for specific nutrients than others. I'd really suggest you start with a soil test. You definitely have more than 0 micronutrients! You'll just need to learn the state of your soil before you can think about amendments.

As Kyle pointed out, the big one is carbon. When someone talks about primary productivity of pastoral lands, they often express it in terms of dry matter. So if I've got a hectare of mixed pasture and I cut everything on it, dry it completely and weigh what is left, I might have 6000 kg of stuff. That is the dry matter component. Of this, about half (3000 kg) will be carbon by mass, and maybe 250 kg will be N. Both are nutrients, and both are required. It just happens that the ratio in my example (12:1 C:N) is similar to what you might aim for if you were building a compost pile, and it is why damp hay heats up to the point where it can combust.

Sorry for all the questions guys it just seems your all full of knowledge and I like to understand the bigger picture and inner workings of the soil.

What happens to the carbon in decomposing wood then?

If plants get carbon from the air what happens to the carbon in the soil/wood?

Maybe the fungi use some of it? I assume mushrooms contain carbon but I can't see how small organisms like fungi can use so much carbon?

No worries about asking more questions! Carbon from trees generally gets decomposed by fungi, but I found this diagram which may be more helpful. Even the smallest creatures can do big things if there are enough of them.

So most animals breath out co2 so they eat carbon foods. So pigs would help speed up woody plant matter decomposing as they can eat it.

Another question if you don't mind.

I want to setup a lot of "very large" ponds to farm fish.

I know for fish farming they mass produce hundreds of thousands of fish usually 1kg per 100l of water but I want to do it naturally so I'd need more water.

How can I calculate how many ponds I would be able to fill based on my rainfall?

I get an average of 20 inches a year here.

And ideally I'd like to have 10 separate ponds laid on to catch all available water with around 7.5million litres each.

I won't be able to aerate the water as I'd need a lot of electricity I assume to aerate that large volume of water so will have to rely on natural method.

But also if these ponds are sealed will trees and plants around the ponds still get enough water from rainfall?

I'm in the process of trying to design my idea and I think Im set on a design now I just want to make sure it would work

hau Steve, I have two threads on soil, what it is, why we need it and how to build it. they are in "Soil" One is quest for super soil  the other is What we need to know about soil

If you add 1% of soil carbon to your soil in the top 30cm, you increase the capacity of your soil to hold 14.4 liters of water per square meter.

If you raise SOM to 2%, it doubles that capacity of your soil to hold water --- 28.8 liters of available water for your plants per square meter.

It begins to slow down at 3 and 4%, but still, with the addition of SOM/soil carbon, the water-carrying capacity increases.

http://soilcarbonwater.blogspot.it/2006/03/soil-carbons-impact-on-water-retention.html?m=1

Table 1. Change in the capacity of soil to store water (litres/ha) with changes in levels of soil organic carbon (OC) to 30 cm soil depth. Bulk density 1.2 g/cm3

Change in Change in Extra water Extra water CO2 sequestered
OC level OC (kg/m2) (litres/m2) (litres/ha) (t/ha)

1% 3.6 kg 14.4 144,000 132 
2% 7.2 kg 28.8 288,000 264
3% 10.8 kg 43.2 432,000 396
4% 14.4 kg 57.6 576,000 528


As for soil structure, soil aggregates are a group of primary soil particles that cohere to each other more strongly than to other surrounding particles.  In healthy soil, the texture will be somewhat like cottage cheese, crumbling into little “curds”.  Root exudates and fungal glomalin serve as the glue that creates these little clumps of dirt that make the soil crumbly and aggregated.  Thus, if you desire healthy soil structure, you need to encourage the growth of plants and fungi both.  Healthy plants will pump root exudates into the soil profile, which in turn helps with aggregation.  Fungal networks will produce glomalin, which in turn also helps with aggregation.  Both plant roots and fungal networks increase the percentage of SOM without tilling or any mechanical soil disturbance.  

If that was TOO NERDY, all you need to know is this:

1.  Do not till your soil.  It will destroy the fungal networks and artificially pump too much oxygen into the soil, which in turn will cause a bacterial bloom that eats through your soil carbon.  

2.  Keep a living root in the ground throughout the year as much as possible.  As soon as you take one crop off, broadcast cover crop seeds and lightly rake them into the top inch of the soil.  

3.  Mulch as if all soil life depends up it.  It does.  Chop and drop your cover crops, or spread some other organic mulch like wood chips to feed the fungi and bacterial hoard.  Worms and other biota will integrate that mulch down into the soil profile where it will become stable SOM for decades to come.

I just re-read my post above and realize that I didn't directly answer you question.

Soil aggregation allows water to flow through the soil.  Soil Organic Matter (SOM) acts as a sponge, holding the water while still maintaining soil aggregation.  In other words, the soil holds more moisture but it isn't saturated to the point of totally pushing all the air out.

Humus is a spongy black "goo" that is SOM that has reached a point of decomposition where it is relatively stable—it no longer decomposes as long as it's isn't subject to direct irradiation by sunlight.  Humas holds 9 times its weight in water.  So when it rains and water flows into the soil profile, the soil aggregates (the cottage cheese curds) "grab" the water as the humus suck it up like a sponge.  

Further, the outer layer of plant roots is called the epidermis (same word human skin, true story), and have a highly absorbent film that swells when water touches it.  The cortex and epidermis act as a sponge to hold water until the plant can uptake it into the body of the plant and store it in the plant tissue.  While it varies from plant to plant, that absorbent outer layer of the root can swell to several times its dry size, making it a "bank" for holding moisture.

Fungi also swell when the mycelium come into contact with water.  Again --- another sponge in the soil.

It takes a heck of a lot of water to completely saturate healthy soil with lots of organic matter to the point where there is no longer any room for air.

How can I calculate how many ponds I would be able to fill based on my rainfall?

Steve,

This is a pretty open-ended question, especially in combination with the aeration. There are far too many variables involved to give a simple answer. It would take a book to give a complex answer. By this reductio ad absurdum, you could fill Lake Baikal with 20 inches a year, if you had centuries and low evaporative and exfiltrative losses. Adding a location or at least climate and soil data is imperative.

You will get the most out of the forum by asking specific questions after reading some posts on the topic you are researching. There are links to similar pages on the bottom if you are using a PC browser. This functionality is not clickbait, it is to try to give you the information without people writing essentially the same post again and again! I understand how you (or me when I started here) would be leery of following those, but is essential to glean from prior postings. This allows us to delve into more complicated questions rather than answer the simple ones on a continuing basis.

I am not trying to be a jerk, just hoping to show you how I got started here last year (and I am sure I asked silly questions and people helped me along). After a few months of researching you will be far ahead, there is alot of info on here. The advanced search function is also useful.