Soil + Water = ?

Hi, I need some help sorting out what happens with leaching of soil vs the beneficial trapping and slowing of water on your property. When does leaching happen vs nutrient accumulation? I live in southern Indiana and have property that has a lower field with some drainage issues to begin with so this topic is important to sort out. Here is the Wikipedia definition of leaching:

In agriculture, leaching refers to the loss of water-soluble plant nutrients from the soil, due to rain and irrigation. Soil structure, crop planting, type and application rates of fertilizers, and other factors are taken into account to avoid excessive nutrient loss.

There is probably a simple answer, but perhaps this topic can shed light on the difference between leaching and well managed water. Again, I'm not in a desert/arid climate. The last few years were very dry though, so hugels and swales have seemed like good ideas. Now I want to be careful not to swing too far in the water direction, if that's even possible.

Thanks!!!

Mud.


Leaching is always happening. It's why the Mississippi River has so much phosphate and nitrate in it that the mouth of the river is an anoxic dead zone -- so much bacteria and algae feeding off the nutrients that they don't leave any oxygen for the fish and other animals.

You can slow down leaching in two ways: (1) slow down the water flow; this is the idea behind wetlands, reed beds, percolation zones, etc. The nutrients still move, but not as fast, and maybe you have time to catch them with a growing plant in the middle of the flow. (2) have something in the flow that provides chemical binding sites that soak up the nutrients. Fresh activated charcoal is a good material to use for this, but it has a finite capacity, and when you reach x grams of nutrient per kilogram of charcoal, whatever that x happens to be, well, you are back to method #1.

Does this lower field have lots of productive vegetation that is thriving off nutrients washed down to it?

The minerals in the soil can either be leached down to the water table or mined and carried up by plants.
So your best bet is to lockup as much the water soluble minerals into trees and have the tree roots and "mushroom roots" mycelium bring up the escaping minerals back up to the surface.

In tropical rainforest where leaching is esp pronounce, most of the minerals are stored in plants/microbes.
And once the loop isnot closed (they are chopped down and removed) the land loses all fertility.

If I had to choose between leaching and not enough water, water wins everytime.
Hugels might be a good option for you, in the wet times it will keep the plant roots out of the water table and in the dry times, it will store water.

If/when you have sufficient precipitation that water sinks down through you soil until it reaches the water table, any water soluble nutrients that aren't bound up by the soil or plant roots will flow into the water table. The more clay or (preferably) organic material in your soil, the greater its capacity to bind nutrients and protect them from leaching. Leaching is particularly problematic for traditional industrial agriculture because it depends on application of chemical--water soluble--fertilizers and because it does not promote the accumulation of soil organic material. One technique that progressive industrial farmers use is cover crops to capture any plant nutrients left after harvest. The cover crop is incorporated back into the soil before the next harvested crop, increasing the organic matter and nutrient holding capacity of the soil and holding any trapped nutrients that the cover crop prevented from leaching.

Your drainage issues could be due to a heavy clay subsoil that is relatively impermeable to water flow. If so leaching may not be the primary problem. Presumably you have a layer of topsoil above any such clay layer and it may tend to be very saturated with moisture. Depending on the organic matter and clay content of your topsoil it will have a certain capacity to hold water and still have room for air. Plant roots require oxygen and soil that is saturated with water beyond its holding capacity will block root access to their source of oxygen--the atmosphere. Hugels in this low lying field will greatly increase those beds' capacity to hold moisture before becoming so saturated that air flow is impeded. Swales above the low field will slow the surface flow, storing the water in the soil above the low field.

Hey George,

These are good questions! Samantha Langlois made a great video course on understanding organic soil science. She covers leaching in there and much much more. Here's the link to the course:

http://organiclifeguru.com/course/organic-soil-building-for-the-organic-backyard-gardener/



Here's the intro video to the course:



Course link: http://organiclifeguru.com/course/organic-soil-building-for-the-organic-backyard-gardener/

John Elliott wrote:Mud.


Leaching is always happening. It's why the Mississippi River has so much phosphate and nitrate in it that the mouth of the river is an anoxic dead zone -- so much bacteria and algae feeding off the nutrients that they don't leave any oxygen for the fish and other animals.

You can slow down leaching in two ways: (1) slow down the water flow; this is the idea behind wetlands, reed beds, percolation zones, etc. The nutrients still move, but not as fast, and maybe you have time to catch them with a growing plant in the middle of the flow. (2) have something in the flow that provides chemical binding sites that soak up the nutrients. Fresh activated charcoal is a good material to use for this, but it has a finite capacity, and when you reach x grams of nutrient per kilogram of charcoal, whatever that x happens to be, well, you are back to method #1.

Does this lower field have lots of productive vegetation that is thriving off nutrients washed down to it?

The lower field has been cut for hay and left otherwise unattended for close to a decade. It does not grow much but a variety of grasses and "weeds". The neighbor who cut it last for their horses declined future cutting because of the supposed low quality and low yield of the feed.

The field emerges from mostly forested higher ground and also where our house is on the hill. There is plenty of contour left I'd say before the field finally flattens out. I could add some swales in places higher up as suggested.

S Bengi wrote:The minerals in the soil can either be leached down to the water table or mined and carried up by plants.
So your best bet is to lockup as much the water soluble minerals into trees and have the tree roots and "mushroom roots" mycelium bring up the escaping minerals back up to the surface.

In tropical rainforest where leaching is esp pronounce, most of the minerals are stored in plants/microbes.
And once the loop isnot closed (they are chopped down and removed) the land loses all fertility.

If I had to choose between leaching and not enough water, water wins everytime.
Hugels might be a good option for you, in the wet times it will keep the plant roots out of the water table and in the dry times, it will store water.

Thanks, it sounds like the swale / hugel combo can work well still. The tree recommendation you mention is also interesting because the forested area seems to really support a wide variety of fast sprouting trees like poplar and red oak which are very tall and thin. I have a beautiful mix of trees here, maybe 25 species in 7 acres of woods. As you get lower it becomes mostly pin oak, green ash, and black maple with lots of blackberry and spice bush.

With the perhaps 6" topsoil profile and lots of clay, I think everyone has helped me immensely in learning about the why of this property. From a productive tree standing I will be aiming for trees that tolerate heavy clay while also looking to deepen the topsoil. I have gone back and forth about using the field as a standard livestock area or just fill it up with hugels and forest gardens.

Walter McQuie wrote:If/when you have sufficient precipitation that water sinks down through you soil until it reaches the water table, any water soluble nutrients that aren't bound up by the soil or plant roots will flow into the water table. The more clay or (preferably) organic material in your soil, the greater its capacity to bind nutrients and protect them from leaching. Leaching is particularly problematic for traditional industrial agriculture because it depends on application of chemical--water soluble--fertilizers and because it does not promote the accumulation of soil organic material. One technique that progressive industrial farmers use is cover crops to capture any plant nutrients left after harvest. The cover crop is incorporated back into the soil before the next harvested crop, increasing the organic matter and nutrient holding capacity of the soil and holding any trapped nutrients that the cover crop prevented from leaching.

Your drainage issues could be due to a heavy clay subsoil that is relatively impermeable to water flow. If so leaching may not be the primary problem. Presumably you have a layer of topsoil above any such clay layer and it may tend to be very saturated with moisture. Depending on the organic matter and clay content of your topsoil it will have a certain capacity to hold water and still have room for air. Plant roots require oxygen and soil that is saturated with water beyond its holding capacity will block root access to their source of oxygen--the atmosphere. Hugels in this low lying field will greatly increase those beds' capacity to hold moisture before becoming so saturated that air flow is impeded. Swales above the low field will slow the surface flow, storing the water in the soil above the low field.

Without totally confirming by checking the field again, I think you've pegged my field. I wonder if doing a succession of cover crops plowed into the ground would add to the thickness do the top soil. Or how much it would and how long it takes to add an inch. Does anyone have experience taking this on with clay sub soil? I am looking at a cover crop mix in the spring plowed in or just cut and dropped.

I don't recall seeing the contribution of cover crops expressed in inches of topsoil. More often percentage of soil organic matter. A quick search of material I've downloaded from SARE (Sustainable Agricultural Research and Education, a division of USDA with lots of information online) turned up increasing SOM from 1.3% to 2.6% in five years. Alfalfa comes to mind as a deep rooted perennial that can penetrate hard soils. It and other legumes can add several tons per acre of nitrogen rich OM. You can download a book--Managing Cover Crops Profitably--free, that lists many cover crops and their suitability for multiple uses: http://www.sare.org/Learning-Center/Books/Managing-Cover-Crops-Profitably-3rd-Edition

George Meljon wrote: I wonder if doing a succession of cover crops plowed into the ground would add to the thickness do the top soil. Or how much it would and how long it takes to add an inch. Does anyone have experience taking this on with clay sub soil? I am looking at a cover crop mix in the spring plowed in or just cut and dropped.

It wouldn't hurt to turn under some different covers.

Another thing that might help, especially if you have some spots that stay flooded and too wet for most stuff to grow is to put in some bald cypress -- got to get a pitch in for my favorite tree. It does very well with thick clay subsoils, and once they get big and start putting out a lot of "knees", they slow down water flow and help to retain nutrients. I've collected a lot of bald cypress cones already this season and I'll be happy to send you some seeds if you send me a PM with your mailing address.

John Elliott wrote:

George Meljon wrote: I wonder if doing a succession of cover crops plowed into the ground would add to the thickness do the top soil. Or how much it would and how long it takes to add an inch. Does anyone have experience taking this on with clay sub soil? I am looking at a cover crop mix in the spring plowed in or just cut and dropped.

It wouldn't hurt to turn under some different covers.

Another thing that might help, especially if you have some spots that stay flooded and too wet for most stuff to grow is to put in some bald cypress -- got to get a pitch in for my favorite tree. It does very well with thick clay subsoils, and once they get big and start putting out a lot of "knees", they slow down water flow and help to retain nutrients. I've collected a lot of bald cypress cones already this season and I'll be happy to send you some seeds if you send me a PM with your mailing address.

A landscaper in this area touts the bald cypress as well and we even planted a bunch near the creek at my wife's family's place. Is the water slowing and nutrient retaining because of the size of the tree and it's knees or is it a function of the the tree's life activity? PM on the way...

Walter McQuie wrote:I don't recall seeing the contribution of cover crops expressed in inches of topsoil. More often percentage of soil organic matter. A quick search of material I've downloaded from SARE (Sustainable Agricultural Research and Education, a division of USDA with lots of information online) turned up increasing SOM from 1.3% to 2.6% in five years. Alfalfa comes to mind as a deep rooted perennial that can penetrate hard soils. It and other legumes can add several tons per acre of nitrogen rich OM. You can download a book--Managing Cover Crops Profitably--free, that lists many cover crops and their suitability for multiple uses: http://www.sare.org/Learning-Center/Books/Managing-Cover-Crops-Profitably-3rd-Edition

I appreciate this resource, it is looking good so far!

George Meljon wrote: Is the water slowing and nutrient retaining because of the size of the tree and it's knees or is it a function of the the tree's life activity? PM on the way...

Probably all of the above. They operate on such a different time scale than we humans, you would need a time-lapse camera with a 50 or 100 year loop to see what the tree is doing and how it reacts to its environment. Why they form knees and what purpose they serve is really not well known.

Another thing that might help, especially if you have some spots that stay flooded and too wet for most stuff to grow is to put in some bald cypress -- got to get a pitch in for my favorite tree. It does very well with thick clay subsoils, and once they get big and start putting out a lot of "knees", they slow down water flow and help to retain nutrients.

No doubt bald cypress will thrive in soil too saturated for most other plants, even standing water. And that's fine if you are mostly concerned with is having something growing. I'm not so sure it will help if your goal is to reduce the saturation of the soil to the point that you have more options of plants that will grow and produce food or fodder. As I recall the original post was a question about leaching, so it's not clear to me what George's goals for his wet field are. Maybe cypress will help him; maybe not.

There are a few remaining cypress swamps up and down the east coast of the US. I lived near the northernmost of these--on the Delmarva peninsula. In general the area has very sandy and porous soil. The swamps form where there is an impermeable clay pan that keeps runoff and contributions to the water table to a minimum. The cypress excel at growing in standing water; various other tree species grow in adjoining areas where there is some soil, though for much of the year it remains saturated or near saturated. The cypress do slow down the water flowing through the system and contribute organic material that feeds those areas of wet soil, but I don't think their roots penetrate the soil pan and help break it down so the area becomes less swampy. The areas that were historically cypress swamp on the peninsula have been greatly reduced by ditches cut down through the clay pan to drain areas for agricultural purposes. The swamps remain where this action by humans has been restricted or not practiced--so I'm thinking the cypress don't really promote drainage of saturated soils. But then the remaining swamps are intriguing to explore by kayak and are a valuable part of the ecosystem. One of the fascinating things you'd come across in the swamps were trees blown over in storms--there are severe nor'easters and hurricanes occasionally. The root structure would be 15 to 20 feet in diameter and a couple of feet deep. The cypress also provide shade that would tend to reduce evaporation, so I'd bet that they played a role in preserving the niche to which they are somewhat uniquely adapted.