MamaStories

You guessed it: it’s time for another episode in the Calcium in the Soil and Plant series! Take heart: we’re getting close to the end (maybe only one more part to go?). Actually, it took me so long to post on this again because this one took me a long time to figure out. If you want to brush up on the previous parts, check out this page.

~

Part 8. Selective Nutrient (and Water) Uptake by Roots

Nutrients arrive at the root surface in three ways:

1. The first of these is root interception. As roots grow, they make direct contact with nutrients. This mechanism is less important because roots come into direct contact with only 1-3 percent of the soil volume exploited by the root mass. Mycorrhizae – fungi that form a symbiotic association with plant roots - can increase the surface area that roots can extract nutrients from. Calcium and magnesium, because they are so abundant, are often intercepted by root contact.
2. The second mechanism is mass flow, wherein plants, sucking up water (through the various pumps and pulls discussed in the previous part), also move the nutrients that are dissolved in it. Especially mobile (free) nutrients are “attracted” in this manner: nitrate-nitrogen, chloride and sulfur, which are never absorbed by the colloid and thus always exist in solution, and calcium and magnesium, which are held only loosely to the colloid. The drier the soil, the less mass flow.
3. The third mechanism is diffusion, by which ions in the soil spontaneously move from a point of higher concentration to a point of lower concentration (like in osmosis). Diffusion happens in the soil because the immediate root area, once it is depleted, has a lower concentration of the nutrient ions. Immobile nutrients like phosphorus and potassium, which have a low solubility, are strongly held by the colloid, and are only present in small concentrations, reach the root through this mechanism. The soil porosity is important here: smaller pores will block diffusion.

The last two mechanisms are the more significant mechanisms of nutrient uptake. Which one is predominant depends on the nutrients, the amount of water in the soil and the physical conditions (e.g., crumb structure) of the soil which dictates the movement of water through it.

Nutrients (especially immobile ones) then need to be wrested from the colloid by an ion exchange – the cation exchange capacity (CEC) talked about on a soil test. As we saw, the positively charged nutrient cations are held to the negatively charged colloid by a small electro-magnetic bond. When the root hairs release hydrogen ions (H+) and these come into contact with the colloid, they take their places on the colloid, breaking or weakening the colloidal-nutrient bond. The nutrients are knocked free and this makes them more available to be taken up by the root hairs.

Once the nutrient has arrived at the plant root surface and has been made available, the root needs to take it in: the nutrient-ion needs to travel from the root’s exterior to its interior.

As we saw in Part 7, the membranes of the cells making up the epidermis and the endodermis of roots are semi-permeable. This means several things. First, roots allow movement in, but not out, which allows osmosis to take place, by which water is taken up by the plant roots (cf. Part 7). Second, they allow only small solutes in, so they are impermeable to the large molecules of organic solutes (more about that in the next part). Third, some small solutes are allowed in, but others are not: plant roots are selective about their food.

It is the last aspect that interests us here. The uptake of the nutrients (as well as sugars and amino acids) by the roots is selective because of two main features:

1. First, the root membrane has channels that are ion-selective: one type of channel will let through only phosophorus ions, another fits only calcium ions, or potassium or nitrate, etc. Think of the toddler’s toy: the box with the star and pentagon and circular shaped holes into which only the star and pentagon and circular blocks fit. The root too is constructed like that.
2. The actual ferrying through these channels is done by ion-selective carriers: so-called coupling proteins that are embedded in the membrane of the root cells and that only react with specific ions, passing them on. Different plants require different amounts of nutrients, and so they will have different types and densities of ion carriers on the surface of their cells. These ion carriers are also most numerous on the surface of root hairs and root tips, which shows that roots are the main conduit for nutrient uptake in plants.

That explains the root’s selection of particular nutrients. Now, how does it select their quantity? How does it say, that’s enough?

As for water, its protein carrier is the aquaporin. Aquaporins are embedded in the cell membrane, forming transmembrane pores that conduct just water molecules. They prevent the passage of ions and other solutes by a filter (the ar/R filter) of amino acids that bind only water molecules and let them in (single file), while excluding all other molecules. When there is a lack or an excess of water, a gating mechanism changes the shape of the aquaporin so that it blocks the pore and stops the water flow. These gates can fail and an excessive amount of water can break the gates, as it were, and “drown” a plant.

Nutrients like calcium ions are taken up by different transmembrane protein carriers, which actively transport them, that is, they require energy to do so, because they have to pull in ions against their concentration gradient. For instance, there’s a good chance the root cells already have a higher concentration of calcium than the soil in the root area, but it might still need more. The energy required comes from a part of the cell (called the ATP, a nucleotide). If the plant has enough of a nutrient, it can simply stop drawing on the energy source. Also this mechanism can fail, and an excess of nutrients can lead to a toxic overdose and kill the plant.

So, however well-equipped roots are to select what the plant is in need of, it is still up to us, gardeners, to know how much of what a certain plant in our care needs and how much of it is present in our soil.

~

Next up, nutrients not in mineral but in organic form, and how those can make it into the plants. Yes, the egg shells. Finally!

O, that egg again!

We’ve arrived at Part 6 if this extraordinary saga of how calcium arrives and behaves in the soil (if I’ve occasionally typed “soul” instead of “soil”,  is it really a typo?). Click to catch up on part 1, part 2, part 3 and part 4 and part 5.

~

6. Soil base saturation and soil pH

The term “soil acidity” expresses the quantity (expressed in meq/100g) of the acidic cations (cf. part 3) that the soil can hold on to. The percent base saturation – another important term on your soil test results - is the percentage of the soil’s cation exchange capacity (CEC) occupied by the basic cations.

This is from our soil test:

This means that calcium occupies 50.6% of the total exchange sites. In other words, in 100g of my soil, 15.6 meq can hold on to cations, both basic and acidic. Of that, 7.9 meq is occupied, or saturated, by calcium, 1.65 meq by magnesium, 0.64 meq by potassium. So, as far as I can learn from the test results (*), 10.19 meq/100g of soil, or 65.3% of the CEC, is saturated by bases. That leaves 35.3% of the CEC (*) for the acidic cations (hydrogen and aluminum).

(*) Sodium (also a base cation) is not listed on my test results, which means its levels are low, so I don’t have a sodic soil (cf. part 5).

Not surprisingly, the greater the percent base saturation, the higher the soil pH. Because calcium is normally the major cation, by virtue of its abundance taking up about half the CEC (as in our soil), we can say that there is less calcium in acid soils and more in alkaline soils.

But if the soil is very alkaline (pH > 7.0), the high levels of calcium may have negative effects. For one, more calcium taking up the CEC very simply means that there is less room on the colloid for everything else. Secondly, an excess of calcium can no longer be adsorbed onto the colloid. This “free” or unadsorbed calcium begins to accumulate in the soil water and goes on to react with what other nutrients are present.

For instance, the free calcium will readily attract soluble boron (B-), which is an an-ion (a negatively charged ion), and form a nearly insoluble compound with it, thus making the boron less available to plants.

Excess calcium will also tie up, or immobilize into insoluble compounds, cations like iron (Fe++), phosphorus (P+++) aluminum (Al+++), zinc (Zn2+), copper (Cu2+), cobalt (Co2+), and manganese (Mn2+), as well as magnesium (Mg ++) and potassium (K+).

Lastly, calcium also increases the pore space in the soil by flocculation, which, as we saw in part 5, is desirable. But when pore space exceeds 50% of the total soil volume, the soil can dry out much easier, like sand.

In short, too much calcium in your soil and many nutrients become insoluble and thus unavailable to plant roots, and the soil structure is damaged to boot.

But, on the other hand, if the soil is very acidic, and thus if there is not enough calcium, many of the other cations can become excessive and thus toxic. Then calcium applications with limestone are called for. The aim when attempting to adjust soil acidity is never so much to neutralize the pH as to replace lost cation nutrients, particularly calcium.

~

Next time, I promise, we’ll finally meet the plants, and discover by what magical means they get the calcium out of the soul soil.

Brrrr, looks so cold with that new banner!

The hoop house beds get an airing

Inspired by Rob of One Straw, I went out into the cold, bright air yesterday  - gloves, woolen cap - to move the compost. The idea was to transfer it from Earth Machine no.1 behind our house, which receives our daily kitchen scraps, to the Earth Machine no.2 in the hoop house.

Right before our warm spell, when it was below freezing, I measured a balmy maximum of 64F in the hoop house. So, 64F inside while outside it was 30F! The observed inside minimum, however, was 20F - the outside minimum was 7.

The low nighttime minimum is explained by the lack of a heat sink. The only mass is the beds, covered with white row covers. Earth Machine no.2 is black, but it was empty, so not much there to retain the daytime heat.

Now no.2 is full, almost to the brim, with food scraps from the past weeks, fresh straw (as insulator, aerator and carbon) and actual compost - complete with worms!

What a surprise! I had expected some of the mass in no.1 to have barely started decomposing several months ago, and most of it not to have had a chance at all. And surely it had been too cold for worms. But no, the top half was teeming with the Red Wigglers that I had observed in my compost last Fall, before the cold set in. The quarter below that was almost finished compost. The bottom quarter had decomposed  somewhat, but it had ice crystals in it, so I left that in no.1.

All the rest I transferred to no.2 in the hoop house, where it will temper the indoor climate at night and where it might just get ready to go on the beds in early Spring.

These are veggies I hope to keep a little warmer:

An assortment of lettuces

Last year’s parsley, still very yummy

A whole bed full of greens and tiny broccoli, growing slowly but surely

This is the scene outside. We’re supposed to get new snow today.

~

(On a side note: Firefox seems to be having problems with the Flickr badges: it keeps on loading them. If this taxes your connection, press the X - stop loading this page - button. I hope they solve it soon…)

We’ve reached part 4 of this riveting story of how calcium and other nutrients make it into into the soil and thence into our vegetables and thence into our own bodies (and into chicken eggs). We’ve had some cliffhangers already, so be sure to check out parts one, two and three.

~

4. Solubility, carbonation and chemical weathering

It is the reaction of calcium and calcium compounds with water (see last part) that makes them soluble. Solubility or dissolution is the process by which a “solute” forms a homogeneous mixture with a “solvent” (here water).

This happens as the solute molecule breaks down and its ions dissociate. The positive ions attract the partially-negative oxygen in H2O and the negative ions attract the partially-positive hydrogen in H2O. The ions thus get spread out and become surrounded by the water molecules. The dissolution is complete, or in equilibrium, once it’s all been spread around. (source)

One calcium compound is more soluble than another. Calcium carbonate (our eggshell) has a very poor solubility (47 mg/L at normal atmospheric CO2 partial pressure and 25 degrees C). As we shall see, this is important for gardeners who plan to enrich their soil with eggshell calcium, but I will come to that later.

However, if carbon dioxide is also present, that carbon dioxide will react with the water to form carbonic acid (H2CO3), which is a weak acid – it’s the bubbly in our soft drinks. This carbonic acid will in turn react with the calcium carbonate to form calcium bicarbonate (or calcium hydrogen carbonate). So

CaCO3 + CO2 + H2O → Ca(HCO3)2

Calcium bicarbonate is five times more soluble in water than calcium carbonate—in fact, it exists only in solution.

This is the main process by which carbonate rocks of the Earth’s crust are weathered. As we saw, if water is saturated with carbon dioxide, it produces a mild carbonic acid. This is what happens with (unpolluted) rainwater (water plus atmospheric CO2), which has a pH of around 5.6 (polluted, “acid” rain has a pH of as low as 3.0), and with water in aquifers underground, where it can be exposed to CO2 levels much higher than the ones in the atmosphere.

In a process called carbonation, this water’s carbonic acid reacts with the solid calcium carbonate in rocks like limestone or chalk, forming calcium bicarbonate and dissolving it. This solution of water and mineralized calcium is then borne off into the soil, where it is deposited on the colloid, and where it waits to be again dissolved in water and made available to plant roots.

~

Well. That just brings us back to the beginning!

This is the third article in a series on how calcium and other nutrients end up inside our vegetables, and on how to interpret certain soil test results. It is preceded by part 1 and part 2.

~

3. Water and pH

Let’s investigate the water in the soil. For one, water brings the minerals to  the colloid, and it can take them away again (but so do the soil critters). Also, for reasons that will become clear later, calcium is available to plants only in dissolved form, that is, as part of a solution in water. Thirdly, this watery context heavily impacts the lives of soil critters. The most important factor in all these matters is the water’s pH or acidity or alkalinity.

As we saw, a molecule of water is composed of one oxygen atom and two hydrogen atoms: H2O. In a vat of pure water, most water molecules remain intact, but a very small amount of them react with each other in the following manner:

H2O + H2O ===> H3O+ + OH–

Water + Water ===> hydronium ion+ (an acidic cation) + hydroxyl ion– (a base)

The hydronium ion ( H3O+) is the chemical unit that accounts for the acidic properties of a solution, and the hydroxyl ion (OH–) is the chemical that accounts for the basic or alkaline properties of a solution. How?

Well, in pure water, the amounts of H3O+ and of OH– are equal, so the acid and the base cancel each other out, so pure water is said to be neutral, with a pH close to 7.0. Also, in pure water the concentration of H3O+ and OH– are in balance, so that an increase in the concentration of H3O+ causes a proportional decrease in the concentration of OH–.

This means that, if you add an acid like hydrochloric acid (HCl) to water, it reacts with some of the water molecules like this:

HCl + H2O ====> H3O+ + Cl–

And this increases the H3O+ or the acid concentration, throwing off the balance and lowering the solution’s pH to below 7, making it acidic. But if you add a strong base, such as calcium, to the water, it ionizes as follows:

Ca + H2O ====> Ca(OH-)2 + H2

Thus, the addition of calcium to water increases the OH- or alkali concentration of the resulting solutions, making the solution alkaline.
The cations (positively charged ions) we’re interested are either bases or acids:

• Basic cations: calcium (Ca++), potassium (K+), magnesium (Mg ++) sodium (Na +)
  Acidic cations: aluminum (Al+++) and hydrogen (H+)

The pH of the water that saturates the soil (see 4) regulates the solubility of minerals in that soil (see 4), thus their availability to plant roots (see 5), as well as the activity of soil bacteria (see 6).

~

Mm, on to that pesky problem of solubility, which took me a while to understand. For now let me add that I forgot all the chemistry I learned in secondary school (way back), and that this excursion has proved to be a fantastic rediscovery of all that magic.

So I did all that canning last year and ended up with a little more than what you see in the picture above. So far we’ve eaten half the tomato sauce, a lot of apple sauce and blueberry jam (but not half, not by a long shot), a quarter of the peaches, and some of the fig preserves. We liked all of those.

We did not like the green peppers (bitter, metallic taste, is that normal?) and the green beans, of which we have, sadly, a lot (good for a soup, or a casserole?). Those two veggies are going into the freezer next year!

Tomorrow I’m making split pea soup with two of the many pounds of dry split peas that I bought in bulk and store in the chest freezer. I’m also going to make an apple-peach crumble with store-bought apples and my canned peach pie filling.

My attempt, a while ago, of “root cellaring” store-bought (organic) potatoes on some stick on top of a bucket of water inside a large black plastic bin in the coldest part of our basement… resulted in all the potatoes sprouting in record time. Wha? They were in total darkness! Very strange. Could it have been the plastic? Maybe I should try a metal bin next time.

~

And here is the promised peek inside the hoop house. These pictures are from when it was still freezing.

All kinds of lettuces, mustards, and spinach, doing well

Russian kale, Swiss chard and broccoli (in back) lying down a bit but surviving. Can’t wait to harvest those carrots (to the right)

In the third bed the parsley is also laying low but surviving. The mache and claytonia that I sowed there way too late have germinated and the seedlings are tiny but fine, waiting it out.

I haven’t been in there since the thaw started (we’re in the 40s now during the day, and at the moment it’s raining all the snow away). I’ll have a look tomorrow, when (if it stops raining) I will move the compost from the Earth Machine that’s close to the kitchen (it’s too cold for the kitchen scraps to decompose, so that bin filled up really fast) to the empty one in the hoop house.It would be great to have some finished homegrown compost by the beginning of Spring.

We readied the basement area where I will start the seedlings again. I can’t wait to turn on those lights! We decided I’d stop mucking around with  various hot germination box designs, and buy a large seedling mat (with thermostat). If you have a particular one that you’ve have tried and like, let me know…. soon.

~

Don’t forget to scroll down for the second and, may I say, most riveting installment in the “Calcium in Soil and Compost” series, published a few hours ago.

It was the combination of finding an eggshell in the compost and staring at our soil test results that did it. I started researching and one thing led to another. But I figured it out, the basics of it, anyway. The result is a long text, so I’m serializing it over the next couple of days. I hope you find this sort of thing as fascinating as I do, and that it will help you with your own soil test results.

~

Digging and moving my compost heaps over a month ago, it was interesting to find eggshells and bones, all over a year old and barely decomposed. I keep sifting them out and putting them back into the heap. I figured it is the high amount of calcium in them that makes them so hardy.

This made me wonder how that calcium will ever make it into my garden vegetables. In what shape or form can the calcium in the eggshell, and the calcium originating from the bedrock, be taken up by plants?

It took me a long time to find out, but I realized early on that we first need to get clear on what this “calcium” is that we’re talking about.

Calcium in its elemental state is a metal - a soft gray alkaline earth metal (Wikipedia). But it is so reactive that it is never found in its elemental state, that is, all by itself. It readily combines with whatever it comes in contact with and becomes part of a compound.

Thus in the eggshell, calcium occurs as calcium carbonate (CACO3): an eggshell consists of 94 to 97% calcium carbonate. Calcium carbonate is also the active ingredient in agricultural lime, which is mined from limestone. Calcium can also occur in the soil as part of the compound calcium bicarbonate (Ca(HCO3)2), or as part of the compound calcium nitrate (Ca(NO3)2). And so on.

The “calcium” we will be talking about here is the calcium ion in each of these compounds, because it is only this ion that can be taken up by plant roots and thus form a nutrient.

If our interest is in calcium as a nutrient for plants, we need to consider:

1. its presence in the soil
2. its continued present in the soil
3. its interaction with water, and pH
4. its solubility
5. its relation to soil pH
6. its uptake by the plant
7. its availability when tied up in organic materials

1. Original presence of calcium in the soil: parent materials

First, of course, calcium needs to be present in the soil. So where would it come from in the first place? Calcium is abundant: the third most abundant metal in the earth’s crust, accounting for 3.64% of it. It is also, by the way, the fifth most abundant element by mass in the human body: what a beautiful correspondence!

Soil originates primarily from parent materials: rock. When rock is weathered or eroded, it is broken down. This can be a physical or mechanical process (abrasion by ice, for instance, or by biological agents such as lichens and mosses), or a chemical process (see 4). The left-over materials, when combined with organic materials, make soil, which is thus (almost) nothing but rock. I recommend the excellent soil page on Wikipedia.

Obviously, the more calcium (as well as N, P, S, K, Mg and all the micronutrients) is contained in the bedrock in your area (and the younger the soil), the more calcium will be present in the topsoil. So it pays to investigate what kind of rock your garden sits on: spend a day or two (or three) navigating the USGS map library, especially the surficial earth materials and bedrock lithological maps of your region.

(http://www.mass.gov/mgis/bedlith.gif)

~

Intrigued? This is only the first part of a series on calcium and other nutrients in soil and plants. Stay tuned!

Part 2 can now be read here.

Plangarden and Gimp are handy tools for moving things around in the garden without too much back ache. This is a preliminary map for the Spring 2010 Garden - not the veggies yet, but at least the structures.

1. The hoop house will be moved from its present position (light blue) over beds 8, 9 (still to be dug), 11 and 12 as soon as the cold weather veggies in those beds can do without it. If need be I’ll put cold frames over those beds.
2. The hoop house will move over beds 2, 3, 4 and 5, destined for hot house tomatoes, peppers and eggplants, so the soil there can start warming up early.
3. I framed in pale green those beds that still need to be dug.
4. I am still debating on whether to create raised beds or field rows in the south-western part of the garden (bright green). I will use the soil from last year’s potato towers there - these beds will hold lettuce and shade crops, so no fear of blight.
5. The old potato towers will become a large compost system.
6. I’m not sure if the north-west corner will become home to a small shed yet. It might be a good place for either the chicken coop (opening into the fenced off garden to the north, not to the veg garden, of course) or the beehive (would that be too close to human activity?).
7. The bright blue circles indicate rain barrels. The two barrels up front will overflow into pipes (blue lines) leading down to a  brook/wetland that will drain into a fish pond at the bottom of the front garden.

After two weeks of virtually no blogging, it’s lists like these that can get me going again. Yesterday I listed this week’s goals, today I’m looking at the Big Homesteading Plans for 2010. There is some sort of order here, but don’t ask me which.

1. Chicken coop (cob? attached to greenhouse? moat?) and 6 (?) chickens
2. Bee school and beehive
3. New patio and garden path, and small lawn in the back
4. Remove asbestos tiles in basement and create root cellar there
5. Plant bushes and small fruit and nut trees
6. Better fence around veg garden, and gates
7. Better, bigger compost system
8. Small garden/storage shed in veg garden
9. Start on permaculture flower garden up front
10. Front drainage and filtration “creek” ending in wetland/pond
11. Solar thermal collector/glass greenhouse (attached to front balcony)
12. Woodworking shop/pottery studio: this is a big one because it means demolishing our rotting shed, pouring concrete over a larger footprint, and putting up a frame. In our town we are not allowed to do those things ourselves. Also, it would cost a lot of money (this problem could possibly be solved by no. 17)
13. Earth oven for baking bread, pizza and drying firewood
14. Pottery wheel from the engine of our old dryer
15. Double our food self-sufficiency
16. Get serious about our emergency supplies
17. Finish novel, find agent, get published
18. Get serious about Transition in my town

To do this week:

1. plan Spring and Summer garden
2. inventorize left-over and saved seeds
3. read all the gorgeous seed catalogs that arrived while we were gone
4. order new seeds
5. figure out a better seedling “hotbox” - buy seed mats?
6. enroll in bee school, chicken class, and pottery

The plants under row cover in the hoop house have stopped growing, but they are all alive and well, just waiting it out. I am planning to get some fresh horse manure from my neighbor and creating a small “hotbed” in the hoop house for some early spinach. It would be interesting to compare the growth of those plants to the ones under the row cover, and to what extent the decomposing horse manure heats up the hoop house.

I am out there twice a day to clear the snow off and away from the hoop house so light can penetrate and the structure isn’t too stressed. I am happy to report that the hoop house has withstood heaps of snow and  gusts of wind, so our reinforcement of the top connectors seems to be working.

I managed to finish both volumes of Edible Forest Gardens when I was in Belgium and my first project will be to thoroughly re-assess our property. Digging holes and staking out areas will have to wait until the two-foot-thick blanket of snow has gone, but I will have to eyeball some of it and decide on some bushes and small trees.

It’s great to see the juncos play in the fluffy snow and vie for a place at the feeder with the cardinals and the passerines.