Robin's eggs
Robin’s eggs

Some time ago (April 16) we returned to the field of the Full Moon/Grief walk. Our group was smaller this time. We had timed our congregation to dusk, because that is when the male woodcock performs its sky dance for the benefit of the females of the species. Woodcocks are crepuscular, most active around dusk and dawn. Every year around April,  a flock takes up residence in this particular hay field in the Greenways Conservation Area in Wayland, to woo, mate and nest. Every evening for a month or so, one, two or three males perform a dance in the sky above the wide-open field for who knows how many females watching from the bushes on the field’s edge.

It’s too dark to spot him (let alone the silent females), so you mostly catch the woodcock by ear. When on the ground, he makes a distinctive peent-ing sound. I think it means: Are you watching me? Here I go! Then you know he’s taken flight when you hear the whistling, twittering sound from his voice and the airflow through his feathers. If you’re lucky to spot him against twilit (or street lit) clouds, you’re taken aback by how diminutive he is, and his lack of grace. He is all wings, a small ball of feathers flung up into the sky in a messy, wind-driven spiral. What falling up would look like.  Your eye invariably loses him against the dark horizon, the dark earth. Still, you know he landed, and more or less where, when he betrays himself with his peent.

But as I describe it – and even as Aldo Leopold describes it, much better than I can, in The Sand County Almanac – it just sounds way too… big. I’m afraid that I’ve raised your expectations, that when you go looking for the woodcock you’ll be disappointed. He is really only the size of a robin, a small, ruffled silhouette barely distinguishable  against the pewter grey sky. The peent is subtle at a hundreds yards’ distance. The pretty twitter is even more subdued and you have to turn your head to aim an ear at it. The wind will try to rob you of your already fragile experience of him.

But we were there to witness the woodcock and we were determined. There we stood, seven humans, in the middle of the grey, breezy field, hummocks of hay, timothy and weeds still small, but tenacious, underfoot.  ”Where is he?” someone whispered. “Wait. Listen.” Peent! Snickering. “That sounds kind of rude!” Then, ”He’s up! Hear it? Sounds like…” and “I see it! It’s there!” I looked from the sky down to the group: six dark statues, all with heads raised, some pointing. The question presented itself: what are we doing? What’s with the words, the pointing  (like that helps anyone)?  The answer struck me hard: you have to care.

There were some among us who didn’t care. Their words, their body language were of puzzlement bordering on disappointment. Was that it? Was it these woodcocks? (There were three hard at work in the field that day.) Or are all specimens of their species this… fragile? Or was it the place, the car noise and orange street light? Or the weather, the thieving wind? No, it was that they couldn’t bring themselves to care.

I realized that I was having to work hard at it myself. These birds, their dance, they live on the edge of our common senses.  I was pushing my caring to act like an extra sense to allow me to experience these birds. I wasn’t just paying attention, though that too was necessary. Not content with just hearing two faint sounds and seeing a ghost of a shape, I was also investing myself, digging deep, giving much, caring, so as to drag every bit of marvel and awe out of the experience.

What I found was, again, grief, quite specific this time. This field, where the woodcock has been coming, decade after decade, gets mowed around the time the females lay their eggs on the ground on the edge. The noisy, colorful combine will come for these dull-colored, quiet birds. This field is also being considered for sports field. The flash and shout and strife of bats and balls and orange-clad running bodies, the flood lights at dusk, the fuming parking lots, the weekly mowing, the trash… the woodcocks will not compete.

There are two extinctions here. The birds’. Ours, at least the extinction of a part of us.  The suburban noise of the leaf blower, the honking cars, blaring sirens, the slick feel of our plastics and shock of ”butt-kicker” movies, the flash of street and traffic lights, computer screens, the clothes we wear have robbed us of our experience of these dull, small animals, who are nevertheless  more alive than cars, leaf blowers, movie action, computer models, gaudy fabrics, plastics…

But they will not show themselves. It is up to us to care about them. So unless we can get more people, more than just seven, to come and stand in that field and to care that much, the Greenways’ woodcock’s passing will not even be noticed, and we will have lost yet another opportunity to connect, the practice connection, to care.

Been thinking about that slope: will the soil support what we ultimately want to plant there, and how do we best prepare it?

This south-west facing slope, relatively sunny – somewhat shaded from the southeast and northwest, more so as you go further down the slope – will be a fruit orchard: we’ll plant blackberries and blueberries on top, and currants, gooseberries and elderberries further down. We’d also like to stick some semi-dwarf fruit trees in there if we can (cf. Garden Plans for 2013 and Beyond). We’ll coordinate all these in guilds, of course, at least at first so the guild can nurse them to maturity.

Michael Phillips’ basic recommendations for the rhizosphere (root-sphere) of an orchard are:

  1. pH in 6.3-6.7 range
  2. Calcium (Ca) between 2000-3000 lbs/acre, phopshate (P2O5) and potash (KO2) both at least 200 lbs/acre
  3. carbon-rich, fungal, porous
  4. organic matter (OM) a minimum of 3%, better 5% and above

In 2009 we had a soil test done of the soil in the vegetable patch before any plants went in. The situation in the veg garden has changed quite a bit, I should hope, and a new test is planned. We never really tested the soil on the slope, which is mainly subsoil dumped during the work on the septic system before we bought the house.  When we terraced it we added brought-in loam and spread quite a bit of compost (for the strawberries), but it wasn’t as intensively taken care of as the veg garden soil. The soil in the broad path didn’t even get that. There especially the erosion continued. So, another soil test is in order before we begin on that slope. But while waiting for the soil to defrost and dry out, I’d like to play around with the old test results and practice my “soil detective” skills.

In the following I rely heavily on Phillips’ incomparable study in Holistic Orchard (p.61-74). I also refer the undaunted reader to my Calcium in the Soil Series, a very long but (I think) valuable explanation of soil test results and some of the soil chemistry that is relevant here.  That series starts here.

  • pH and CEC

The pH at 6.4 – 6.5 looks good. But, as Michael Phillips writes, it’s the cation exchange capacity (CEC) and percent base saturation that are truly indicative (cf. Part 2 of the calcium series).

The CEC of a soil indicates how porous a soil is nutrient-wise. Our soil is 15.6 MEG/100g. That means that, in every 100 grams of our soil, 15.6 meq of soil can hold onto the goodies, both basic and acidic: calcium (Ca), potassium (K) and magnesium (Mg), that come along in the soil water, as well as hydrogen (H), and sodium (Na ) and aluminum (Al), which are not plant nutrients.  All this also indicates a fine-textured loam to clay soil and that figures with our observations of our soil.

According to Calcium in the Soil, Part 6, the percent base saturation data mean that, of the 15.6 meq that can hold on to cations, 7.9 meq is occupied, or saturated, by calcium (50.6% of 15.6 = 7.9), 1.65 meq by magnesium and 0.64 meq by potassium. So 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). That explains the pH and indicates a fertile, slightly acidic soil. Acidic soils (3.5-6.0) are low in fertility because too much of the CEC is occupied by hydrogen or aluminum. Alkaline soils (8.0-9.0) are oversaturated with calcium and/or magnesium.

The fertility of this soil can be increased by adding organic matter. My soil test didn’t include an organic matter measurement, but it must be low. In any case, before contemplating this, there are more mineral considerations to be had:

  • Ratios of Ca:Mg:K

Magnesium pulls soil closer together, while calcium spreads the particles further apart. Clay soils require higher levels of calcium to improve porosity, thus drainage and aeration. The Ca:Mg ratio for us is 50.6:10, or 5:1. A clay soil that is porous enough and that is balanced (so that enough of each cation is available for plants, not tied up) should have a ratio of 7 or higher to 1.  A 5:1 ratio more resembles the nutrient holding capacity of sandy soil. Something is off here. Now enter potassium (K). According to Phillips, a good  Ca:Mg:K  ratio for clay soils  is 76:10:4-5. Ours is 50.6:10:4.1. The ratio between magnesium to potassium is spot-on for clay soils, but the main player, calcium, again throws it off.

This means one of three things: 1. either our soil lacks the calcium to make it porous, or 2. the levels of magnesium and potassium ares too high, cancelling out the effect of the calcium, or 3. both.  We’ll have to take a closer look at the absolute numbers, which we’ll do below.

  • Recommended absolute levels for macro-nutrients

Phillips’ recommendations for good orchard soil indicate optimal lbs/acre, but my soil test gives me those numbers but in ppm (parts per million). Luckily Phillips addresses this in a footnote (chapter 3, footnote 47 in case you’re curious).  The conversion formula (called the Cornell equivalent) is (Ca in ppm x 0.75) x 2 = Ca in lbs./acre.

CALCIUM. Calcium benefits the fruit’s skin and cell strength, which leads to lower bruising susceptibility, better keeping ability and better pathogenic fungi resistance. Phillips’ bare minimum total Ca for an orchard = 2,000 lbs/acre for a lower-CEC-value soil (below 25 CEC). Ours is 1548 ppm, so 2322 lbs./acre [(1548 ppm x 0.75) x 2].  Our calcium level is good. (The ppm bar chart on the soil test say it is too high – actually, off the charts – but this interpretation was for vegetable garden soil, not for orchards.)

NITROGEN. Phillips explains this so well. Most nitrogen in any soil is locked up in organic form (as protein) and needs to be converted into mineral nitrogen that can be taken up by plants. This conversion start with the protein form of nitrogen being ammonified, and a portion of the ammonified nitrogen can then be nitrified. This is done by bacteria and fungi who constantly immobilize (take up) mineralize (release) it by digesting it and the other soil microorganisms who have absorbed it. In a soil dominated by bacteria, nitrifying bacteria rapidly convert the ammonified nitrogen into nitrates. However, in a fungally dominated soil, the acidic enzymes produced by the fungi will lower the pH, making it unfavorable to nitrifying bacteria.  More of the ammonium therefore remains available. It is this kind of nitrogen (ammonified, not nitrified) that is preferred by woody perennials like berries and fruit trees. Too much soluble nitrogen causes problems with calcium and other mineral uptake. High levels of nitrogen, particularly as nitrate, encourages fungal diseases like powdery mildew and rust, as well as bacterial diseases. That our soil is fungal is indicated by the low level of nitrate (NO3-N) on the soil test, but…

PHOSPHORUS (P).   The right amount of phosphorus determines the nutrient density (Brix) of the fruit as well as root development. Phosphorus too is  a very fungal affair. It is made available by fungi that feed and then die and decompose and delivered to the plant by mycorrhizae. In biologically managed soils, potassium is constantly replenished by the decomposition of organic matter. Phillips recommends phosphate (P2O5) to be at 200 lbs/acre, or P levels at 43 ppm. Our P is only 12 ppm, a marked deficiency in phosphorus. This indicates something wrong with the “fungal machine”  in my soil, no doubt because it was at the time of the test so disturbed and eroded. Phillips writes that getting this phosphate system working is challenging. You kind of have to already have in order to get it. The trick here seems to be organic matter: a good quantity of that with a good population of beneficial fungi in balance with bacteria (brought in by enough, not too much nitrogen) should do the trick. Ha! I will have to do some more research here. Maybe now, after several years of non-disturbance and checked erosion, the phosphate levels are up again?

POTASSIUM (K). Phillips recommends 20o lbs/acre of potash (KO2) or P levels at 83 ppm. Our potassium level is very high at a whopping 243 ppm. As we saw, potassium plays a large role in the cation balancing act. Our high levels of K  are which is reflected in the skewed  Ca:K ratio and the recommended 1:1 to 1:2  ratio for P:K  is also well off.

CONCLUSION. If the new test on the soil on the slope comes back looking like this, then it seems like we will need to bring the Mg and the K down, the P up. The Ca and pH can remain the same.

One recommendation I found was to add gypsum to leach out the excess potassium and magnesium. Gypsum (calcium sulfate) would also up the calcium without changing the pH (which is fine).  It also helps slow the nitrate release of decomposing organic matter. However, Phillips warns that the calcium cation saturation needs to be over 60% before adding gypsum  to lower excess magnesium, otherwise the sulfur in the gypsum will take out the calcium first. Mmm. Then the potassium will need to be increased. Wood ash seems a possible candidate for this: it is 20-30% calcium, with 4% potassium, but only 2%  phosphorus, magnesium, aluminum and sodium. It may, however, increase the pH, and also, because of its potassium content it should be applied only when active growth has engaged, so wood ash could be my liming agent after planting…

A new soil test is in order, because these numbers are just too out of whack for me to make sense of. One thing I know for sure, though: we will also want to add lots of organic matter. That’s where the hugelswales come in. And that’s another post.

A friend came to visit us and after eating homemade Belgian waffles I suggested I take her and my family to Pod Meadow, which I had discovered on a walk with Transition earlier in the week. The weather was a balmy 55F and only partially overcast.

Pod Meadow is an amazing conservation area in my town that is a hidden gem, “a sleeper,” the town naturalist calls it. It is 25 acres. You park the car on a busy road – no less than the old Native American Great Trail, which became a major highway in the colonial era and is now Old Connecticut Path, or Route 126. You walk through someone’s yard, and then, suddenly, this:

Amazing, the sudden dip toward the Pond and the lack of tangled shrubs under the stately trees – mostly beeches, oaks and some pines and spruce – which allows you to see right through. It gives the open and clear feel of a maintained forest, much like, I presume, the forests in the time of the Native Americans, who used to set fire to the underbrush to make hunting and travel easier.

In this forest the maintenance is done by the beavers. I don’t have the skinny on the beavers yet, but there seem to be many of them and, some worry, too many. They have dammed the Pond so that now the water reaches higher, inundating old trails and making what used to be a vernal pool (first water body in the picture above) into a part of the “full-time” pond.

The beavers clear the forest by doing this:

Amie couldn’t believe it. Imagine chewing through a whole tree with your teeth! There is more beaver handy toothsome work behind her: the beavers apparently like beeches the most and in this spot most of them were stripped of their bark at beaver height. It is amazing to run your finger over the scrapings. To me it is like touching the wild. Here’s an even bigger tree (an oak) being worked on:

And some more beeches:

We speculated that there must be some system or plan in their activities. Perhaps they are working up to a moment when they will tip one tree and it will take down all the others, like dominoes, in one great bang! Then they’ll have a party, say “our work is done here,” and move on.

For the moment they’re at home. This is their lodge. No sign of the inhabitants.

Seeing all this is so awesome to me, and I am eager to learn more about these animals. I’m also fascinated by the geology of the place, which is, like so much of New England, dominated by the 50,000-year-old glacier that started to retreat 15,000 to 16,000 years ago. I sometimes dream about that glacier.

Today was about Amie. At first she didn’t want to come but the moment we arrived she started running and jumping, suddenly free and wild herself. She had climbed onto this great downed oak before we knew it and DH had to scramble after her.

She also really wanted to walk on water:

She was upset at the end and I didn’t know why. She said she had “wanted to have more adventures and all we did was walk around and chat!” I will take her back after school some day and she can show me what it is that she wants to do. We can also take our journals and draw or write.

We are reading the Finn Family Moomintroll which another friend gave her and perhaps she has that landscape in mind and the adventures of Moomin and his curious friends. I can certainly understand her. When I was a kid I was always pottering around in the overgrown area (now a nature reservation) across from my parents’ house, pretending to be the last kid left on Earth, losing my boots in the bog, coming home with leaves and mud in my hair.

I would have gone on that tree too! I may still.

John Root conducted an Edible Wild Plants Walk at the organic Lindentree Farm in nearby Lincoln yesterday evening and I was there. I learned that that weed, of which I pulled thousands from the old compost heap, is Lamb’s Quarters, that it is absolutely yummy and nutritious and grew itself for free and without my care or attention (but I already knew that). And I ate not a one. They all went into the (new) compost, though, so eventually I’ll eat them, but still.

The entertaining  and knowledgeable John Root introduces us to Jewelweed

Today I pulled several weeds from the strawberry patch. I spent some time with one of them, Botany in a Day, and Amie’s loupe and discovered it is a Mallow, probably Cheese Mallow (Malva rotundifolia). Here’s the distinctive funnel-shaped five-petaled flower with a column of stamens.

Mallows have 3 to 5 partially united sepals and often several bracts. This one has 5 sepals and 3 bracts (smaller sepal-like modified leaves):

My plants has these beautiful round leaves – hence my hunch that is is rotundi-folia:

The ovary of the Mallow matures as a capsule, or a “cheese”:

Matured flower next to immature flower:

The Mallow is mucilaginous or slimy when crushed and contains pectin. The marshmallow we roast over the fire used to be made from the roots and seeds of the Marshmallow (Althaea officinalis – which comes from Europe and which I purchased and have thriving in my herb garden) and our indigenous Malva can be used to make marshmallow too.

Because the Mallows are so slimy, they are a great external emollient and an internal demulcent and expectorant. Roots, leaves, flowers and seeds (cheeses) can be eaten and are rich in calcium and iron.

I’ve always been fascinated by evolution in all its aspects (or at least those I can comprehend) but, I realize now, for different reasons than some if not most people. Usually people’s  interest in evolution is in a theory of advancement, even perfection. These people reach for the light, like the  plants that developed vascular systems to grow upright, up toward the sun, and left the primitive, non-vascular mosses behind, eventually shading them out.

The Asters, the dandelion among them, will appeal to them. They are some of the most advanced plants in on earth, well-adapted to new circumstances, and newer.

I’m not charmed. The Asters are to me but the first and the least interesting step on a long ladder leading back, down into time. Primitive, that’s what I want to  see. The older, the more fascinating. So, among the flowering plants, I like the buttercups (Ranunculus).  The buttercups are (give or take) at least 34 million years old (*). I am honored to have one of these awesome survivors in my garden.

Now, my buttercup is not nearly as ancient as these guys:

I don’t mean the squash – though the Cucurbitaceae as a family are  even older than the buttercups, originating in the Late Cretaceous, some 60 million years ago (**). I mean the mushroom, as yet unidentified. A mushroom is the fruiting body of a fungus, and fungi like these made landfall in the Cambrian, around 500 million years ago, long before plants did.

These mushrooms are growing, by the looks of it symbiotically, in the bed I fertilized with horse manure last Fall. It is, by the smell and feel of it, my richest bed, but we have mushrooms above ground and mycelium in it (or, I should write, through) it all over our property. It’s nothing to be alarmed about. Almost all plants partner with fungi, and 80% of plants couldn’t survive without them. It was probably this association that made it possible for plants to come ashore in the first place, between 440-510 million years ago.

I’ve found the same combination on some of the seedlings’ peat pots (the pairing here is some other, unidentified fungus, with a pepper seedling).

How awesome is it, to have evolution – time itself – growing right there in your vegetable garden, and to know it, and to be able to tell some of that story.

(*) see here for a marvelous ladder.

(**) more ladders here.

My copy of Botany in a Day by Thomas Elpel arrived yesterday and I am hooked. Clearly written, humorous but without fluff and to the point, tightly structured, and beginning in the beginning and ending with the end. Just the way I like my books on the structure and evolution of plants. I plan to learn a lot!

That’s it for today. Just a plug for this wonderful book.

Every Spring, since we’ve been here, we’ve had a Robin’s nest near the house. That’s why we call the place Robin Hill – plus it has a little bit of Robin Hood in it.

Year One (2008) they chose the rafters of the carport and Year Two they chose the nook next to Year One’s nest. We never understood why they do this, as the carport is a relatively busy place. Each time we would walk in or past, the Robin on duty would take off with a great flutter of wings to perch on a nearby tree branch from which to scold us until we left.

I know that Robins will return ever year but will never re-use a nest, and now it seems that they won’t even use the same space. In anticipation of their return I had moved the two old nests so they could go there again, as they seemed to like it so much. Instead they chose to move into the Japanese Andromeda that is right next to the mudroom entrance and the guest room window. An even busier place!

We now use our other (main) door – which leads straight into the living room – as often as we can, and try to tiptoe around, but it is difficult not to disturb them. The frantic escape from the dense bush is even more alarming what with all the leaves flying off as well. Still, it makes for great observation. Maybe we will install that webcam.

So far there are three beautiful blue eggs in the nest (Robins lay one egg a day and usually stop at four) — ah, that was based on my quick peek yesterday: today there are four!

And one wary Momma Robin (it’s usually the females who incubate the eggs).

There must be a bird’s nest in our shed as well. Each time we walk in there is a loud chirping, but we haven’t located it yet, so I can’t say what it is. Maybe the wrens, who always hang out in that shed.

The other night my birdwatching neighbor came over to tell me there are is Barred Owl (Strix Varia) nesting in the trees behind our property and that I should listen for its calls. That evening, there it was, that typical “Who Cooks For You” call. By the time we got the mike out there, the call had changed to:

owlhoot1 and owlhoot2

(We are thinking of placing a mike on top of our roof, and whenever we hear something – the fisher cat, or the owls – we plug it into a laptop and record it. Yet another scheme here on our Hill!)

As we listened that evening I said to DH how wild it was, how I love how wild this place is (I wrote about the contrast with Europe here). DH remarked that surely an owl is not that wild – maybe he had jaguars in mind, and grizzly bears.

I replied an owl is pretty wild. What do I mean by wild, or wilderness? It took me not a second to answer it: Wild is Old.

That owl up there, high up in the tree, in the wind and the total darkness, is calling for a mate as it has been calling, with that exact same call, for millions of years.

Compare this with us, humans, our many, many languages, our many more ways of wooing, of saying “I want you” and “here I am”. And we’re changing  those every thousand years, every generation, every day. We are constantly adapting, transforming, cultivating, culturing.

The owls, the fisher cats, the bees, they don’t change. They stay wild. Their wild ways work for them as they did millions of years ago. That is wild. Wild is Old.

I heard the sound again and this time we ran out to record it. It was further away and it sounded a little different from last time – less catlike – but though the “words” are different, the voice seems the same (to the one in my memory). In any case, if you can tell us what it is, if not a fisher cat, let us know!

animalsound

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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!