CEC Base Sat lab AUDIO

Added: 2026-05-12

[00:00:01]okay so in this lab demonstration i want to go over uh two tests that we would look at things we look at in a soil test we've already discussed cation exchange so cec but what i want to talk about is base saturation as well so i'm going to introduce you to that concept um so this picture down here will sort of be reminiscent of what we talked about with the cation exchange the idea that positive ions are attracted to negative charges on the soil surface what base saturation does is it basically looks at what is currently stuck on your soil so if you send in this soil clump that's in this picture let's say you just bought that clump and you put in a bag and you sent it off to the lab they're going to uh expose that clump to an acid and they're going to knock off whatever is there right so things like calcium potassium and they're all going to end up in a in a beaker right all of them floating around in there and then they're going to use probes and tests to measure each individual element and they'll find out how much magnesium is in there how much calcium much potassium etc and that gives them a snapshot of what is actually on your soil not in it in terms of the water solution that's around it but what is on your soil that's the base saturation so if there's 24 negative charges and half of those charges are occupied by a calcium then it's 25 or 50 calcium based saturation okay um on the non-audio link this video here will this video link will work to take you to something that will help you explain understand that in the extra content folder i've got two videos by ag phd a couple of kind of goofy academic farmer types but they do really good videos and they do a very good explanation of what they're talking about uh whether it comes to cation exchange capacity and base saturation so there are some target ranges that are ideal so for calcium you're looking at quite a bit occupying the spaces in your soil on your charge charged surfaces so 65 to 80 percent is calcium uh and then when you're looking at magnesium 12 to 25 magnesium on your base saturation and then potassium and then 10 or less with hydrogen uh why would we want hydrogen hydrogen's an acid and by having some of the charges on your surface being occupied by protons means your soil will buffer the ph a little bit it's got some reserve in it um which is a good thing if it was a hundred percent topped up you wouldn't be able to add anything to the soil it would just leach away so we want to make sure there's some available spots if you do watch the videos which i hope you do with ag phd they'll get into this but i'll just briefly explain to you one thing calcium magnesium are major nutrients when it comes to soil charged surfaces and they have not only are they a nutrient but they have physical effects on the soil calcium is a very large atom so think of it as a giant beach ball and magnesium is a very small atom like a little silk grain very different size i know often we don't really think about atoms being different sizes but they are and when there's lots of calcium in soil those large atoms actually open up the soil and improve its porosity so water drains through it better it gets better aeration when you have lots of magnesium in soil because it's small it helps pull the particles closer together uh making the water the soil waterlogged and less prone to drainage and then you end up with less oxygen so an interesting trick that farmers have learned over the years is that by adding uh to soil that's that's not draining well by adding a good dose of calcium to the soil it fixes a nutrient problem that's out of balance and it loosens up the soil and to give you a personal example uh a relative of mine drills uh water wells for a living and other kinds of wells sampling wells and stuff but um and oftentimes when you're drilling you come to like a heavy clay section and the bit doesn't push through that easily it gets it gets plugged up and it's a hard it's a lot of work to get through that layer to keep drilling deeper for water and what they do in the drilling industry is just like what we just talked about they pull the bit back and they dump calcium chloride down the hole and the calcium reacts with the clay particles opens them up and the knife or the drill will actually drill through the section like butter within a matter of minutes that's how quick the reaction is so calcium opens up soils makes them more porous magnesium makes them really tight so if you get a base saturation analysis and the data comes back and shows that you have more than 25 magnesium in your soil you may have a tight soil that's not going to drain very well and you're likely not to have enough calcium for your plants so this slide is obviously very small so let's this is a soil analysis that we did on college uh rhododendrons at different areas and you'll notice down here it's clay loam sandy clay loam loam and loam so these are different sections of the can of the college campus if we zoom in to over here you'll see on this column it's cation exchange capacity cec right so that's your total capacity and then over here we have our base saturation or cation saturation and uh what's interesting is looking at these numbers we've got uh one one and a half point four one point two point six percent of potassium where potassium is supposed to be in the four to eight so see if i can write this four to eight percent so potassium is a little bit low um magnesium on the other hand is fairly high we have some that some two soil samples that are ones at 29 and a half and the other one's all the way up to 37 where usually it's no more than 25 magnesium right so we have a problem there um calcium looking at calcium at 25.9 23.3 31.9 what is calcium normally we want normally 65 to 80. i'm getting better at writing with my mouse by the way i don't know if you noticed that 65 to 80 calcium so we're way low in the calcium here so these plants are going to be having some problems and then hydrogen remember that's the buffering capacity the ability of the soil to store more nutrients it's like free parking spots with little pylons holding that spot uh they're all the way up at 50 54 there's a lot of unused space in that soil it needs some nutrients and what does it need it needs a little bit of potassium but it definitely needs calcium so one of the simplest things you can do in this context is add lime so what does lime do okay so lime is calcium carbonate that's this molecule here calcium and a carbonate molecule they react with hydrogen remember those are those h's on your soil and they react and form different things the calcium is released co2 bubbles out into the water this is basically like adding baking soda to your cake when you add it the co2 is formed from the instead of calcium it's sodium carbonate or bicarbonate and the co2 forms bubbles which makes your cake rise and so in soil when you add lime calcium is released it binds to the sites that were occupied by the hydrogens and the hydrogens are turned into water because they react with oxygen and the rest of the carbonate is turned into carbon dioxide so there's a chemical reaction that happens in the soil and the benefit which you have to remember you don't have to remember the chemistry per se but the major benefit is that by adding lime we add calcium to the soil we consume some of the acidity right so we're affecting ph and we are impacting base saturation so um so here again how was removing hydrogen from soil colloids helpful remember i said they're kind of like a parking spot like a pylon right so this is sitting here not doing anything if i add lime boom i consume the protons and i replace them with calcium but if we remove all of them then our soil has not got a lot of buffering capacity so but it it you know it doesn't have to be that thought through um but basically adding lime uh is a very useful thing especially the soils that are not draining very well and are showing calcium deficiencies so we raise the ph of the soil because we have fewer protons present right so we're dealing if we're dealing with an acidic soil so there's that we add calcium we talked about that we increased the availability of charge sites by consuming protons allowing soils to better buffer ph so for example sandy soils which have very poor cation exchange and base saturation their ph changes rapidly and farmers really struggle to keep this is the root zone at a happy ph uh where heavy organic soils tend to buffer their ph and they're much more stable because they have far more cation exchange capacity so if you have a sandy or soil this is a much more important exercise for you all right uh there's a couple of scenarios that are coming up i'm going to do separate videos and insert them all between these slides [Music] and that will help me do what you would have done in the lab which is sort of demonstrate them with little simple models but hopefully this is helpful okay so i've got two sponges here with some wooden kebab sticks in them and uh i'm gonna sound repetitive some students are gonna get this right away and some are going to be confused so i want to go through this over and over again to make sure you all get it essentially each of these sponges represents a soil colloid it could be a piece of clay or it could be a piece of organic matter a chunk of compost this soil demonstrates a soil particle that has very poor cation exchange each of these spikes represents a potential uh site where a cation could bind so this is a negative charge negative charge negative charge so calcium could bind here here or here or potassium can go here here and here whereas this soil which represents a high cation exchange capacity soil has lots of negative charges on the surface and it can bind lots of potassium calcium magnesium okay so this is an example of a high cec soil and a low cec soil okay so in another lab scenario uh i'm supposed to demonstrate what it would look like if you were taking a low cec soil like this sponge so it's got very poor cation exchange capacity and we want to increase it and so using the exact same sponge i'm looking lazy here but really it works we can add humus so by adding compost into the soil boom now we have our regular soil particles and what we've added and look at that we're happy we've got lots of cannon exchange capacity so by adding compost or biochar we have improved the cation exchange capacity of this soil okay so before after my okay the next lab scenario says we're supposed to demonstrate what a salt would look like if it had 50 potassium 50 calcium based saturation so what i've got here is i've got one two three four oops and one two three four let's say the yellow is calcium and the green is potassium we have 50 of the available charges that's each stick represents a charge 50 percent are calcium and 50 pounds potassium i don't know if we got those colors reversed but i think you get the idea okay so if we take this soil sample to a lab they're going to wash it with acid which is going to knock everything off the soil into a beaker right then they're going to go into the beaker and they're going to count out how many of each was in the soil and they'll say there's four of the potassium four of the calcium our base saturation is 50 potassium 50 calcium okay so that's what how base saturation works that's kind of what it looks like okay in this other lab scenario we're supposed to demonstrate what happens when you treat a soil with lime in this case calcitic lime so calcium carbonate in my sample soil here i've got a calcium a calcium potassium potassium potassium and i have one two three four sites that are just negative charges with hydrogens attracted we can't see them i don't have a color let's say there's one two three four hydrogens that are binding those negative sites you won't ever have a negative site by itself it's always gonna have something attracted to it and it's always gonna be a hydrogen if you don't have any of the cations around so along comes our calcium carbonate in the water right it reacts with each hydrogen so let's say it reacts with this one it's going to take it off and it's going to replace it with the calcium and this hydrogen is going to turn into carbon dioxide and water and be gone and then another calcium carbon is going to come along and it's going to remove that hydrogen and replace it with the calcium and we're going to release release water and carbon dioxide another one's going to come along it's going to take up this hydrogen right and it's going to release water and carbon dioxide and another calcium carbonate is going to come along and it's going to take this hydrogen oh and it's going to leave water molecule and carbon dioxide are going to disappear and you're left with soil that has much more calcium attached to the negative charge surfaces and far fewer protons in this case i removed all of them okay so that's what happens when we add lime okay so i've devised a little experiment to demonstrate cat on exchange capacity and what we've done here is this is standard peat moss uh your high porosity mix with your bit of perlite in it around 20 perlite and i've taken that and i've mixed it 50 with vermiculite this is a bag of horticultural vermiculite uh bought at a garden center uh if you look at vermiculite under a microscope it looks a lot like clay there's lots of thin layered sheets of mica vermiculite is usually added to soil to hold water so it's put over top seedlings to keep them from drying out at the surface you don't have to irrigate them as much which disturbs the soil it's used for seedling mix again to have consistent moisture levels uh it's also used in soil mixes where you are worried about water loss uh so crops that are really sensitive it's expensive so you don't often seen it used you don't often see it used in uh broader production like oh it's a a plant that needs to be kept wet there's other ways using detergents and stuff which we'll talk about another time but vermiculite is available in high value things like seeds and plugs it is used um but one of the properties of vermiculite is because it's these thin sheets of mica is that they have lots of negative charges so i have over here let me turn my meter on this is i'm going to do a pour through analysis here this is my fertilizer solution that is sitting at an ec of 4.5 so let's set this aside and let's water in the standard porosity mix i've given it i'm gonna go halfway okay and then i'm gonna go halfway with this not quite all right i did a little bit more in the vermiculite one all right so we're gonna let them do a pour through and we'll see what comes out the other side if the vermiculite has enhanced uh cec less salt is going to come out the other side of the pot right because the negative charges are going to hold on to all the cations that are in the fertilizer solution so just take this off let's pour some water through okay the next one there's a little coming out for my excess but that's okay we're going to do a pour through on what the soil is holding i don't really want necessarily with the volumes holding so let's wake this up take the sample off and measure the ec what came out the other side and lo and behold what came out the other side was 4.5 exactly what we put in okay i'm going to dump this into here and maybe to try to be a little bit empirical we'll give this a bit of a rinse dump it there i'm gonna give my probe a bit of a rinse okay let's put this here and let's this really could be a lot more empirical but you get the gist okay let's get our probe in here and the ec three and ec of three if you don't believe me i don't know if you can see it on there but i'm not lying an ec of three so what's happened is the vermiculite has held on to those cations in the fertilizer solution now the anions will continue right on through so you're going to get some higher salt levels but what we've done here is we've improved the cation exchange capacity of pmos by adding vermiculite hope you found that helpful