Aeration and Irrigation W20

Added: 2026-05-09

[00:00:00]hi everyone thought I'd show my face one more times it's just a voice but anyways I do a little bit of review and then build on what we covered in the last lesson so right back to the first lesson we talked about the acronym clerked and what we call soil formation factors so things like climate organic matter or organisms relief which is the topography of the land so if it's steep and rocky or a flat plane that we talked about parent material and I have to sneeze I'm allergic to everything at this time of the year anyways parent material yes so the type of rock that makes up the mineral soil that makes up so much of our soil so the parent material that has made our rock has a big influence on the chemistry like pH so remember granite bedrock is acidic where limestone bedrock is basic as we move later into the course into nutrients the pH will make more sense to you but basically a different pH as different nutrients are more available so that type of soil can be helpful or not and we did talk about potato scab as an example in PEI soil where we don't get the disease because the acidity inhibits the germination of these spores that caused that disease so it sort of breaks the disease triangle and lastly there's time right so remember it takes a few hundred years for a couple of millimeters of organic soil and thousands of years for a fraction of a millimeter of inorganic soil so when you think about it like that you realize how precious soil is and why we don't want to lose it through erosion especially off our fields or producing food I reviewing the terms alleviation and alleviation right so aloo VA means for particles to wash down into the soil and the eluvian zone is where they arrive right and of course the eluvian zone the depth of the Aleutians own depends on the amount of precipitation that's in that particular geographical location so in a tropical country fine particles are alleviated further down sometimes out of the reach of roots meaning that what's left is not as nutritious so those finer particles that are carrying the nutrients are far down below and then in a semi arid semi-arid location the eluvian zone is somewhat higher so let's take grassy plains and stuff like that and then in a desert where there's almost no precipitation the eluvian zones right near the surface but the roots are shallow and there's not a lot of depth so the plants and species that normally grow in these types of soils have adapted to these conditions but sometimes humans come along and we want to do something and we forget that the soil underneath is very different so all right then in your lab you explored forces that act on water and soil specifically adhesion cohesion which combined together make capillary forces which help pull water into tight spaces which is what keeps water up in the soil and then we talked about gravity or gravitational water which is what's pulling out of the soil your lab today builds on this where we measure things like field capacity and saturation so the idea here is that we take a volume of soil and we completely saturated with water so that all the air spaces are fully occupied with water right that's saturation after you let gravity drain the gravitational water out and ever stuck by Kepler action is left that is our ideal starting point that's the field capacity of the water that's how much the field can effectively hold in this context there's none of oxygen so plants are going to die but of course if you've just watered your plants that's fine but if the water stays like that for more than a few hours then we have problems there's a video in this week's folder drainage issues with farming then it goes into how field drainage has a big impact on yield and production so I encourage you to watch that alright so let's move into today where we deal with air and water and soil excuse me okay porosity aeration macro pores micro pores these are things we covered in the lab on Thursday of last week and I want to build on those so the amount of open spaces between soil particles which collectively are the micro pores in macro pores we call that porosity right so sometimes you'll see soil being sold that says high porosity so it's got coarser particles which leaves empty spaces for air to accumulate so water will drain out that's because these spaces are too far apart for water to suspend itself across them with adhesion and cohesion as your soil becomes less porous water is able to span those locations and it doesn't drain as well and they get less oxygen so we have large macro pores and we have small micro pores right so remember the video I showed with the screens that's what I was demonstrating there and then here's that review slide showing capillary action how to pulls water into tight spaces I know I'm repeating myself but you know you know what they say about repetition at least it worked for me to some extent and themself a bad memory but it helps again here's a cross-section of some soil realistically soil is an amalgam of lots of different sized particles so here you may have a sand a large sand particle some finer silty smaller sand particles and then voids where there's air spaces so altogether these these things come together to impact the porosity of the soil so a sandy soil versus a clay soil so the macro pores and micro pores those the key terms you need to remember so how does that impact field capacity well there's a lot more open spaces in the large macro pores and not a lot of open spaces in the micro pores so you might say well there's more capacity in this one but is there it's hard to say because what happens is have you as you saturate this the water freely drains out so a lot of it is lost down into the soil whereas with the micro pore or the low porosity soil there's lots of tiny spaces which means the water is trapped in here so maybe there's a higher water holding capacity this is a bit of a fuzzy science there is no perfect situation and what you'll find whoops what you'll find is that most soils that are a mixture of particles end up being the best compromise so again open spaces contribute to porosity that's our micro pores and macro pores so typically the macro pores is where we get our air and our micro pores is where we hold water and so we want a combination of those both together to have a soil that will support root growth so the amount of open spaces between the soil particles gives us both water holding and air this looks like marshmallows and potato chips all right so we've got parati but what else is there right there's air so let's again review that right so our total porosity is measured by saturating with water so all pores are occupied with water that gives us a measurement of all the pore space and then of course after we let it drain right after we let it drain we're left with our total aeration so in today's lab we're measuring the different volumes so we're measuring how much water goes into the soil before it's saturated and then after draining it whatever comes out whatever drains out this volume here equals the total of all the air spaces that are left so we can measure the total aeration capacity of a particular soil sample by measuring what drained out of the macro pores right that gives us an idea of how much oxygen or air the soil can hold so again we've got total porosity which is all pores occupied by water and then we measure what drains out and through subtraction we get our total aeration so the trade-off which of course is logical is we also have water holding capacity so if we have porosity and the air spaces that are left obviously some water is still in the soil after it's drained and that's what we call field capacity so this is where it's a teeter-totter or a balancing act because we obviously want oxygen for the roots to grow but we also need water and if we have soil that won't hold the water at all then we're constantly irrigating and also constantly leeching our nutrients away from the root zone so we need a balance we need this sort of ideal soil this is where that same need low comes in right soils that have a really good compromise between porosity and aeration and field capacity looking at peat moss this is one of the reasons why commercial ornamental growers like to grow a pot of plants in peat moss I like to use the analogy of shoelaces in a bowl so here's my bowl full of shoelaces if you look at a low magnification there's always sort of chunks with air in between like that that's the macro pores but if we zoom in right zoom in here zoom in here and zoom in again you'll see that each of these whoops each of these strands that I highlighted these strands here actually are made up of lots of micro pores so water wicks into the shoelace right all these pores are occupied with water but air occupies these macro pore spaces and there's lots of them because it's spongy so we have that balance between water holding capacity down here and total aeration in all these macro pores so that's what makes peat moss so suitable for ornamental growing kind of the flipside of the same story looking at the the back side of total porosity is bulk density right so that's the dry weight by a volume so that's how dense a particular soil is so so this example silt loam soil has a bulk density of 1.3 3 grams per milliliter or a cubic centimeter so as an aside basically if we have rock remember soil starts as rock that's about as dense as it gets on average 2.6 5 grams per millimeter per milliliter so that means that silt loam has a bulk density of around half the pores of 50 percent of it is pore space compared to the original rock configuration that it had that's not only air that's just total prosody right so bulk densities kind of like the flipside of porosity so it's it gives us an indication of compaction some soils are denser and as a reserve result will hold more water others less so or some soils are more prone to compaction which results in more water holding capacity and less oxygen stored so you think of places where tractors are driving causing compaction those are also difficult for roots to penetrate so some roots are very fine and have difficulty penetrating dense soils I again drainage plays into this which is why I suggested you watch that video and this picture here we have a field that's got a huge amount of water that's standing and water in the field is a big problem first of all it displaces air right so we lose our air which means that anything that's alive in this wet area dies unless it's an anaerobic organism but most of the beneficial organisms we want are air-breathing so aerobic bacteria the little animals that are part of the cycle that release nutrients they all die in these wet areas and worse yet the type of bacteria that thrive in wet soils will take our fertilizer specifically nitrogen and they'll convert it to nitrogen gas right soon and to which then evaporates out of our soil and is gone and lost to the atmosphere which if you look carefully the plants are yellow on the fringe obviously the plants die in the wet spot but all around these wet areas the plants go yellow because they can't get enough nitrogen because the bacteria are busy converting that nitrogen back into nitrogen gas so yeah poor drainage has costly consequences so drainage is a big big deal in landscaping we put efforts into creating drains in farms we put drainage into our fields this is where I was talking about last class about textural boundary layers right so remember we have our our fine soil like say our sandy loam and then a coarse layer underneath it that creates that textural boundary which holds the water up in the soil so the plants could benefit from it but when you have a big rainstorm or anything that excess water is allowed to leak through into the textural boundary layer where it collects in a drain and is taken away so textural boundary layers are really useful tools and drainage because the act does a check valve so in the case of that field we just looked at when it's saturated the water will will leak out of the top soil into the drain area and be taken away so what are the advantages of drainage well it improves aeration because we're getting water out of the soil right gravitational water is gone I saw warms up more quickly in spring this is another interesting one some farmers and commercial gardeners will find that the earlier they get in the soil the better we have a fairly short growing season in Ontario and it's really important that you get going as quickly as possible to make sure your crop finishes in time for full harvest and when your soil is wet it takes longer to warm up because water has a high heat capacity so the better drained soil is the quicker it warms up the quicker your seeds will germinate and the quicker your crops will grow so from an economic standpoint drainage makes a big deal it's has a big impact on your your profitability lastly there's structural implications for drainage right there's some landscapers in our course so we should for sure pay attention to this if we don't drain our soil properly when it freezes it pushes things up like posts and fence and decks even structures get shifted around so proper drainage right that's weeping tiles around the perimeter of a building they take the water away so in the winter it's not freezing heaving the structure up so again waterlogged fields have lower yields because of anaerobic that's low oxygen conditions which contributes to disease and also buildup of salts and the loss of nutrients like nitrogen this is showing salt buildup in soil so sometimes like some nutrients the bacteria can't do anything with and so they accumulate and things like sodium will actually leech up into the soil while others are gone and you end up with really salty soil that won't support plant growth at all that's all around a bad thing so different methods of drainage we've got ditches grass waterways if you remember my first lesson I talked about the Holland Marsh and how they dug swales all around it to drain the marsh and leaving that really nice nutritious muck behind that grows all those fantastic vegetables so things like erosion are controlled and we don't end up with anaerobic conditions so good drainage is critical to a healthy plant talking next about irrigation we've done we've discussed the irrigate water in the soil now I want to talk about making sure that we irrigate our crops properly this is an interesting picture over here I don't know if any of you had the privilege of flying over Arizona on the way to California but there are green circles in the middle of the desert and these are all irrigation boom circles right so on the right here we have an irrigation boom and it travels around in a circle and irrigates the soil and it's a desert in that part of the United States but because of irrigation they're able to produce a ton of stuff like lettuce and strawberries and you name it there are definitely implications for bringing water to the desert to grow the soil is very porous so a lot of the water drains away also there's the issue of evaporation because it's hot and dry so more than half the water they apply is lost through evaporation in the atmosphere then there's ethical issues like where do they get the water from right and most of the water is piped in from the coastal areas of California to irrigate these crops and every year there's a push by the Americans the southern states to build a water pipeline just like an oil pipeline from the Great Lakes down to Arizona so that they can irrigate their crops but of course it looks like we have lots of water in our Great Lakes but if our Great Lakes fluctuate by more than a foot or two there's huge problems for both ecosystem and our economics in recent years we've experienced high levels but there's also been low levels and we can't just pump water out of it but it's also a really important part of our watershed so the Great Lakes Commission that oversees our like our Lakes sort of fins them off every year and says no go away and they have a big fight and then it's gone for another year but as our climate changes this will become more and more of an issue because at some point food production is going to trump you know ecosystems I hope not but I suppose if lots of people are struggling to eat then things will change other options aside from field booms are trickle right so we got a pipe with little holes that dribble out you can see the wet spots where each drip part is in outdoor production and drip tapes are very popular because they're low costs sometimes you see irrigation furrows where they let water run down a furrow and it just sort of East it seeps into the soil beside each trough and sometimes of a plow that blocks these off and they'll go along and they'll open it and let water in or these have a header pipe and it just slowly runs down or in a greenhouse we have drip lines which feed each individual plant correctly with with water you've seen a lot of these before so nothing really new in last class I mentioned sub-irrigation or Evan flow where we use capillary action for water to be taken up from below right so flood floors and flood tables I mentioned this briefly in one another lesson but I want to bring it around again this idea that how the water behaves in the soil the plume is important to think about when it comes to irrigating so in clay soils water tends to be drawn sideways rapidly through capillary action and in sandy soils water goes straight down we're in sort of your moderate soils you have a good balance of gravitational forces pulling it deeper and capillary actions pulling it across why do I bring this up well there are certain crops for example commercial cannabis where they grow large plants in large pots and things like peat moss and oops trying to erase and these large pots have to have more than one dripper because peat moss is very porous which means gravitational water goes straight down faster than it moves left to right so if you have a large pot let's say this is your pot and you have one dripper well look what's happening here all this soil over here won't be getting water just where the dripper is right here so by having multiple drippers we can irrigate evenly across the width of the pot so that's something you have to experiment with by trying your irrigation and then digging down in the soil and seeing what got wet and what didn't there are also other tactics where you can give a small shot of water right so a little bit of water doesn't have a lot of gravitational force so it will go down but then you stop and then it will seep sideways and then after a period of time you start again and it will go a little further and then you stop and it will seep sideways so by pulsing your drippers you can also irrigate a why volume of soil so there's different tactics you know if you have a lot of water you could have lots of drippers but if you have a limitation of water so you've only got so much supplied you have to irrigate lots of crops you can use short shots with gaps between and cover a larger crop area and water more evenly now of course you want to make sure you're done within a reasonable amount of time if it takes you the whole day to irrigate that's no good because then your soil is really wet going into the evening typically you want to get your water in the soil before 10:00 a.m. all your irrigating done so that the plants can benefit from that for the majority of the day and not be suffocating when they're actively growing the most which would be you know between ten and three o'clock in the afternoon well they're doing a lot of photosynthesis so yeah texture covered that all right this is a picture of an orange grove and oranges are grown in really sandy soils I don't know if you can see that in this picture but this is basically Sam this is Florida very sandy porous soil so how do you irrigate this it's a hot climate really porous soil so you can use drip lines right with emitters under the trees and try to stick to the shade there the drip line of the tree so that's where the Sun Shade the shadow of the tree would be and drip irrigate each crop now recognizing the water will go straight down you got a mute pulses now what about a vineyard this is a heavy clay soil what do you do with this well some extent it's a bit of a trick question because clay soils very low porosity which means it has very high water holding capacity which means you're not going to irrigate you rarely see drip lines in a grape field growing in heavy soil because there's no need to it's not going to give up its water that capillary force is so strong it's gonna hold it not to mention grapes have very deep roots so it's very strange to see irrigation in a grape crop alright so summary here we talked about drainage methods both surface surface with furrows and swales and ground tiles we talked about the advantages of drainage right so improved aeration soils warm more quickly it protects structural foundations we talked about irrigation methods surface overhead drip and sub irrigation we covered wetting patterns how they differ right how water moves in the soil how to infiltrates depends on the texture with fine textured or clay textured soils we have lots of capillary action moving the water sideways with Sandy high porosity we have water moving down deep we talked about water and nutrient conservation right so the idea that water evaporates from soils we need to make sure that we don't irrigate at the wrong time and also don't lose our irrigation water to evaporation and then of course soil aeration is related to compaction or or the density of the soil so bulk density we talked a little bit about so in the lab today you're going to have a look this is an experiment you're gonna I'm going to do for you but I'm just going to do the experiment and present the results you're welcome to attempt this at home and then there is a lab report you have to write up about the results so I'll tabulate the results post them show you the video of me doing the experiment and then you write the lab report up as if you done it or do the experiment yourself if you are able to which is perfectly fine and present your results I'm obviously I'm not gonna mark the this particular lab based on your results I just want to see you write up the lab based on the structure I outlined and do your your best job nice and neat follow the format proper you'll be just fine give you good marks so we're looking at porosity so we're gonna be looking at total porosity and calculating our aeration porosity and capillary porosity in the lab so comparing soils measuring that up so we're gonna do it for non compacted sample and then we're gonna repeat it after compacting it so what is compacting do it's gonna crush those macro pores into micro pores so it's going to change soil property this is like your tractor driving down a roll and compressing the soil right it's gonna alter the soils properties which impacts its water holding capacity its aeration porosity impacts a lot so the format is introduction methods results and conclusions I don't need references for this not too particular about that but I definitely want you to outline the introduction methods and then the conclusion the methods part you don't have to spend a lot of time on you can say as instructed if you want to highlight something that's fine but the results and conclusions are important and if the conclusions don't quite match your expectations I want you to try to formulate an explanation like Oh Derek did this part wrong or when I did this experiment I drop something or whatever although if you do drop something you probably should repeat it all right