Acidity In The Soil - Kitchen Garden

UnitYear levels5–6Acidity in the SoilCurriculum LinksScience The growth and survival of living things areaffected by the physical conditions of theirenvironment (ACSSU094).Scientific knowledge is used to informpersonal and community decisions(ACSHE217).With guidance, pose questions to clarifypractical problems or inform a scientificinvestigation, and predict what the findingsof an investigation might be (ACSIS231).About this activitySoil testing is very popular in Kitchen Garden Schools, and it isenormously useful in the garden – not just for planning whereplants will go, but also to involve students in an understanding ofthe needs of plants and the reasons behind our treatment of thesoil (with compost and other additives such as lime). It goes a smallway towards explaining why some plants love to grow together andothers won’t tolerate the same conditions. You can even explain tostudents why we don’t put citrus and onions into our worm farms,using a basic understanding of pH levels to show that these areacidic items that make worms uncomfortable .Demonstrating pH levels in substancesMany people have heard of this pH demonstration using redcabbage water, but have put it aside as ‘too hard’. Do try it! It reallyis easy – particularly if you have bits of red cabbage from the garden– and it is lots of fun. As with any experiment, try it out first onyour own; it’s easy to do at home or in the kitchen, and doesn’t needspecial equipment.See the notes in Lesson 3 about which substances to try testingso that you get a full range from acid to alkaline. Test a variety ofsubstances but don’t forget to test the soil from your garden, plusperhaps your compost bins, the worm farm and even under specificplants (label the samples, e.g. ‘Under the rhubarb’, ‘Under thebanana tree’, ‘Chicken coop’, ‘Wet compost, middle bin’ and so on .)and allow time for the sediment to settle.You can use the demonstration to lead to a discussion about acidity,alkalinity and pH levels in the soil, the requirements of plants orthe way our taste buds sense acidic foods (vinegar, lemon juice –very sour!) as opposed to alkaline foods (chalky substances – softand sweetish). When testing the soil using this method, you couldcheck your findings against the results of one of the readily availablecommercial soil testing kits on the market.Several Kitchen Garden Schools have told us that they get the bestvalue out of the activity when they introduce it with questioningand discussion with the class first – because once the students seethe change in colours in the solutions, it’s a little hard to bring themback to thinking about plants for a few minutes! Stephanie Alexander Kitchen Garden Foundation 2011 (except where otherwise indicated).You may copy and communicate this material for non-commercial and educational purposes provided you retain all acknowledgements provided with the material.

Acidity in the Soil Lesson 1Discussion IdeasYear levels 5–6Curriculum LinksScience The growth and survival ofliving things are affected bythe physical conditions of theirenvironment (ACSSU094).Scientific knowledge isused to inform personaland community decisions(ACSHE217).LocationThe kitchen or the classroomDuration:15 minutesGetting started acid/acidicbase/basichydrationneutral pH scalesolutionsubstancetrace elementsRevisit the basic needs of plants: sunshine for energy, water for hydration,soil for nutrients.Our own experiencesVocabularyalkali/alkalineTo start, you might discuss how we, as gardeners, try to create the idealenvironment for our plants to ensure that they grow well. Discuss how smart gardeners recognise these different needs and adjust thewater, soil and sunshine (sun/shade) to suit the plants they want to grow.Collect students’ experiences and examples of things we have done to alterthe soil in our garden (such as adding compost and spreading mulch, chickenpoo or lime).You could also discuss taste as a way of introducing acids.Ask students to give examples of foods that taste bitter, salty, sweet and sour.Can they name some sour foods (lemon juice, vinegar and dishes with theseingredients such as salad dressings)? These foods are acids.What do we know about acids? Can we name any other acids? Which recipeshave we used acids in, and why do you think we used them? (Sometimes acidis used for the sour flavour and sometimes to take advantage of the way itemulsifies with oils, like olive oil and vinegar shaken vigorously together in adressing. It can also be used in a marinade to break down and help tenderiseingredients such as meat or fish.)The opposite to acidic substances are alkaline substances, sometimes calledalkali or base substances.Alkaline substances often taste chalky, mealy and sweet. Do students know ofanything alkaline? It’s hard to think of ingredients, but bicarbonate of soda isvery alkaline (you don’t want to taste it as it’s too strong to be pleasant).Create a class list of vocabulary and examples as you go.Extensions / VariationsHave the students look at gardening reference material, such as books or theGardening Australia website (www.abc.net.au/gardening). Search for ‘acid soil’ and also for ‘alkaline soil’, and plants that prefer oneor the other.Do any of the plants mentioned grow in our garden?If they do, does this tell us anything about how and why we grow particularplants together?What does this make students think about plant families?What do we do to adjust the soil acidity to suit our plants? (Such as addinglime for some plants; compost or manures for others.)Students may extend this concept in part by exploring crop rotation. Stephanie Alexander Kitchen Garden Foundation 2011 (except where otherwise indicated).You may copy and communicate this material for non-commercial and educational purposes provided you retain all acknowledgements provided with the material.

Acidity in the Soil Teacher ResourceThe pH scaleThe pH scale is an international standard that has been tested and agreed on. Having a standardmeasurement of acidity enables us to talk about acidity or alkalinity of substances in a consistent way.The name pH refers to ‘potential Hydrogen’ or ‘power of Hydrogen’ – which means that it is ameasure of the number of hydrogen ions.The scale runs from very acidic at 0 to very alkaline at 14. Neutral water is at 7 – this is a measure ofpure water (but most of our tap water has traces in it that shift the pH slightly, nearer to 6).The pH (potential Hydrogen) scaleConcentration of hydrogen ionscompared to distilled waterpH ratingSample substances at this level10 000 000pH 0battery acid, hydrochloric acid1 000 000pH 1sulphuric acid100 000pH 2lemon juice, vinegar10 000pH 3orange juice, fizzy drinks1000pH 4tomato juice100pH 5bananas, healthy lake water, coffee10pH 6milk, urine, saliva1pH 7pure water1/10pH 8sea water, eggs1/100pH 9bicarbonate of soda1/1000pH 10milk of magnesia1/ 10 000pH 11ammonia1/ 100 000pH 12soapy water1/ 1 000 000pH 13bleach, oven cleaner1/10 000 000pH 14liquid drain cleaner Stephanie Alexander Kitchen Garden Foundation 2011 (except where otherwise indicated).You may copy and communicate this material for non-commercial and educational purposes provided you retain all acknowledgements provided with the material.

Acidity in the Soil Lesson 2Soil Health and pH LevelsYear levels 5–6Curriculum LinksGetting started Science The growth and survival ofliving things are affected bythe physical conditions of theirenvironment (ACSSU094).Scientific knowledge isused to inform personaland community decisions(ACSHE217).LocationThe kitchen or the classroomDuration:15 minutesWhy does pH matter?d,When the soil is too acierothtodsbinsorusphphoywaainlelements in the soitsroontplatsventhat preneedfrom taking it in. Plants’t getcanytheandphosphorus,ethingsomtockstuisitenit whpenselse. The same thing haptthantsmeeleceto other trat is toothalsoisod,neentspla.acidic starves the plantssAcidic soil also inhibitt ideallythaiaterbacialeficbenrootsnt’splagrow around thefixtontplathepand helnitrogen in the soil.These little changes canlowmake a healthy plant yelle toand weak, and susceptibts.pesdiseases andRevisit the class list of activities and vocabulary from the previous lesson.If students looked up acid-loving and alkaline (lime-loving) plants, discusstheir findings.Soil health and plant health Soil can be acidic or alkaline – acidic soil is sometimes called ‘sour’ andalkaline soil is sometimes called ‘sweet’ soil.Most plants are very sensitive to acidity and will die if exposed to very acidicor very alkaline soil.We make soil more acidic when we add compost, manure and other organicmaterial.We make it more alkaline when we add lime (ground limestone or dolomitelime).The pH scale Look at students’ lists of examples of acidic foods. If someone says lemonjuice is ‘very acidic’ and someone else says orange juice is ‘very acidic’, doesthat mean they are exactly the same? (No.)Ask: Okay then, how do we communicate what the acidity is?An international agreement is called a standard, or a scale, and it helps usto talk about a measure like acidity in confidence that we are talking aboutexactly the same measure.Introduce the pH scale and discuss students’ experiences of some of thesubstances on the list.Explain that we are going to test some of the things in our kitchen but alsothe soil in our garden.Some plants prefer to grow in more acidic soil than others (blueberries,potatoes, radishes, carrots, beans and peanuts are some of the plants thatlove slightly acidic soil between 6 and 5.5 on the scale). Many Australianindigenous plants prefer slightly acidic soil, as much of the soil here isnaturally acidic. Most of our vegetables prefer soil that is very slightly on theacid side of neutral (pH 6 to 7 – remember 7 is neutral). (An obvious point tomake here is that these vegetables come from other countries, where the soilis slightly different.)Ask: Why would we need to know the acidity of the soil in our garden beds?}}To ensure that we plant the kinds of plants that will grow best andproduce beautiful fruit and vegetables for our garden.}}To see if we need to add anything to the soil to help the plants that arealready there. Stephanie Alexander Kitchen Garden Foundation 2011 (except where otherwise indicated).You may copy and communicate this material for non-commercial and educational purposes provided you retain all acknowledgements provided with the material.