It seems apparent to me that many people think that if a soil is black it is good. I presume it is because some of Australia’s most fertile soils are black. However around here it can be a trap for new players the compacted marine sand that has been removed from many ofthe developments around the coast is a prime example. It is a rich black colour sure enough but at closer inspection you will find it has a high salt content and is often quite acidic (pH 4.5-5.5)and is devoid of any structure and therefore will set like concrete. The result being it will slowly kill your plants as they battle to uptake the nutrients and are starved of the air needed to grow.
So what should you be looking for in a soil. Given that much of the soil in the hinterland has a very thin “Ahorizon” or Top Soil over very heavy clay. The ideal soil you should be looking for is a sandy loam. Without going into to much detail I think it is necessary at this point to define Loam.
Loamis a mixture of silt or sand and clay, loosely coherent (friable)with an admixture of organic matter or humus. Therefore in order to be classified as loam it is essential that it has all of the above. To assess the amount of sand, silt, clay and humus in a soil there is an easy experiment you and your kids can do at home.
Take a straight sided glass jar or measuring cylinder and add a handful of soil and then add water so there is approximately 50-50 soil-water. Then shake vigorously and leave to stand for a day. The layers separate into distinct bands with the coarse sand in the lowest layer then fine sands, silts, clays, and finally organic matter or humus on the top. The humus is particularly important because it binds soil particles together to form soil crumbs which provide air pockets, greatly increases the water holding capacity and the drainage of a soil, and packages soil nutrients in a way that is easily accessed by plants.
Soil Structure is probably the most important features of soil and this is where the term loosely coherent or friable comes in. What this really means is that it will hang together on compression, but contains many tiny spaces in which air is trapped so that it can be recrumbled with pressure between the fingers. It is particularly important that these air pockets are maintained even after soaking with water.