Soil Texture, Nutrients and Cultivation Although large particles of sand hold fewer nutrients, sand drains well and is simple to cultivate. While clay particles hold the most nutrients of the main soil types, it compacts or packs down easily, making it difficult to till.

Often referred to as topsoil or black dirt by landscape companies, loam is a mixture of sand, clay, and silt. The estimated mixture is 40% sand – 40% silt – 20% clay. Loam is just the right mixture of all three that it holds nutrients well, retains water but still drains properly and allows oxygen to infiltrate.

Soil is a major source of nutrients needed by plants for growth. The three main nutrients are nitrogen (N), phosphorus (P) and potassium (K). Together they make up the trio known as NPK. Other important nutrients are calcium, magnesium and sulfur.

Clay, because of its density, retains moisture well. It also tends to be more nutrient-rich than other soil types. The reason for this is that the particles that make up clay soil are negatively charged, which means they attract and hold positively charged particles, such as calcium, potassium, and magnesium.

Gypsum can also help improve soil structure. Adding gypsum to the soil reduces erosion by increasing the ability of soil to soak up water after precipitation, thus reducing runoff. Gypsum application also improves soil aeration and water percolation through the soil profile.

A single application of gypsum is sufficient for three years and can be applied at any time of the year.

Clay Soil

1. Add powdered gypsum at the rate of two to three handfuls per square metre, then dig the soil over and water it in.
2. However, for a quicker option, for example, in planting holes, use a liquid clay breaker with organic matter*.
3. Add a handful of powdered gypsum to the bottom of the planting hole.

Lime vs gypsum Lime is a carbonate, oxide or hydroxide of calcium. It is used to increase soil pH and provide calcium ions in the soil. Gypsum is calcium sulphate. It is also used to provide calcium ions in the soil, but does not have the effect of increasing soil pH.

Gypsum therefore improves soil conditions much more rapidly than lime and will affect soil conditions to a greater depth than lime will. Gypsum will supply calcium to deeper depths than lime. This will improve subsoil conditions, and allow for greater root growth (better nutrient and water efficiency).

Hazards of Using Gypsum If handled improperly, gypsum can cause irritation to the skin, eyes, mucous membranes and the upper respiratory system. Symptoms of irritation can include nosebleeds, rhinorrhea (discharge of thin mucous), coughing and sneezing. If ingested, gypsum can clog the gastrointestinal tract.

You shouldn’t add lime to potatoes or sweet potatoes, and nor should you use lime if you are trying to grow tomatoes or capsicums. Many types of berries prefer acidic soils, and blueberry bushes, raspberries and strawberries won’t do well if you apply lime. The same is also true of grapes.

Two materials commonly used for lowering the soil pH are aluminum sulfate and sulfur. These can be found at a garden supply center. Aluminum sulfate will change the soil pH instantly because the aluminum produces the acidity as soon as it dissolves in the soil.