Land plaster is a soil amendment used in agriculture and gardening to improve soil quality and optimize crop yields. Growers use it to address specific chemical imbalances and physical limitations, particularly in heavy or problematic soils. It provides benefits without altering the soil’s acidity level.
Defining Land Plaster
Land plaster is the common name for the mineral gypsum, or calcium sulfate dihydrate. This naturally occurring compound forms from the evaporation of saline water and is mined from geologic deposits. It is crushed and screened into a fine powder or granules for agricultural use.
Land plaster is also frequently sourced as a byproduct from industrial processes, such as scrubbing sulfur from power station exhaust gases. Regardless of its origin, agricultural land plaster consists primarily of calcium sulfate, which is moderately soluble in water. This solubility allows the beneficial components to dissolve and move into the soil profile more effectively than many other mineral amendments.
Primary Roles in Soil Health
Land plaster functions as a dual-nutrient fertilizer, supplying two secondary plant nutrients: calcium (Ca) and sulfur (S). Calcium is important for strengthening cell walls, regulating enzyme activity, and ensuring proper development of new tissue. Sulfur is a component of amino acids and proteins, necessary for chlorophyll formation and overall plant metabolism.
Land plaster is particularly valuable for improving the physical structure of clay-heavy soils through a process called flocculation. The calcium ions cause dispersed clay particles to bind together, forming larger aggregates. This aggregation enhances the soil’s porosity, which leads to better water infiltration, improved drainage, and increased aeration for deeper root growth.
Land plaster also helps mitigate two common soil chemistry problems: aluminum toxicity and sodicity. In highly acidic subsoils, soluble calcium moves deeper than lime to displace toxic aluminum ions, allowing plant roots to penetrate the subsoil. For sodic soils, which contain excess sodium, the calcium replaces the sodium ions on the soil’s exchange sites. This allows the harmful sodium to be leached out of the root zone by irrigation or rainfall.
Application Guidance for Land Plaster
The precise application rate for land plaster should always be determined by a recent soil test, as specific soil deficiencies dictate the required quantity. For general soil conditioning, application rates typically range from one to two pounds per 100 square feet for garden beds. Commercial agriculture rates can be much higher, sometimes requiring up to 1,000 pounds or more per acre.
Land plaster is most commonly applied using the following methods:
- Broadcasting with a fertilizer spreader, often before planting or during early growth stages.
- Lightly incorporating the broadcast material into the top few inches of topsoil to improve structure.
- Injecting as a solution directly into irrigation systems, which requires specialized equipment and a fine-grade product.
Application timing is flexible since land plaster works slowly over time and can be applied whenever the field is accessible. However, for certain crops, such as peanuts, timely application at the beginning of the blooming period is important. Since the powder form can be dusty, wear personal protective equipment, such as a dust mask and safety goggles, during handling and spreading.
Land Plaster Compared to Agricultural Lime
The difference between land plaster and agricultural lime is a key distinction for managing soil health. Agricultural lime, primarily calcium carbonate, is applied specifically to raise the soil’s pH level and neutralize acidity. This occurs because the carbonate component reacts with the acid in the soil.
Land plaster, conversely, is chemically neutral and does not significantly alter the soil’s pH when it dissolves. This characteristic makes it the preferred choice when a grower needs to supply calcium or sulfur, or improve soil structure, without changing the existing acidity. The choice depends entirely on whether the primary soil problem is acidity or a deficiency in calcium, sulfur, or soil aggregation.