Soil amendments

Soil amendments are organic or inorganic materials that are added to the soil to improve its physical, chemical and biological properties. Soil amendments are generally used to overcome specific soil constraints, such as water infiltration, nutrient retention, or soil structure, or to target specific soil constraints, such as water infiltration, nutrient retention, or soil structure, or to target improved function in soil. Some common soil amendments (organic and inorganic) include animal manure, compost, worm castings, gypsum, lime, clay, straw, sawdust and wood chips.

Soil amendments can be easily applied on the surface, broadcast or mixed into the topsoil, or targeted for delivery and potentially mixed into the subsoil. These applications can target specific soil properties (e.g. water repellence) or simply boost nutrient availability (e.g. additional nitrogen) for soil organisms to consume.

For example Eco-Wet® is a soil wetter designed for fast water penetration with longevity which holds water in a range of soil types. For more information about Ecogrowth’s Eco-Wet® read our technical article covering Eco-Wet® Trial Data In Broadacre Applications.

Soil amendments have a range of considerations to ensure best practice soil management. The most important factor is determining soil biology and constraints, targeting solutions to address these.

Longevity

Soil amendments vary in quality and composition, and depending on the characteristics of the material, they can cause rapid or slow changes that are suited to different production or management aims. When seeking a soil amendment for rapid changes, one that decomposes or solubilises faster will often take effect more quickly. However, if aiming for long-lasting changes, slow-acting amendments may be better suited.

Salinity

Many soil amendments contain high salt content (e.g. biosolids), so when managing soil that is high in salt, amendments lower in salt should be selected.

Logistics

Beyond the properties that amendments can change in soil, practical factors may influence the management of soil amendments. These should be considered when choosing a soil amendment:

• Availability.
• Transportation.
• Application.
• Storage.
• Cost.

Soil Texture & Particle Size

Sandy soils have larger soil particles, meaning generally that sandy soil is poor at water retention (and often nutrient uptake as well). This makes soil amendments with high water retention a good option.

Clay soils have smaller soil particles, meaning that amendments that improve soil aggregation and porosity are a good choice. Clay soils also often have low permeability, so they are suited to soil amendments that increase permeability.

Alkaline soils (defined by clay texture and a soil pH > 7.) can range from sandy soils to heavy slay and fine silt. Due to high levels of sodium or  lime, soil structure collapses from dispersion, which causes reduced water infiltration and increased surface density. Alkaline soils are suited to amendments that incorporate organic matter to acidify the soil and lower the pH, thereby improving the soil structure.

Human Health

Organic certification standards require organic waste, such as animal manure, to be put through the composting process before use to decrease the number of harmful pathogens present. Additionally, biosolids such as aging manure used as soil amendments may contain significant amount of heavy metals and are unsuitable for application to soil.

Fertilisers and soil amendments are added to the soil to promote healthy plant growth. Liquid fertilisers and granular fertilisers are concentrated plant food delivered to increase nutrient supply, while soil amendments may change the soil pH, improve soil structure, or balance nutrient deficiencies.

Soil amendments should be applied regularly, as precipitation washes nutrients away, growing crops deplete nutrients, and soil compacts over time. The frequency of amendments depends on your and site conditions, as well as the type of crops or plants.