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Welcome to The Turf Zone podcast. This episode covers basalt as an alternative topdressing sand and carbon sequestration strategy on turfgrass systems. Written by David Toscano and Qiyu Zhou.

Mineral sands are essential to the construction and maintenance of golf courses, where they are used in putting green construction, bunkers, and topdressing. Topdressing sand is especially important to modern golf course agronomy because it helps create firm, fast putting surfaces. This sand is typically quartz-based and is extracted from terrestrial, fluvial, or coastal deposits. Because these deposits are finite, quartz sand is becoming increasingly scarce, particularly the medium to medium-coarse particle sizes that golf courses require.

ands derived from calcium- and magnesium-rich silicate minerals, such as basalt and dunite, are a potential alternative. Basalt is a dark-colored igneous rock formed by the rapid cooling of lava at or near the Earth’s surface. It is among the most abundant rock types on Earth and is already used in construction, road bases, and railroad ballast because of its strength and durability. Finer fractions of crushed basalt (<5 mm) are typically an industrial waste product left over from crushing boulders for roads and buildings, and basalt can also arise as a byproduct of quarrying other materials, such as limestone, granite, or metal ores. Because most basalt sand is an industrial byproduct rather than a purpose-mined material, its use generally carries a lower carbon footprint than mining virgin quartz sand for golf course use. A field experiment evaluates whether coarse basalt sand can substitute for quartz-based topdressing sand of a similar particle size distribution without compromising turfgrass functional and visual quality. The trial is conducted on sand-based putting greens under two application rates, on both creeping bentgrass and bermudagrass, with turfgrass quality, ball roll distance, firmness, and total organic matter monitored throughout. Basalt sand is darker than quartz sand, which may help warm putting surfaces in spring and support earlier green-up. In warmer climates and during summer drought periods, however, the darker color may exacerbate heat stress, particularly on cool-season grasses. Both heat stress and spring green-up are being monitored on the two grass species. Crushed basalt at a much finer size (<100 µm) is the material relevant to Enhanced Rock Weathering (ERW), a promising strategy for removing CO₂ from the atmosphere that has been investigated across a range of agricultural systems because it can potentially pair carbon dioxide removal with co-benefits to soil and crop productivity. The approach works by accelerating the natural weathering of silicate rocks through the application of finely ground rock to soil. The principle behind ERW is relatively simple. When water interacts with CO₂ from the atmosphere in the soil, it forms carbonic acid (H₂CO₃). This weak acid reacts with silicate minerals in basalt, causing the rock to dissolve and release elements such as calcium (Ca²⁺) and magnesium (Mg²⁺), as well as bicarbonate (HCO₃⁻). Natural rock weathering is a slow geological process that can take thousands of years. ERW accelerates this process by increasing the surface area and reactivity of silicate minerals. One of the major challenges is accurately monitoring and verifying of the weathering process associated with carbon removal. A comprehensive mass-balance approach requires tracing changes in Ca and Mg across soil, plant tissue, and leachate to estimate carbon sequestration which is a difficult undertaking under field conditions. The TiCAT method, which uses titanium as an immobile tracer to estimate silicate rock weathering, was developed to address this challenge but had never been evaluated on turfgrass sites. To compare these two approaches, the initial experiment evaluating both fine and coarse basalt were conducted in mesocosms under greenhouse conditions. These experiments provide early evidence on whether the TiCAT method can be effectively applied to estimate carbon sequestration in turfgrass systems. Beyond its carbon sequestration potential, existing research in row-crop agriculture suggests that fine basalt application can offer additional co-benefits: raising soil pH in a manner similar to lime, improving plant and soil health, and increasing nutrient use efficiency. To test whether these co-benefits extend to turfgrass systems, a field experiment is being conducted on bermudagrass grown on native soil, representing management regimes typical of golf course fairways and roughs, sod farms, and home lawns. Turfgrass visual quality and soil physical characteristics are being monitored to determine whether these co-benefits hold for turfgrass stands. You have been listening to The Turf Zone Podcast. Follow The Turf Zone on X, Facebook and LinkedIn for all things turfgrass, featuring podcasts, magazines, events and more.