Particle Size of Dolomite Effect in Cinder-Based Media
Journal of Hawaiian and Pacific Agriculture 1993, Volume 4, Number 1
Download the full article, J Haw 10 002.pdf (PDF)
Introduction:
In Hawaiʻi, artificial media used in foliage production contains a small amount of peat moss in relation to black cinder. The starting media is often mildly acidic and not requiring much lime. However, the use of acid-forming fertilizers and heavy rainfall or irrigation may decrease the pH of the potting medium over time. It is not uncommon to find media pH levels of 4 or lower on the windward side of the island of Hawaiʻi where average annual rainfall exceeds 120 in (300 cm) and is slightly acidic. The majority of Hawaiʻi’s foliage production is located within this area and disorders attributed to low pH and related plant nutrient imbalances occur.
Selection of liming materials in terms of particle size for plant production under these conditions is a question that has often been raised by area nurserymen. Frequently used liming products in Hawaiʻi include dolomitic limestone and Kawaihae crushed coral, a calcitic limestone. The particle sizes for three dolomitic products and crushed coral are shown in Table 1.
The neutralizing value of a liming material depends on two factors: the purity of the limestone and the fineness to which it has been ground. The purity of limestone is expressed as the calcium carbonate equivalent where pure calcium carbonate is considered to have a neutralizing value of 100% and pure dolomitic limestone about 109%. Most agricultural limestones have neutralizing values of 90-98%.
The fineness of limestone determines its rate of reaction in the soil. The smaller the particle size, the greater the surface area exposed to soil particles and the greater its reactivity. Fineness is measured in mesh sizes which indicate the number of openings per linear inch in the screens (Table 2). Thus, the higher the mesh number the finer the particle size. Finer particles react more quickly than coarser particles, but the coarser particles may react over a longer period of time (Kelling and Schulte, 1980).
Most agricultural liming materials contain combinations of particle sizes. Selecting a liming material according to particle size depends on the grower's needs. When an immediate change in pH is desired, fine limestone with high proportions of 100 mesh size and smaller particles is desired. For greenhouse purposes, a fine limestone which reacts within 2 weeks is generally recommended. If the intent is not to greatly raise the current ph, a coarser material is sufficient. Ag a general purpose limestone for soils, a limestone having 50% passing through 100 mesh, 60% through 60 mesh, and 95% through 20 mesh allows half of the material to react immediately and the other half over a 2-3 week period (Hinnish, 1979). About 100% of limestone passing a 60 mesh screen is gone in 1 year while 50% of the 30-50 mesh and 80% of the 8-20 mesh fractions remain in the soil after 1 year and continue to react in subsequent years (National Crushed Stone Association, 1981).
The objective of this experiment was to determine the reactivity of commercially available liming materials with different degrees of fineness in a potting medium of 2:1 black cinder:peat moss (by volume).