Volcanic ash, a substrate suitable for plants

06/01/2015

"Nothing is lost, everything is transformed," reads the famous phrase of the French chemist Antoine de Lavoissier converted into a universal law. Under this concept, technicians from INTA Castelar's Institute of Floriculture analyzed the chemical and physical properties of volcanic ash -expelled by the Puyehue-Cordón Caulle volcanic complex in 2011- as a substrate for the production of potted plants.

According to Lorena Barbaro, a technician from the INTA Castelar Institute of Floriculture, "volcanic ash is a material with favorable chemical and physical properties and suitable for use as a substrate in the production of potted plants"Although he warned that his percentage must be defined in the formulation of the substrate according to the cultivation system.

Due to the enormous volume of ash available in the area, it is an ecological and low cost alternative that, in turn, would allow to decrease the tephra or volcanic material accumulated in the region.

In this sense, the researcher pondered the alternative because it is a material with low electrical conductivity and concentration of calcium, magnesium, potassium and sodium which allows to manage the mineral nutrient concentrations according to the requirements of the crop through fertilization.

In terms of physical properties, volcanic ash with a larger particle size is less dense and with greater porosity of aeration, while smaller ones have inverse properties. These properties are due to how these ashes were originated.

For this reason, Barbaro recommended supplementing substrates that are formulated with volcanic ash with other materials that improve the pore ratio with air and water or if used in pure form should be made a mixture of different particle sizes.

Among the most suitable for the production of coral plants, those formulated with 20% of fine ash and 50% of ash mixed were highlighted. Likewise, substrates formulated with 20 or 50% volcanic ash (fine, coarse or a mixture of both) and Sphagnum peat were able to obtain coral plants of the same quality as those developed in a commercial substrate.

In order to select the most appropriate formulation, a good particle size distribution must be taken into account to maintain an easily available water retention capacity and adequate air supply, low bulk density, high porosity, stable structure, low salinity, slightly acid pH and minimal decomposition speed.

What the eruption left

In June of 2011, the eruption of the volcanic complex Puyehue - Cordón Caulle expelled into the atmosphere large amounts of pyroclastic materials that covered almost 6 thousand hectares of the soil of Río Negro and Neuquén, whose 45% had a thickness of between 0,2 and 1,5 centimeters and the 55% with a thickness greater than 1,5 cm.

These materials receive different names according to their size and degree of consolidation. They are "blocks" when they are greater than the 32 millimeters (mm), "lapillo" when they measure between 2 and 32 mm, "trizas" between the 0,063 and 2 mm, and "pulvícula" the less than the 0,063 mm. The unconsolidated deposit is called "tephra" while the consolidated pyroclastic rock is known as "piroclastite".

In the vicinity of the volcano Puyehue - Cordón Caulle tephras were formed with lapillo or coarse ash and, in the most remote areas, trephors with pulvicles or fine ash with a chemical composition similar to other volcanic events of the same complex were formed.

Source: intainforma.inta.gov.ar