A BLEND OF COMPOST AND PUMICE makes sense on several levels—pumice provides a buffer to the extreme volatilization taking place in the decomposing matter, mitigates nitrogen loss, and provides inert bulk that improves airflow. Then, once in the soil, pumice provides long-term soil performance improvement on a structural level.
Pumice Improves the Composting Process
The following studies show the viability of pumice as an amendment to the composting matter to improve the overall process and better meet the challenges presented by various feedstocks.
REDUCTION OF VOCs: A study published in Biosource Technology1 detailed research using natural material amendments blended at a 1:10 volumetric ratio with poultry litter to reduce VOCs during composting. The results quantified the effectiveness of pumice (at 100 days) to significantly reduce VOCs at an 88% reduction (with pumice out-performing the other materials tested).
MITIGATING NITROGEN LOSS: A study2 done by the Department of Environmental Engineering, Ondokuz Mayis University in Samsun, Turkey looked at improving nitrogen availability in composted poultry litter (mitigating NH3 volatilization) using natural amendments. It was found that natural materials significantly reduced NH3 volatilization. In particular, only 26% of initial total N was lost from the compost containing pumice.
EFFECTIVE BULKING AGENT: Bulking agents can reduce the cost, labor, time duration, and increase the compost quality and nutritive values. The choice of bulking agent is greatly dependant on what is being composted. For wet materials, a low-moisture, highly absorbent amendment like pumice meets the need.
A Chinese study3 quantified the contributions of pumice in sewage sludge composting when used as an inert bulking agent. Pumice, with its rich pore structure and strong water absorbent capacity, was found to significantly improve the biological reactions in the composting process in terms of material porosity, water-holding capacity, nitrogen absorption (promoting ammonia assimilation to organic nitrogen rather than loss to volatilization), and accelerating the composting period.
As an inert amendment agent to compost, pumice has none of the drawbacks of using organic bulking agents like straw, husks, wood chips or sawdust—pumice does not degrade and compact during the composting process, performs consistently, blends readily, and is easily sourced and stored. The physical nature of pumice also provides an ideal carrier for adding additional elements to the bio-formulation, such as sucrose3 (to add a carbon source and provide a growth platform to quickly ignite microbial action).
Pumice Provides Non-Consumptive Soil Conditioning
Compost is valuable for both the nutrients that it adds to poor or depleted soils and for the physical improvement it makes to the soil structure itself. A properly-structured root zone is vital to sustained growth, and composted organic matter provides structural benefits...until the organic matter is exhausted.
Reconditioning the soil every few years with a fresh load of compost is doable in a garden or flowerbeds, but for landscaping and reclamation projects, a more permanent solution to poorly structured soils is needed. That’s where pumice-blended compost comes in.
The foamed-glass character of pumice provides the key physical soil-improvement benefits needed by structure-poor soils—it lightens soil texture, resists compaction, improves drainage and aeration, moderates soil temperature, enhances pore space, retains moisture—and does so indefinitely, as it will not break down nor leach out over time.
PUMICE-AMENDED SOIL PERFORMS: A study4 published in the Journal of Central European Agriculture (2005) measured strawberry seedling growth in pumice-amended soil and determined “important level” increase in growth, attributed to the studied enhanced moisture retention and pore size distribution factors contributed by the pumice amendment.
Another study5 concluded “that pumice may be effectively used in specific amounts for improving aeration and bulk density conditions of poorly structured soils.”
The Australian Journal of Crop Science published a study6 that looked at adding pumice to achieve gains in soil moisture absorption and retention for maize (corn) crops. The results showed that “pumice significantly increased the amount of soil moisture retention compared to control. Growth characteristics of maize (vegetative growth and yield) were significantly improved with increasing amount of pumice concentration.”
STUDIES REFERENCED ABOVE:
 Removal of Volatile Organic Compounds by Natural Materials During Composting of Poultry Litter. (Bioresource Technology, 2008) Department of Environmental Engineering, Ondokuz Mayıs University, Samsun, Turkey; by N.G. Turan, A. Akdemir, O.N. Ergun.
 Nitrogen Availability in Composted Poultry Litter Using Natural Amendments. Department of Environmental Engineering, Ondokuz Mayis University, Samsun, Turkey; by N. Gamze Turan. firstname.lastname@example.org Waste Manag Res. 2009 Feb
 Usage of Pumice as Bulking Agent in Sewage Sludge Composting. (Bioresource Technology, 2015) Harbin Institute of Technology, Harbin 150090 & School of Environment, Henan Normal University, Xinxiang 453007, China; by Chuandong Wu, Weiguang Li, Ke Wang, Yunbei Li.
 Effect of Pumice Amendment On Physical Soil Properties and Strawberry Plant Growth. Ustun SAHIN, Selda ORS, Sezai ERCISLI, Omer ANAPALI, Ahmet ESITKEN; Atatürk University, Department of Agricultural Structures and Irrigation, Erzurum-Turkey
 Addition of Pumice Affects Physical Properties of Soil Used for Container Grown Plants. Ustun SAHIN, Omer ANAPALI; Agriculturae Conspectus Scientificus (ACS) 01/2006; 71(2)
 Soil Water Retention and Maize (Zea mays L.) Growth as Effected by Different Amounts of Pumice. Ashraf Malekian, Einollah Valizadeh, Mona Dastoori, Sohaila Samadi, Vahid Bayat; Department of Agriculture, Payame Noor University, PO Box 19395-3697, Tehran, Iran
Liberally blend pumice Compost Amender with organic feedstock. A generous layer of pumice can also be put down each time new layers are added to the compost pile.
ADDITIONAL INFORMATION and SUPPORT DOCUMENTS:
» Knowledge Brief: Pumice in Compost Improves Both the Biological Process and In-Soil Performance. (PDF)
» InfoGraphic: Determining Soil Type (Jar Method; PDF)
» Knowledge Brief: Conditioning Soil with Pumice (PDF)
» Technical Data: the physical and chemical properties of our natural pumice.
» Pumice Safety Data Sheet (PDF)
|Compost Amender works on two levels: by improving the biological composting processes, and then providing in-soil structural improvements to poor native soils, functioning long after the organic compost elements are consumed.
» Size/Grade: One-Eighth Fines, MN (1/8-inch stones with extensive pumice fines)
|Technical Data Sheet (PDF) for Compost Amender|
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