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TECHNICAL REPORTS

Waste Management

Co-composting of Acid Waste Bentonites and their Effects on Soil Properties and Crop Biomass

^a International Water Management Institute (IWMI), Southeast Asia Regional Office, c/o WorldFish P.O Box 500 GPO, 10670 Penang, Malaysia. S. Suzuki, present address, National Agricultural Research Center for Hokkaido Region, Hitsujigaoka Toyohira-ku Sapporo 062-8555, Japan
^b Land Development Department (LDD), Chattuchak, Bangkok 10900, Thailand

^* Corresponding author (w.soda{at}cgiar.org)

Received for publication December 13, 2005. Acid waste bentonite is a byproduct from vegetable oil bleaching that is acidic (pH < 3.0) and hydrophobic. These materials are currently disposed of in landfills and could potentially have a negative impact on the effective function of microbes that are intolerant of acidic conditions. A study was undertaken using three different sources of acid waste bentonites, namely soybean oil bentonite (SB), palm oil bentonite (PB), and rice bran oil bentonite (RB). These materials were co-composted with rice husk, rice husk ash, and chicken litter to eliminate their acid reactivity and hydrophobic nature. The organic carbon (OC) content, pH, exchangeable cations, and cation exchange capacity (CEC) of the acid-activated bentonites increased significantly after the co-composting phase. In addition, the hydrophobic nature of these materials as measured using the water drop penetration time (WDPT) decreased from >10 800 s to 16 to 80 s after composting. Furthermore, these composted materials showed positive impacts on soil physical attributes including specific surface area, bulk density, and available water content for crop growth. Highly significant increases in maize biomass (Zea mays L.) production over two consecutive cropping cycles was observed in treatments receiving co-composted bentonite. The study clearly demonstrates the potential for converting an environmentally hazardous material into a high-quality soil conditioner using readily available agricultural byproducts. It is envisaged that the application of these composted acid waste bentonites to degraded soils will increase productivity and on-farm income, thus contributing toward food security and poverty alleviation.

Abbreviations: SB, soybean oil acid waste bentonite • PB, palm oil acid waste bentonite • RB, rice bran oil acid waste bentonite • RH, rice husk • RH_a, rice husk ash • CL, chicken litter • OC, organic carbon • CEC, cation exchange capacity • WDPT, water drop penetration time • pH_w, pH measured in water • pH_Ca, pH measured in calcium chloride