Crystalline Forms of Plant Nutrient Elements in Tropical Biochar.

Crystalline forms of plant nutrient elements in tropical biochar Nattaporn Prakongkep1, 2, Wanpen Wiriyakitnateekul3, Apinya Duangchan4 and Robert J. Gilkes1 1School of Earth and Environment, University of Western Australia, Crawley, 6009, Australia 2Department of Soil Science, Faculty of Agriculture, Kasetsart University, 50 Phaholyothin Road, Chatuchak, Bangkok, 10900, Thailand 3Office of Science for Land Development, Land Development Department, Phaholyothin Road, Chatuchak, Bangkok, 10900, Thailand 4Department of Chemical Engineering, Faculty of Engineering, Kasetsart University, 50 Phaholyothin Road, Chatuchak, Bangkok, 10900, Thailand Abstract We characterised 26 biochars, made from 16 biomass wastes (soybean cake, corncob, lemon peel, sugar palm fibre, durian shell, spanish plum fruit, tamarind wood, coconut fibre, coconut shell, rice husk, liquid fertilizer residue, bamboo wood, eucalyptus wood, oil palm fruit, coffee waste and bagasse). We evaluated biochars produced by three procedures including a traditional method. Biochar properties including morphology, mineralogy and chemical composition varied substantially between biomass types and plant organs but there were no systematic differences between three methods of biochar manufacture (Kasetsart University: 400-550oC and 200 cm3/min N2 flow rate; Land Development Department: 400oC with 300 cm3/min N2 flow rate and a traditional kiln). Generally, the morphology of biochar particles faithfully preserves the morphology of the parent plant organ despite radical chemical transformation. The composition of minerals was determined by chemical analysis, XRD and SEM-EDS of biochar and indicated that biochar may be a significant source of plant nutrients, especially potassium, calcium, phosphorous and sulfur. Some of the 32 minerals observed in biochar (e.g. aragonite (CaCO3), apatite (Ca3(PO4)3OH), butschlite (K2Ca(CO3)2), calcite (CaCO3), dawsonite (NaAl(CO3)(OH)2), monetite (CaHPO4)) have low water solubility, and so the release of nutrient elements will be retarded. Conversely, arcanite (K2SO4), kalicinite (KHCO3), sylvite (KCl) and epsomite (MgSO4.7H2O) are highly soluble. It is clearly important to understand biochar and soil properties, local environment conditions and plant nutrient requirements before evaluating whether biochar should be applied to a soil. The traditional practice of using biochar is to reduce the persistence of pathogens in organic residues and has the additional benefit of providing a nutrient supplement to infertile soils. Keywords biochar; tropical plants; crystalline forms; chemical composition