Thailand is an agriculture-based country which produces large amounts of agricultural waste. Making biochar from this waste can reduce pollution, decrease costs of production, and increase C sequestration. The agronomic benefits of biochar are partly derived from the available plant nutrients in biochar. This study investigated the fertilizer value of biochars manufactured by slow pyrolysis. Pyrolysis temperature and feedstock type affect nutrient concentrations and nutrient element speciation in biochar. The physio-chemical, mineralogical and structural properties of biochars made from 14 agriculture wastes (soybean cake, corncob, lemon peel, sugar palm fibre, durian shell, tamarind wood, coconut fibre, coconut shell, bamboo wood, rice husk, eucalyptus wood, oil palm fruit, coffee waste, and bagasse) were investigated. The plant nutrients in biochar mostly occurred in crystalline minerals which were present on the surface and inside the cell structure of biochar. Most biochars examined in this research contained calcite (CaCO 3 ). The presence in biochars of several K-minerals [archerite (KH 2 PO 4 ), chlorocalcite (KCaCl 3 ), kalicinite (KHCO 3 ), pyrocoproite (K 2 MgP 2 O 7 ), struvite-K (KMgPO 4 × 6 H 2 O), and sylvite (KCl)] encourages the use of biochar as a K-fertilizer. Fibre, fruit and wood biochars contained considerable amounts of K, Ca, and P. Sugar palm and coconut fibres also contained high level of Na in halite. This study recommends the utilization of biochars manufactured from sugar palm fibre, coconut fibre, durian shell, and oil palm fruit as fertilizers. With their appreciable contents of plant nutrients in highly to moderately soluble compounds these biochars should be effective fertilizers, especially for use by organic farmers who cannot use any chemical fertilizers.

Rubber tree (Hevea brasiliensis) is of major economic importance in Southeast Asia and for small land holders in Thailand in particular. Due to the high value of latex, plantations are expanding into unsuitable areas, such as the northeast province of Thailand where soil fertility is very low and therefore appropriate management practices are of primary importance. Arbuscular mycorrhizal fungi (AMF) contribute to plant growth through a range of mechanisms and could play a key role in a more sustainable management of the rubber plantations. We described the diversity of AMF associated with rubber tree roots in Northeast Thailand in relation to tree age and soil parameters along a chronosequence of rubber tree plantations. Cassava fields were included for comparison. Rubber tree and cassava roots harbored high diversity of AMF (111 Virtual Taxa, VT), including 20 novel VT. AMF VT richness per sample was consistently high (per site mean 16 to 21 VT per sample) along the chronosequence and was not related to soil properties. The composition of AMF communities differed between cassava and rubber tree plantations and was influenced by soil texture and nutrient content (sand, K, P, Ca). AMF community composition gradually shifted with the age of the trees. Our results suggest that the high diversity of AMF in this region is potentially significant for maintaining high functionality of AMF communities.

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Twenty nine Fe oxide concentrates of Thai soils formed on basalt, sandstone, shale/limestone and granite were investigated. Goethite and hematite are relatively more abundant in granitic and basaltic soils, respectively. Values of Feo/Fed range from 0.01 to 0.28 indicating that free Fe oxides are mostly crystalline.There are no systematic differences in unit-cell dimensions for goethite and hematite in soils on different parent materials. Mean crystallite dimensions calculated from the 110 reflections are greater for hematite than for goethite. Aluminium substitution varies from 8 to 24 mole% for goethite and from 4 to 17 mole% for hematite. The dehydroxylation temperature for goethite ranges from 285ºC to 320ºC. The goethite in basaltic soils has a smaller crystal size and Al substitution, as well as a lower dehydroxylation temperature, compared to soils on other parent materials. The dehydroxylation temperature of goethite is positively related to Al substitution (R = +0.58), MCD110 (R = +0.49) and Ald (R = +0.53). The Mn, Ni, Cr, V and P in these soils occur in Fe oxides rather than as discrete minerals.

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Purified kaolins from Thai soil on diverse parent materials were characterized using analytical transmission electon microscopy, X-ray diffraction, thermogravimetric analysis and chemical analysis. The properties of Thai soil kaolins appear to be more diverse than Indonesian and Western Australian soil kaolins investigated using the same analytical procedures; this difference may reflect the greater range of parent materials for the Thai soils. The kaolins show a variety of crystal morphologies including euhedral hexagonal to subhedral platy crystals, tubes and laths and several morphologies were present in most samples. TEM-EDS enabled analysis of single crystals of each morphology present within a sample. Tubular or lath-shaped crystals usually have lower %Fe2O3 contents than hexagonal platy crystals in the same sample. The relationships between crystal size and Fe content within morphological populations were also examined by TEM-EDS. Generally, smaller kaolin crystals display a wider range of Fe concentration than the larger kaolin crystals in the same sample. Increasing Fe concentration in bulk samples is closely correlated to decreasing coherently scattering domain size (R2= 0.57), increasing cation exchange capacity (R2= 0.44) and increasing specific surface area (R2= 0.65). However the properties of the deferrated soil kaolins, including their Fe content, are not related to forms of Fe, (total Fe, amorphous or organic) in the untreated clay fraction of the soil.Inhibited vermiculite is a common minor constituent of these clay fractions and its average structural formula derived from EDS data indicates that it was formed by Al replacing K in muscovite. One Al3+ion occupies the interlayer space previously occupied by three K+ions. As the distances between these Al3+cations in the interlayer space is large it is proposed that isolated or loosely associated hydrated Al3+groups such as Al(OH2)63+exist that resist exchange by other cations due to hydrogen bonding with the adjacent tetrahedral oxygen surfaces

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The objective of this study was to determine if dithionite- and oxalate-extractable Fe and Al can be used to predict the P sorption capacity of Thai soils. Forty-five samples from diverse soil types were taken from surface and subsurface horizons of soils on sandstone, shale/limestone, granite, and basalt. The samples were analysed for P sorption, dithionite- and oxalate-extractable Fe and Al (Fed, Feo, Ald, Alo), specific surface area (SSA), and other soil properties. Generally P sorption data for these soils were slightly better fitted by the Langmuir equation than the Freundlich equation. The Langmuir P sorption maximum ranged from 35 to 1111 μg/g with a median value of 370 μg/g soil. Soils developed on basalt had higher values of P sorption maximum (xm) (range 400–1111 μg/g, median 597 μg/g) than soils on other parent materials. Fed concentrations in soils (4–74 g/kg) were much higher than Feo concentrations (0.2–13.8 g/kg) with values of Feo/Fed ranging from 0.01 to 0.28 (median 0.09), indicating that most of the free iron oxides were crystalline. Amounts of Ald and Alo were about equal with median values of 1.6 and 1.0 g/kg, respectively. About 80% of the samples had SSA values <40 m2/g. Both the P sorption maximum and Freundlich k were linearly related to SSA (R2 = 0.77, 0.74), Ald (R2 = 0.78, 0.79), Alo (R2 = 0.64, 0.74), Fed (R2 = 0.48, 0.41), Feo (R2 = 0.43, 0.72), and clay content (R2 = 0.48, 0.36). Stepwise regression indicated that 81% of the variability in P sorption by these soils could be explained by a combination of dithionite and oxalate Fe and Al, however, Ald alone is almost as effective in predicting the P sorption capacity of Thai soils.