The growth of teak (Tectona grandis L. f.) seedlings in sandy soil in northeast Thailand is suppressed by infertility and drought stress. In a preliminary field pot experiment, we confirmed that bentonite was useful for increasing soil water availability. To monitor early growth characteristics of teak seedlings in sandy soil, we curried out an experiment of teak seedlings using bentonite and fertilizer in the field from July 2014 to November 2015. We then compared the growth, biomass, photosynthetic rate, leaf water potential, and concentration of elements in the plant organs among the four treatments. Bentonite increased both soil pH and Ca during the experimental period, and retained P in fertilizer. The dry mass of teak seedlings was markedly increased by concurrent use of bentonite and fertilizer. However, the use of bentonite alone showed little increase of dry mass of teak seedlings. Moreover, application of bentonite was mitigated drought stress in dry season, and photosynthetic rate showed high value by high concentration of chlorophyll. The concentration of K in root of teak seedlings was increased by application of bentonite, and its value showed positive correlation with the relative growth rate of teak seedlings. We concluded that bentonite was useful for the uptake of K and retention of P in fertilizer, as a result, growth of teak seedlings was accelerated.

When teak (Tectona grandis L. f.) is planted on acrisols in Northeast Thailand, its growth is suppressed by low pH, infertility, and low water holding capacity. To examine materials capable of increasing water holding capacity in soil and improving teak growth, we conducted an experiment with teak seedlings. We selected bentonite, charcoal, and corncob and added these materials at a rate of 4% to sandy soil from northeast Thailand. Teak seedlings were potted on these soils and raised from July 2013 to July 2014. We compared growth, photosynthetic rates, leaf water potential, and concentrations of elements in plant organs among bentonite, charcoal, corncob, and no addition (control) treatments. Water content in the soils was increased for the bentonite and charcoal treatments. Teak seedlings potted in these two conditions did not suffer from drought stress. Comparing the growth traits of the teak seedlings, the charcoal treatment produced larger root growth and promoted the uptake of phosphorus and potassium, whereas the bentonite treatment did not show positive effects on growth or nutrient acquisition. In contrast, the corncob treatment decreased water content in the soil, and teak seedling growth was suppressed. We concluded that charcoal was a useful material to improve teak growth in sandy soils.

To verify the acclimation capacity of evergreen Fagaceae species on calcareous soil, we compared ecophysiological traits between Quercus glauca Thunb., Q. salicina Blume, Q. myrsinaefolia Blume, and Castanopsis cuspidata (Thunb.) Schottky as typical woody species from southwestern Japan. We also examined the inoculation effects of the ectomycorrhizal (ECM) fungi Astraeus hygrometricus and Scleroderma citrinum, and planted seedlings in calcareous soil collected from a limestone quarry. We measured growth, ectomycorrhizal colonization, photosynthetic rate, and concentrations of nutrients in plant organs for A. hygrometricus-inoculated, S. citrinum-inoculated, and non-ECM seedlings. Six months after planting on calcareous soil, seedlings of the three Quercus species inoculated with A. hygrometricus were larger than non-ECM seedlings, especially Q. salicina, which showed the greatest increase in dry mass. The dry mass of C. cuspidata seedlings was inferior to that of the three Quercus species. In the nutrient-uptake analysis, phosphorus, manganese, and iron uptakes were suppressed in calcareous soil for each Fagaceae species. However, seedlings of Fagaceae species that showed better growth had increased concentrations of phosphorus in roots. We concluded that seedlings of Q. salicina and Q. glauca inoculated with A. hygrometricus were best suited to calcareous soil and were considered as useful species for the reforestation in limestone quarries.