Soil improvement at sand dune by using tropical peat.

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In order to evaluate the possibility of crop growth after improvement of the soil layer at sand dune in tropical coastal area, the effect of mixing of tropical peat and/or mountain soil into sand was examined. The following results showed the possibility of crop cultivation after improvement of the soil.1. Mixing of the peat and the mountain soil decreased hydraulic conductivity and increased water holding capacity of the sand ; too much mixing may cause poor drainage, aeration, and available water content. The optimum mixing ratio in dry weight basis was estimated to be 84 : 6 : 10 for sand peat mountain soil ; the mixing ratio increased the available water content 3 times.2. SPAC model simulation was applied to evaluate the effect of the mixing. Meteorological data and crop data were collected at sand dune area in Narathiwat province, the southmost of Thailand. The results showed that the optimum mixture condition increased transpiration 1.5 times more than original sand and drainage of infiltrated rainfall decreased from 43% to 27%.3. Eluviat ion of nutrition from soil layer was estimated by using the break-through curve and simulated drainage. All fertilizer in sand soil layer was estimated to eluviate by only 30% of yearly total drainage water ; 20% of fertilizer was estimated to remain after yearly total drainage water had passed.