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AGGREGATES AND PORE SIZE DISTRIBUTION FOR SOIL AT DIFFERENT GYPSUM CONTENTS | ||
| The Iraqi Journal of Agricultural Science | ||
| Article 1, Volume 40, Issue 5, 2009, Pages 22-36 | ||
| Author | ||
| Abstract | ||
| The objectives of this experiment were to assess the structure of soil at different gypsum content (5-502 gm gypsum. Kg-1 soil), by studied the aggregate size distribution and mean weight diameter (MWD). Then after assess the pore system for this soil by studied air filled porosity, storage pores, available water holding capacity, the slope of water retention curve and the pore size distribution. The aggregates size distribution was measured by wet sieves. The soil-water retention curve was also estimated, and used a computer program to determine the best-fit for experimental data of water potential verses volumetric water content which have nonlinear relation and to determine the parameter of van Genuchten (28) equation α, n and m. The derivative of van Genuchten (28) equation was used to measure the change in the slope of soil water retention curve for estimate the capacity of soil water retain or lost at deferent water potential as function of pore size distribution. The capillary rise equation was used to estimate the effective pore diameter. The result show that gypsiferous soil has weak structure and the aggregate size distribution which type microaggregate, less than 250 μm in diameter was more than 80%. The MWD was decreased from 0.375 to 0.165 mm when gypsum content increase from 5 to 255 gm gypsum.kg-1 soil, and then the value of MWD increased to 0.252 mm for sample 502 gm gypsum.kg-1 soil. The slope of soil-water retention curve increased with increasing gypsum and the maximum peak of slope found at 50 kPa water potential for soil gypsum content 502 gm gypsum.kg-1 soil. The pore volume increased with decrease the effective diameter it is ranged between 64 and 90 cm3.cm-3 for pores in diameter less than 29.8 μm, these result associated with decrease gypsum content in soil. The air filled porosity ranged between 10 and 36 cm3.cm-3 for pores in diameter more than 29.8 μm. The air filled porosity increased with increasing gypsum content in soil. | ||
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