Aggregation Status on Soil Potassium in Illitic Loess Slowly Swelling Soils Possessing High Specific Surface Area

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From different zones of Golestan province, 61 soil samples from 0-30 centimeter depth with a wide range of physicochemical properties, were obtained. In figure 1, the sample sites are shown with different symbols each of which will be explained below. The violet thin film shown in figure 1 is the pathway of sample site. Vegetation cover type of Tuskestan, Shah-koh Shah-roud regions were varied including jungle, arable land and pasture. This district was named as Site A. The B site comprised Ramian and shosh-ab possessing jungle vegetation cover. And site C belonged to the main road way from Gorgan state toward Maraveh-tape, Dashli-boroun, Inche- boroun and final point Agh-ghala. This site is full of arable lands and as a consequence of the massive production of this zone, it is carrying the main responsibility of cultivation and agriculture industry of Golestan province on its shoulders.
2 types of Soil samples were taken from each site, one series get air-dried, gently crushed and passed through a 2-mm sieve for evaluating soil characteristics. The second one remained undisturbed for aggregation stability experiment.
Soil texture was evaluated via hydrometer methods (Page et al., 1986). Organic matter (OM) was determined (Walkey and Black, 1934). Cation exchange capacity (CEC) at pH 8.2 was measured (Chapman, 1965). Aggregate stability including mean weight diameter (MWD), geometric mean diameter (GMD), status and degree of aggregation (SOA&DOA), dispersion ratio (DR), was
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