Abstract

Paddy soils are important in Guilan province because they are the base of agriculture. So, it is necessary to recognize and analyse paddy soils for understanding of their limitations and optimum using. Sefidrood plateaus and upper terraces, river alluvial plain, lowland and Caspian sea coastal plain physiographic units in a toposequence in Sangar Dam uplands in adjacent of Rasht city to Caspian sea shore were recognized. Five profiles were studied on each physiographic unit, which one of them was selected in order to detail study as reference profile. Physical and chemical characteristics of paddy soils formed on mentioned physiographic units were studied by providing disturbed soil samples from the horizons of described soils. Results showed that soil structure was weak granular in all surface horizons and single grain in the subsurface horizons of the Coastal plain. Soil structure was subangular blocky and angular blocky in the subsurface horizons of other units. Organic matter was high in surface horizons because of accumulation of rice residues. Organic mater was the highest level in lowland due to high ground water table and lower decomposition rate. Cation exchange capacity (CEC) was high in lowland and alluvial plain due to high organic matter and clay content in soils. Clay particles in plateaus lands were lower than other units because of alteration, suitable aeration and occurrence of ferrolysis. Electrical conductivity was high in subsurface horizons of lowlands and coastal plain because of high ground water table. Exchangeable Na+ was high in subsurface horizons of coastal plain and lowlands due to sea water seepage from depth in these soils. Soil reaction was nearly neutral because of natural and artificial submerged effect.

Key words: Chemical properties, Guilan, paddy soils, physical properties, puddling.