Evaluation of Potassium status in Paddy soils of Gilan province

Getting more knowledge about Potassium status in paddy soils, can be benefitial for improvement of Potassium fertilizing management. One hundred and nine soil surface samples collected with uniform geographic distributions and pH variables, organic carbon, cation exchange capacity (CEC), particle size distribution, potassium extracted by normal ammonium acetate at pH7 (K-NH4OAC), Potassium extracted by boiling Nitric acid (K-HNO3)and water soluble potassium were measured. Clay and CEC have normal population without distinct subpopulation and with uniform variance. This condition could be arised from relatively uniform parent materials and similiarity of climatic condition and chemical process that affects these variables. Population frequency distributions of silt, O.C, water soluble potassium and pH were not normally distributed, with significant skewe and kutosis. Sand, K-NH4OAC, K-Nitricacid have log-normal distribution. Non-normallity in frequent distribution explains variation in diposital envoirnment sand non-symetric effects of pedogenic or hydrological processes. Regression coeffcents for potassium extracted by different methods for soil physio-chemical properties were weak but they were strong among K-NH4OAC, KHNO3 and water soluble potassium variables especially in the East of Gilan that indicated the existance of clay minerological uniformity in this region. Water-soluble potassium is affected by sand, O.C, K-NH4OAC and pH (R2a= 0.73). Available potassium is affected by water soluble potassium and cation exchangable capacity(R2a= 0.77). Potassium extracted by boiling Nitric acid affected by exchangable potassium silt(R2a= 0.55). Both available potassium and clay followed by spherical semivariogram model and with respect to mean correlation distance, maximum uniformity for available potassium obtained in 7862 meters. Geographic Distribution mapping of K-NH4OAC shows that center of Gilan, Particularly i n Sepeed-Rood watershed contains more available potassium than other regoins. This attributed to soluble potassium concentration in the river and sediments which are carried and added to paddy soils. There is less clay, CEC, K-NH4OAC and K-HNO3 contents in Fomanat region than other regions.Soils of this region are formed in ancient wede deposit and river alluvial deposit with high sand and low clay content. Therefore they have are less available and non-exchangable potassium. According to Quemener proposal index (33) and study of the potassium status, 68.8 percent of Gilan province paddy soils are from moderate to very low at soluble Potassium scale.