Comparison of Soil Potassium Extracting Methods to Determine Suitable Extractants for Sepeedrood Rice Variety in some Guilan Rice Paddy Fields

High-yielding rice varieties are prevailing in Guilan Province which is one of the most important rice producing regions in Iran. However, little is known about K status in this region and no suitable extraction method can yet be introduced to the farmers. This experiment was carried out to determine the available K by 15 chemical extractants and also to examine the critical K levels in paddy soils of the region. The treatments included 23 soils and 2 K levels (0 and 300 mg/kg as KCl) in a factorial experiment in a randomized complete block design with three replications. Results indicated that K application increased grain and straw yields, K concentration in straw as well as K uptake by rice. High correlation coefficients were observed between MgOAc, H2</sub>SO4</sub>, Morgan and 0.01 M CaCl2</sub> methods with K concentration in straw (0, 0.83, 0.78, 0.8 and 0.78, respectively) and with K concentration in plant tops (0.79, 0.76, 0.75 and 0.73, respectively). Similarly, high correlation coefficients were observed between the same extraction methods with K absorbed by straw (0.83, 0.82, 0.78 and 0.76, respectively) and with total plant K uptake (0.79, 0.83, 0.74 and 0.71, respectively). Potassium critical levels by different extracting solutions were determined by Cate-Nelson procedure and were 38, 74, 160, 111, 36, 112 and 100 mg kg-1</sup> for MgOAc, Morgan and Kelowana methods, Texas method H2</sub>SO4</sub> 0.01 M CaCl2</sub> and NH4</sub>OAc without and with submergence of soil samples, respectively. In this study, available K was below the critical level in almost 75% of the soils.