JWSS - Journal of Water and Soil Science

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Successive cropping of potassium-demanding crops like sunflower leads to depletion of soil potassium (K). This study was conducted to investigate the different forms of K and quantity–intensity (Q/I) relationship for sunflower growing soils in Khoy region, West Azarbaijan province. Twenty composite soil samples were collected from different soil series. Different forms of K, including solution K (Kso), exchangeable K (Kex) and non-exchangeable K (Knex) were determined. The results showed that Kso values varied from 0.061 to 0.54 (mmol L-1), with an average of 0.28 (mmol L-1), Kav values ranged from 55 to 699 (mg kg-1), 265 mg Kg-1 on average, and Kex values ranged from 54 to 694 (mg Kg-1) with an average of 261 (mg kg-1). Furthermore, Knex values varied from 160 to 612 (mg kg-1), 261 (mg kg-1) on average. Available K (NH4OAc- extraction) was less than 250 mg Kg-1 in half of the soils indicating the depletion of potassium from these soils. The Q/I curves were predominantly located in the adsorption regions. The Q/I curves were linear and lacked the curvature part relating to loss and gain of potassium present in the specific sites. The PBCK values varied from 11 to 108 (cmolc kg-1)/ (mol L-1) 0.5 and an average of 38 (cmolc kg-1)/(mol L-1)0.5. There was a linear significant relationship between PBCK and CEC (r2=0.82***). The AReK values ranged from 0.0014 to 0.027 (mol L-1) 0.5 and 0.0076 (mol L-1)0.5 on average. There was a significant relationship between the values of AReK and those of the soil solution K (r=0.68**). The Ko values varied from 0.0050 to 0.49 cmolc kg-1and an average of 0.21cmolc kg-1. Additionally, there was a high significant relationship between the values of Ko and ARoK (r= 0.95***) in the soils under study.

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Organic acids play an important role in improving the bioavailability of soil nutrients. The objectives of this study were to determine the effect of oxalic acid on the release of soluble, exchangeable and non-exchangeable forms of K from micaceous minerals and potassium feldspars, and also to investigate the trend of K release by time. A laboratory study was carried out using a completely randomized design with two replicates. Biotite, phlogopite, muscovite, Zanjan and Yazd K-feldspars (< 50 &mu;m size) were treated with 0, 10 and 100 mM of oxalic acid solutions for a period of 5 hours and 20, 60 and 90 days. The amount of K was determined by flame photometer. The results indicated that most amount of soluble, exchangeable and no-exchangeable K was released by 100 mM of oxalic acid. The maximum soluble K (0.86 gKg-1) was released from phlogopite, and the maximum exchangeable and non-exchangeable K (1.5 and 29.6 gKg-1, respectively) were released from biotite. Muscovite with 0.19, 0.34 and 1.41 gKg-1 of soluble, exchangeable and non-exchangeable K, respectively, had the lowest release of K among the studied minerals. The kinetics K release from minerals consisted of two phases. The first phase was relatively rapid and then it had a slow rate until the end of the experiment. Given that the applied concentration of organic acid was high, potassium release during the experiment period did not reach the steady state. Therefore, a longer period of release experiment is suggested.