Vermicompost Effect on Potassium Release Rate from Some Vineyard Soils of Malayer Area with Different Textures

Vermicompost, as a nutrient-rich organic amendment, contains most nutrients in plant-available forms and can influence soil fertility and plant growth significantly. The objective of this study was to investigate the availability and release rate of potassium (K) in six vineyard topsoil (0-30 cm) with different textures (loam, clay loam, and sandy clay loam) treated with 2 % of cattle manure vermicompost (VC), through successive extractions with 0.01 mol L-1 CaCl2 over periods of 0.25-72 hours. The results showed that VC addition to soils increased the K availability. The average cumulative K released after 72 h from the control and treated soils was 526.9 and 547.9 mg kg−1, respectively. Due to the conformity of data to the Simple Elovich Equation it was suggested that process of K release from soils was affected by diffusion processes. Simple Elovich rate constant values in soils ranged from 34.9 to 132.1 mg kg−1h-1.The VC had different effects on K release rate in soils. In clay loam soils with high clay content, low organic matter and K fixation capacity, VC increased K release rate, while in loam and sandy clay loam soils with low clay, high organic matter, and low K fixation capacity, it decreased K release rate. Overall, VC had a balancing effect on K release rate. It could be related to VC interaction with soil particles, especially clays. Due to the importance of K in grape nutrition and K deficiency in some soils, the use of VC in vineyards is recommended.