Abstract:In this paper, laboratory incubated experiments (25℃) were carried out to study the characteristics of release and distribution on different amount of rice straw potassium (K) and chemical potassium (K) in the water-soil system. Results showed that pH of surface water dealing with application of straw potassium 300 mg/kg through a process, namely from weak acidification to weak alkalization. Nevertheless,treatment with chemical potassium reduced pH of flooded solution. In steady situation, pH of surface solution had a positive correlation (R2 = 0.938**) with rice straw potassium, but a negative correlation with chemical potassium (R2 = 0.993**). For the treatment with 300 mg/kg chemical potassium, surface water soluble K was highest (50.64 mg/L) on day 0, and then tended to decrease. Unlike surface water soluble K, slowly available K reached the maximum value (414.51 mg/kg) on day 5, and then maintained dynamic stability. However, available K content continued to rise before day 25. For the treatment adding 300 mg/kg rice straw potassium, surface water soluble K first reached the maximum value (52.70 mg/L) on day 3 and then decreased gradually. For the same time, K concentration of surface water adding 300 mg/kg straw potassium was higher than that of chemical potassium treatment. Different potassium rates results indicated that when the amount of applied potassium was 150 mg/kg, two kinds of potassium mainly existed as exchangeable K, followed by soluble K. With the increment of extra potassium, fixation-K began to be increased. For the equivalent potassium rate, the proportion of exchangeable K was higher in the treatment with rice straw potassium than the treatment with chemical potassium whereas the proportion of non-exchangeable K of them were on the contrary. There were no significant differences on the fixation-K of soil between straw potassium and chemical potassium when the amount of added potassium was within the threshold. When the amount of extra potassium was beyond the threshold, adding straw to soil could reduce K fixation.