KINETICS OF NATIVE POTASSIUM RELEASE AND POTASSIUM SUPPLYING CHARACTERISTICS TN SELECTED SOILS

Kinetics of native potassium release and potassium (K) supplying characteristics of 19 soils selected from 16 different soil types were investigated by using a continuous flow apparatus and pot experiments.The soils differed greatly in native K release process. The K releasing time ranged from 100 to 600 minutes. The ranges of maximum and average releasing rates were 0.46-20.55 mg kg-1 min-1, and 0.009-1.25 mg kg-1min-1, respectively. The total amount of K released ranged from 40 mg/kg to 430 mg/kg. The K release process in the soils can be described by first order equations with rate constant ranging from 5.48 10-1min-1 to 65.62 10-1min-1. Potassium release from most of the soils tested can be well described by a single first order equation. However, K release from soils dominated in mica and with some chlorite existing in the clay fraction showed two distinguished first order reactions with different rates. These may be attributed to different release mechanisms of K at different adsorption sites.Corn seedlings were grown for 5-7 harvests in pot expeifiinents to evaluate K supplying capacity of the soils. Results indicated that the kinstics parameters obtained from the kinetics study in the laboratory can be used to well characterize the K supplying capacity of the soils. Soils with higher total K release, higher releasing rate and longer releasing time, such as a chestnut soil from Qinghai, showed stronger K supplying power in pot experiments, while' those with lower total K release, slower releasing rate and shorter releasing time, such as a latosol soil from Guangdong, supplied a small amount of K to plants. A purple soil from Sichuan released a significant amouat of K ia the laboratory study, but it was released at a relatively fast rate in a relatively short time. Results from pot experiments indicated that this particular soil had a notable K supplying intensity initially. But the soil K reserve was depleted quickly with absorption by plants. The amouat of total K released from the soils in K release study was significantly correlated with the total K uptake by plants in pot experiments (r= 0.9056) .